Introduction
In theory, diagnosing gestational diabetes mellitus (GDM) and implementing intensified treatment in affected women reduce the risk of foetal macrosomia, minimise serious peripartum complications and prevent postpartum health deterioration in the child. Dietary interventions play a key role in reducing the risk of developing GDM, with evidence suggesting that healthy eating patterns, such as adherence to a low-glycaemic index diet, increased fibre intake, reduced saturated fat consumption, Mediterranean or Dietary Approaches to Stop Hypertension (DASH) dietary guidelines and gestational weight gain (GWG) limitations, can contribute to improved glucose metabolism and lower GDM incidence(Reference Michalopoulou, Jebb and Astbury1). The risk of developing type 2 diabetes mellitus (T2DM) in women who are diagnosed with GDM is ten times greater than that in women without GDM(Reference Herath, Herath and Wickremasinghe2). A Danish study monitoring 151 participants over a median 19-year follow-up period revealed the following statistics: 29% were diagnosed with prediabetes, and 37% were diagnosed with diabetes (5% with type 1 diabetes and 32% with type 2 diabetes). Remarkably, only one-third of women initially diagnosed with GDM maintain normal glucose tolerance afterwards(Reference Damm, Houshmand-Oeregaard and Kelstrup3).
In general, dietary guidelines for pregnant women align with those for the general healthy population, except for a few differences, such as the need to address common micronutrient deficiencies that often coexist in women of childbearing age(Reference Haider and Bhutta4,Reference Keats, Haider and Tam5) . The energy requirements of pregnant women with diabetes depend on many factors, including weight, height and physical activity, and are similar to those of non-pregnant women of similar age but consider the additional requirements that occur during pregnancy(Reference Araszkiewicz, Bandurska-Stankiewicz and Borys6,Reference ElSayed, Aleppo and Aroda7) . Dietary components have significant and clinically relevant effects on blood glucose modulation(Reference Russell, Baka and Björck8). Gestational hyperglycaemia increases the risk of complications both in the mother and in the developing foetus. It can also negatively affect the future development of the child. Treatment should be aimed at achieving the same blood glucose levels that are typical for healthy pregnant women(Reference ElSayed, Aleppo and Aroda7).
Several scientific societies have developed dietary recommendations for GDM. A summary of such recommendations presented by the International Federation of Gynecology and Obstetrics(Reference Hod, Kapur and Sacks9), the Endocrine Society(Reference Blumer, Hadar and Hadden10), the American College of Obstetrics and Gynecologists(11), the National Institute for Health and Care Excellence(12), Diabetes Canada(Reference Feig, Berger and Donovan13), the American Academy of Nutrition and Dietetics(Reference Duarte-Gardea, Gonzales-Pacheco and Reader14) and the American Diabetes Association (ADA)(Reference ElSayed, Aleppo and Aroda7) can be found in a report by Mustad et al.(Reference Mustad, Huynh and López-Pedrosa15). The general recommendations of scientific societies emphasise that nutritional therapy for patients with GDM based on a healthy, personalised diet should maintain the desired glycaemic control, prevent excessive weight gain and reduce the risk of large-for-gestational-age (LGA) babies. This is especially important in women with obesity and a history of macrosomia(Reference Pintaudi, Fresa and Dalfrà16). It is recommended that carbohydrate (CHO) intake be increased to at least 175 g/d. Recommendations confirm the need to consume foods with low glycaemic indexes (GIs) and high fibre contents and avoid sugary foods and sugary drinks. It can be concluded that the methodological quality of GDM guidelines varies(Reference Mustafa, Hofer and Harding17) and that they need constant updating(Reference Zhang, Zhou and Zhong18). The energy demand of an average woman is approximately 35 kcal per kg of ideal body weight. In pregnant women who are overweight, it should be approximately 25–30 kcal per kg of body weight. Yang et al.(Reference Yang, Tian and Zhang19) recommended varied energy intake based on pre-pregnancy body mass index (BMI).
Excessive energy contained in the foods consumed by pregnant women contributes to excessive maternal and foetal weight gain(Reference Goldstein, Abell and Ranasinha20,Reference Kurtzhals, Nørgaard and Secher21) . To avoid this, the Institute of Medicine (IOM) elaborated guidelines for recommended weight gain for pregnant women(Reference Rasmussen, Catalano and Yaktine22,Reference Rasmussen and Yaktine23) . The recommendations take into account the negative impact of both excessive and insufficient gestational weight gain (GWG) on maternal–foetal outcomes.
Overweight and obesity, which are diagnosed before pregnancy(Reference Black, Sacks and Xiang24), as well as excessive GWG, in addition to hyperglycaemia, are associated with foetal hypertrophy in patients with GDM. The main macronutrient is maternal glucose, which promotes the growth of the foetus and placenta. In women with GDM, long-term hyperglycaemia and the presence of several amino acids, such as arginine or leucine, increase the risk of developing hyperinsulinaemia.
Weight gain is the main determinant of an increase in energy requirements during pregnancy. The metabolic changes occurring during pregnancy (anabolic state in the first two trimesters and maternal catabolism in the third trimester) contribute to a gradual increase in energy requirements. In the second half of pregnancy, the foetus grows rapidly, increasing basal metabolism by 60%(Reference Parrettini, Caroli and Torlone25). Ferraro et al.(Reference Ferraro, Contador and Tawfiq26) showed, on the basis of available studies, that excessive weight gain increases the risk of other complications during pregnancy and has long-term effects on the health and weight of both mothers and children.
The optimal ranges of weight gain during pregnancy are difficult to determine and have limited predictive value(Reference Voerman and Santos27,Reference Viecceli, Remonti and Hirakata28) . The recommended values of GWG for both underweight and obese pregnant women are the subject of lively debate. The scientific community often expresses different opinions on this issue depending on the ethnicity or region of origin of the pregnant woman(Reference Robillard, Dekker and Boukerrou29–Reference Xu, Ge and Bi32). There is a vital need to revise the current recommendations and establish a specific linear or curvilinear relationship for the optimal GWG in each geographic or ethnic region(Reference Barnes, Wong and Ross33,Reference Ohadike, Cheikh-Ismail and Ohuma34) .
Currently, various dietary modifications have been proposed to reduce the risk of GDM, ensure adequate GWG and limit the increase in postprandial blood glucose levels, consequently improving perinatal outcomes.
A number of studies presenting various management methods for the abovementioned clinical conditions are discussed below.
Search strategy and selection criteria
We searched for reports published within the past 10 years in journals indexed in PubMed (clinical study, clinical trial, meta-analysis, randomised controlled trial, systematic review) and the Cochrane Library (Cochrane Reviews) using major search terms such as ‘diet and gestational diabetes’, ‘diet and risk of gestational diabetes’, ‘nutrition in gestational diabetes’ and ‘treatment for GDM’, and in addition to the above terms, we searched for systematic reviews using the following keywords: ‘Mediterranean dietary patterns’, ‘DASH diet’, ‘dietary patterns’, ‘risk of progression to type 2 diabetes’, ‘carbohydrate intake’, ‘diet acidity’, ‘soft drink consumption’, ‘fried foods’, ‘polyphenols and flavonoids’, ‘plant diets’, ‘vegetarian diet’ and ‘vitamin D and gestational diabetes’. We focused on original scientific papers, randomised controlled trials (RCT), cohort studies, and systematic reviews and meta-analyses of RCT assessing the effects of diet on GDM risk, the natural history of GDM and the effects of modified dietary interventions in women with GDM on perinatal outcomes. We excluded articles reporting studies on the pathophysiology of GDM, the diagnosis of GDM, other diseases related to GDM, the assessment of only the impact of physical activity on GDM, glucose monitoring in GDM, and dietary intervention accompanied by the use of hypoglycaemic drugs or insulin in GDM. Reports were also excluded due to topics of interest, such as environmental pollution, types of diabetes other than GDM, treatment costs, bariatric surgery, animal experiments, studies based on various criteria for diagnosing GDM and so on. To provide a comprehensive synthesis of the literature, we included both individual RCT as well as systematic reviews and meta-analyses. While systematic reviews offer aggregated evidence, individual RCT allow a detailed examination of study characteristics, heterogeneity and recent developments that may not yet be captured in systematic reviews or meta-analyses. We have not eliminated observational studies from the search results. However, observational data are prone to unexplained confounding. These findings should be interpreted with caution, and confirming the findings of such studies in the results of meta-analyses and RCT is desirable.
The analysis of the results of the conducted search aims to provide insights into effective dietary interventions for the prevention and treatment of GDM. The search strategy and flow diagram of this review are shown in Supplementary Table S1 and Figure 1. According to this diagram, duplicates were eliminated during the abstract screening. Then, the coauthors independently conducted eligibility analysis to select articles pertaining to the topic of the review, which included different types of dietary interventions in women at risk of GDM or with GDM. The coauthors agreed on the final list of articles by consensus.
Flow diagram of the review.
All studies that we found in our search are cited in the Results section to assess the available research results as objectively as possible. The synthesis of results included analyses of the impact of different diets, dietary components, supplements and implementations of dietary intervention on the risk of developing GDM, the course of pregnancy and perinatal outcomes in GDM, and the risk of developing T2DM in women diagnosed with GDM.
Diet and the risk of developing GDM
Diet is one of the main elements of a healthy lifestyle affecting the course of pregnancy and the risk of GDM.
Dietary components and supplements
Dietary components
Schoenaker et al.(Reference Schoenaker, Mishra and Callaway35) reviewed a number of observational studies on diets to reduce the risk of GDM. In conclusion, the current guidelines are justified and, most importantly, effective. These guidelines include reducing foods containing saturated fatty acids and cholesterol (that is, reducing red meat and egg consumption) and following a diet rich in vegetables, fruits, legumes, low-fat dairy products, whole grains, nuts and fish. The effects of the consumption of certain nutrients, such as white bread, added sugars, legumes, fish and butter, are correlated with glucose intolerance in pregnant women(Reference Yuste Gómez, Del Pilar Ramos Álvarez and Bartha36). An increased risk of GDM is associated with increased pre-pregnancy consumption of meat, especially red and processed meat, and haem iron intake(Reference Marí-Sanchis, Díaz-Jurado and Basterra-Gortari37). Talebi et al. demonstrated with high certainty a significant association between dietary animal protein intake and the risk of GDM by conducting an analysis of seventeen prospective cohort studies with a total of 49 120 participants. In addition, on the basis of the data obtained, they reported that higher intake of total protein, total meat and red meat increases the risk of GDM(Reference Talebi, Ghoreishy and Ghavami38). The consumption of animal protein both before pregnancy and during pregnancy is significantly associated with the occurrence of GDM(Reference Tabaeifard, Moradi and Arzhang39). Hajhashemy et al. reported a significant association between total protein intake and GDM, which was dose dependent for both animal and plant protein intake(Reference Hajhashemy, Bagherniya and Sadeghi40). Chronic and excessive consumption of ultra-processed foods is associated with an increased risk of GDM(Reference Talebi, Mehrabani and Ghoreishy41). A higher risk of GDM also occurs with a high intake of cholesterol (≥300 mg/d). Gao and Cui(Reference Gao and Cui42) reported a linear relationship between dietary cholesterol intake, haem iron (≥1·1 mg/d), red and processed meat (1 serving/d gain) and eggs (≥7 per week) and GDM risk. Moreover, the authors highlighted that every pregnant woman should be individually assessed for her nutritional needs so that the quantities and ratios of individual food groups may be determined.
However, data on factors that may increase the risk of progression from GDM to T2DM are still limited(Reference O’Reilly, Leonard and Dasgupta43). The analysis included 21 prospective cohort studies involving 191 589 participants, including 12 331 women with GDM. The consumption of animal meat and fast food is associated with an increased risk of developing GDM, with total risk ratios (RR) of 1·35 (95% CI 1·16, 1·57) and 1·75 (95% CI 1·41, 2·19), respectively(Reference Quan, Zeng and Jiao44). Eating an ultra-processed food-rich diet(Reference Paula, Patriota and Gonçalves45), that is, a Western eating pattern characterised by high consumption of red meat, processed meat, fried foods and refined grains, may increase the risk of GDM (RR 1·27; 95% CI 1·03, 1·56)(Reference Marí-Sanchis, Díaz-Jurado and Basterra-Gortari37,Reference Hassani Zadeh, Boffetta and Hosseinzadeh46) . Frequent consumption of meat or processed meat and protein from animal sources and potatoes increases the risk of GDM(Reference Gao and Cui42,Reference Mijatovic-Vukas, Capling and Cheng47) . In addition, the regular consumption of fried fish and fried chicken has been found to be associated with an increased risk of GDM(Reference Osorio-Yáñez, Gelaye and Qiu48).
Greater consumption of sugar-sweetened soft drinks before pregnancy has been shown to be another independent risk factor for GDM(Reference Donazar-Ezcurra, Lopez-del Burgo and Martinez-Gonzalez49,Reference Nicolì, Prete and Citro50) . A plant-based diet plays a crucial role in reducing the risk of GDM. In a study conducted by Chen et al.(Reference Chen, Qian and Liu51), the authors followed 20 707 pregnancies over a 10-year period, documenting 846 cases of GDM. They indicated that greater adherence to a healthy plant-based diet before pregnancy is associated with a lower risk of GDM. A similar association was found in the case of plant-based eating patterns, with high levels of whole grains, fruits, vegetables and low-fat dairy intake(Reference Hassani Zadeh, Boffetta and Hosseinzadeh46). In addition, a higher intake of flavonoids, polyphenols and fruits was also associated with this pattern(Reference Gao, Zhong and Zhou52). Various eating patterns that emphasise the consumption of plant-based foods may have beneficial effects on glycaemic control(Reference Schiattarella, Lombardo and Morlando53) and potentially reduce the risk of GDM(Reference Raghavan, Dreibelbis and Kingshipp54). Excessive consumption of fruits, potatoes and fruit juices may be associated with an increased risk of GDM(Reference Li, Xie and Zhang55). The evidence for dietary intervention to prevent the development of GDM is summarised in Supplementary Table S2.
Supplements
Low levels of vitamin D in the blood increase the risk of GDM, especially in overweight and obese women(Reference Palacios, Kostiuk and Peña-Rosas56). However, numerous studies have not shown whether vitamin D supplementation has any effect on the risk of GDM(Reference Zhang, Gong and Xue57) or showed no statistical significance(Reference Bao, Song and Bertrand58). There are also reports, based on the analysis of numerous works, that vitamin D supplementation in pregnant women is important for reducing the risk of GDM(Reference Irwinda, Hiksas and Lokeswara59,Reference Suárez-Varela, Uçar and Peraita-Costa60) .
Compared with placebo, supplementation with vitamin D + calcium ions (one trial; very low-quality evidence) and supplementation with omega-3 fatty acids during pregnancy (twelve studies involving 5235 women; high-quality evidence) did not result in the expected benefits of reducing the risk of GDM(Reference Griffith, Alsweiler and Moore61).
The dietary or supplemented intake of myo-inositol during pregnancy has been the subject of numerous studies. These studies demonstrated a beneficial effect on reducing the risk of GDM, such as the meta-analyses reported in Refs. (Reference Griffith, Alsweiler and Moore61–Reference Li and Shi65).
Importantly, the increased risk of GDM may be associated with reduced vitamin C intake during pregnancy(Reference Zhou, Liu and Zhou66).
The use of probiotics, as shown in the SPRING Double-Blind Randomized Controlled Trial, did not prevent GDM in overweight and obese pregnant women(Reference Callaway, McIntyre and Barrett67). However, probiotics may be effective in reducing the risk of gestational diabetes in women with a lower BMI and at a younger age(Reference Li, Zhang and He68). Masulli et al. and Shahriari et al.(Reference Masulli, Vitacolonna and Fraticelli69,Reference Shahriari, Karimi and Shahriari70) examined the effect of probiotic supplementation during pregnancy and did not find a reduced risk of GDM. Moreover, studies suggest that there is an increased risk of preeclampsia when probiotics are administered(Reference Chu, Yan and Zhang71,Reference Davidson, Barrett and Price72) . The effects of the supplements on preventing the development of GDM are summarised in Supplementary Table S3.
Dietary acid load
Diets rich in animal protein and poor in fruits and vegetables have a greater content of acid precursors than base precursors. Diets with high acid-forming potential may increase the risk of T2DM. A high load of dietary acidity leads to impaired insulin sensitivity and increases the risk of GDM(Reference Zhao, Zhou and Lei73).
The dietary acid load (DAL) or food acid load assessment is estimated by two(Reference Hernandez, Van Pelt and Anderson74) or three different formulas(Reference Zhao, Zhou and Lei73) to quantify the potential renal acid load (PRAL), net endogenous acid production (NEAP) and animal fat (A) to potassium (P) ratio (A:P ratio).
$${\rm{PRAL}}\left( {{\rm{mEq}}/{\rm{d}}} \right) = \left( {0\cdot4888 \times {\rm{protein }}\left( {{\rm{g}}/{\rm{d}}} \right)} \right) $$$+ \left( {0\cdot0366 \times {\rm{P }}\left( {{\rm{mg}}/{\rm{d}}} \right)} \right) $$$- \left( {0\cdot0205 \times {\rm{K}}\left( {{\rm{mg}}/{\rm{d}}} \right)} \right)$$$- \left( {0\cdot0263 \times {\rm{Mg }}\left( {{\rm{mg}}/{\rm{d}}} \right)} \right) $$$- \left( {0\cdot0125 \times {\rm{Ca}}\left( {{\rm{mg}}/{\rm{d}}} \right)} \right),$$
$${\rm{NEAP}}\left( {{\rm{mEq}}/{\rm{d}}} \right) = 54\cdot5 \times {\rm{protein}}\left( {{\rm{g}}/{\rm{d}}} \right)/{\rm{K}}\left( {{\rm{mEq}}/{\rm{d}}} \right) - 10\cdot2,$$
$${\rm{A}}\!\!:\!\!{{{\rm P} \;{\rm ratio}}} = {\rm{animal \, protein }}\left( {{\rm{g}}/{\rm{d}}} \right)/{\rm{K}}\left( {{\rm{g}}/{\rm{d}}} \right),$$
The load of dietary acid causes an increase in fasting blood sugar, HbA1c, total cholesterol and low-density lipoprotein cholesterol (LDL-C) and a greater risk of developing GDM(Reference Saraf-Bank, Tehrani and Haghighatdoost75). The evidence regarding the impact of dietary acidity on the increased risk of developing GDM is summarised in Supplementary Table S4.
Selected diets
Mediterranean diet (MedDiet), Dietary Approaches to Stop Hypertension (DASH) and Alternative Healthy Eating Index (AHEI)
Many studies have shown that the Mediterranean diet (MedDiet) used before and in early pregnancy reduces the risk of GDM(Reference Hassani Zadeh, Boffetta and Hosseinzadeh46,Reference Al Wattar, Dodds and Placzek76–Reference Xu, Wang and Bian79) , especially if it contains extra virgin olive oil and pistachios(Reference Melero, García De La Torre and Assaf-Balut80–Reference Waugh, Pencheva and Woolner82). Even the use of this diet in early nutritional intervention at 8–12(Reference Zaragoza-Martí, Ruiz-Ródenas and Herranz-Chofre81) or 12–14(Reference Assaf-Balut, de la Torre and Fuentes83) weeks of gestation reduces the incidence of GDM. De la Torre et al.(Reference de la Torre, Assaf-Balut and Jiménez Varas84) suggested that the implementation of early nutritional intervention with a MedDiet could become a widely used therapy to reduce the occurrence of GDM. Greater adherence to the MedDiet can reduce the risk of GDM by approximately 36%(Reference Jafari Nasab, Ghanavati and Clark85). Mijatovic-Vukas et al.(Reference Mijatovic-Vukas, Capling and Cheng47) analysed 40 of the 1167 articles that met the established inclusion criteria. These authors reported that diets such as the MedDiet, Dietary Approaches to Stop Hypertension (DASH) and the Alternative Healthy Eating Index (AHEI) were associated with a 15–38% reduction in the relative risk of GDM. Gao et al.(Reference Gao, Zheng and Jiang86) analysed a total of nineteen studies involving 108 084 participants to assess the effects of diets such as the MedDiet, DASH and AHEI and the overall index of a plant-based diet on the risk of GDM. All these diets used before and during pregnancy reduce the risk of developing GDM. The evidence of the effectiveness of the MedDiet, DASH and AHEI diets in reducing the risk of developing GDM is summarised in Supplementary Table S5.
Low-GI diet
Markovic et al.(Reference Markovic, Muirhead and Overs87) compared the effects of a low-GI diet and a conventional high-fibre diet on pregnancy outcomes, birth weight z scores and maternal metabolic profiles in women at high risk of GDM. The group consisted of pregnant women (between 12 and 20 weeks of gestation) with at least one of the following risk factors: over 35 years of age, family history of T2DM, GDM during previous pregnancies, birth weight of more than 4 kg and high risk of diabetes. At enrolment, GDM was diagnosed in 15% of pregnant women, and an additional 14% met the diagnostic criteria for GDM at the beginning of the third trimester. In summary, the authors concluded that both dietary regimens had similar effects on the course of pregnancy and the birth parameters of the neonates. Notably, no differences in the incidence of GDM were observed. On the basis of a review of thirteen studies involving 39 720 pregnant women, Zhang Y et al. reported no significant association between GI and GDM but reported a relationship between glycaemic load (GL) and the risk of GDM(Reference Zhang, Feng and Li88).
A Cochrane Library review(Reference Tieu, Shepherd and Middleton89) presented data on the impact of dietary interventions on reducing the risk of GDM during pregnancy and on the overall health of mothers and their babies. The analysis included eleven RCT involving a general population of 2786 women and their children. Another review compared the use of low-GI and moderate-GI diets(Reference Vitagliano, Saccone and Cosmi62). Both reviews revealed no differences with respect to the risk of GDM. However, the quality of the available data was rather low. Notably, a study conducted on a small group of women with GDM (131 women) revealed that the use of a personalised, hypoenergetic, low-glycaemic and low-fat diet early in pregnancy prevents the occurrence of GDM in women with a BMI ≥25 kg/m2(Reference Bruno, Petrella and Bertarini90). The evidence of the effectiveness of the low-GI diet in reducing the risk of developing GDM is summarised in Supplementary Table S6.
Low-carbohydrate diet
The longstanding recommendations for a low-CHO diet with a relatively high fat content lack comprehensive documentation(Reference Hernandez, Van Pelt and Anderson91). The Nurses Health Study II tracked 867 cases of GDM pregnancies over a 10-year follow-up period and revealed that relatively low CHO intake alongside high fat and protein contents can increase the risk of GDM(Reference Bao, Bowers and Tobias92). A higher risk of GDM is associated with low CHO intake and increased protein intake(Reference Zhou, Chen and Zhong93). An analysis of the dietary patterns of 1455 women indicated an increased risk of GDM when they consumed foods rich in animal fat and protein during the first trimester of pregnancy(Reference Dong, Sun and Cai94). Liberalising complex CHO intake while reducing fat consumption helps to achieve glycaemic targets and reduces postprandial free fatty acid (FFA) levels(Reference Hernandez, Van Pelt and Anderson74). The evidence of the effectiveness of the low-CHO diet in reducing the risk of developing GDM is summarised in Supplementary Table S7.
Prenatal lifestyle interventions, diet and exercise
In pregnant women, diet and daily physical activity of mild-to-moderate intensity may be useful therapeutic approaches to improve glycaemic control and prevent the onset of GDM. Body weight and BMI gains in the period before pregnancy are associated with GDM(Reference Najafi, Hasani and Izadi95,Reference Zhang, Wang and Xu96) . It remains unclear what foods should be recommended during the period before pregnancy(Reference Cui, Liao and Xu97). The questions are when to start lifestyle interventions in women to reduce the risk of GDM and whether the intervention, as shown in the work of Song et al., is most effective up to the 15th week of gestation(Reference Song, Li and Leng98). Many interventions have been proposed to prevent the occurrence of GDM. However, data from twenty-three studies analysed in a systematic review and network meta-analysis by Wu et al. in 2022 revealed that dietary interventions, as well as combined diet and exercise, do not provide significant benefits in GDM prevention(Reference Wu, Jin and Hu99). This finding was also observed earlier, for example, in an RCT conducted by Sahrakorpi et al. (Reference Sahrakorpi, Rönö and Koivusalo100). Similar conclusions were presented by Bain et al.(Reference Bain, Crane and Tieu101) on the basis of the evaluation of thirteen RCT. However, physical activity and dietary interventions significantly reduce excessive weight gain.
The DALI lifestyle study was conducted in antenatal clinics across eleven centres in nine European countries(Reference Simmons, Devlieger and Van Assche102). While following a healthy diet and increasing physical activity helped to reduce GWG, it did not significantly improve fasting or post-load glucose levels, insulin concentrations or homeostatic model assessment for insulin resistance (HOMA-IR) values. Meanwhile, numerous studies have reported positive effects of diet and exercise on the risk of GDM(Reference Lin, Yang and Zhang103). Conclusions from RCT involving 8918 women and 8709 infants, mostly from high-income countries, suggest a reduced risk of GDM after dietary and physical activity interventions during pregnancy compared with standard care (moderate-quality evidence)(Reference de la Torre, Assaf-Balut and Jiménez Varas84,Reference Shepherd, Gomersall and Tieu104) . The positive effects of diet and exercise on the prevention of GDM were demonstrated in a paper by Koivusalo et al.(Reference Koivusalo, Rönö and Klemetti105). The authors reported that the incidence of GDM was reduced by 39%. However, this effect was affected by BMI and region.
There are different strategies for dietary interventions in studies leading to GWG reduction and prevention of GDM in overweight and obese women. However, these strategies do not allow adequate distinction of the components of beneficial dietary interventions(Reference Lamminpää, Vehviläinen-Julkunen and Schwab106). Intensifying the diet and modifying exercise in early pregnancy can prevent the onset of GDM in overweight or obese women. However, behavioural intervention in these pregnant women is not always sufficient(Reference Poston, Bell and Croker107). A diet and moderate-intensity exercise for 50–60 min can lead to a reduction in GDM occurrence of approximately 24% when exercise is performed twice a week. This percentage increases to 35% when exercise is performed three times a week(Reference Guo, Shu and Fu108). Overall, on the basis of systematic Cochrane reviews, it can be concluded that, compared with standard care, a combination of diet and exercise may reduce the risk of developing GDM (RR −0·85; 95% CI 0·71, 1·01)(Reference Griffith, Alsweiler and Moore61).
Research on the consumption of a diet rich in polyphenols is a good example of the difficulty of assessing the effect of diet on GDM risk(Reference Jorquera, Fornes and Cruz109). Five studies devoted to this topic reported a significant, inverse association between polyphenol-rich diet intake and GDM, whereas five other studies reported no association and two reported a positive association(Reference Pham, Do and Lee110). Apparently, other factors influenced the results of these studies, and the diet applied was not a decisive determinant of GDM risk reduction.
Analysis of the results of observational studies (based on thirty qualifying meta-analyses) suggests that increased BMI and hypothyroidism show the strongest consistent evidence for an association with the onset of GDM(Reference Giannakou, Evangelou and Yiallouros111). Recently, the development of information technologies has enabled interventions in the field of mobile healthcare. He et al., on the basis of sixteen RCT involving 7351 participants, reported that mHealth-based lifestyle interventions had a beneficial effect on the prevention of GDM in overweight and obese pregnant women(Reference He, Huang and He112). The evidence of the effectiveness of prenatal lifestyle interventions, diet and exercise on the risk of developing GDM is summarised in Supplementary Table S8.
Diet in the management of GDM
GDM is associated with adverse maternal and neonatal outcomes. Nutrition has a significant effect on the results of GDM treatment. To prevent the exposure of the foetus to hyperglycaemia effectively, procedures that do not allow excessive weight gain in mothers are implemented. Normal-weight women who gain weight before pregnancy represent a population at high risk of perinatal complications(Reference Timmermans, Oosterman and Spaanderman113). According to a pooled meta-analysis of twenty-five cohort studies conducted as part of the LifeCycle Project(Reference Voerman and Santos27), the risk of adverse reactions in mothers and infants varies according to pre-pregnancy weight and weight gain during pregnancy. In particular, obese mothers, who have high weight gain during pregnancy, are most vulnerable to pregnancy complications(Reference Santos, Voerman and Amiano114).
Nutritional interventions for managing foetal growth
Risk of macrosomia
The potential benefits of controlling weight gain during pregnancy after a diagnosis of GDM have been the subject of many studies(Reference Peaceman, Clifton and Phelan115,Reference Poolsup, Suksomboon and Amin116) . Controlling weight gain during pregnancy through lifestyle modifications following a proper diet is considered a first-line treatment. Studies have shown a relationship between high GWG or low GWG and the occurrence of adverse events in women and infants. Excessive foetal weight is partly due to genetic predispositions and partly due to disrupted CHO metabolism. Weight gain occurs and is the norm of a healthy pregnancy, but excessive weight gain can contribute to poor outcomes for both the baby and the mother. Weight gain is associated with an increase in energy demand during pregnancy.
Dietary intervention to prevent excessive weight gain
Excessive weight gain in pregnant women with GDM results in increased chances of macrosomia and LGA and an increased likelihood of gestational hypertension(Reference Egan, Dennedy and Al-Ramli117). Although research suggests that appropriate dietary treatment and physical activity during pregnancy may lead to adequate control of weight gain(Reference Muktabhant, Lawrie and Lumbiganon118), interventions do not significantly prevent the adverse effects of pregnancy(Reference Aiken, Hone and Murphy119–Reference Mitanchez, Ciangura and Jacqueminet121). The effectiveness of lifestyle change intervention studies is mostly low, which is explained by poor patient compliance(Reference Rogozińska, Zamora and Marlin122). There are a few barriers that pregnant women face, which make controlling weight gain during pregnancy difficult(Reference Dodd, Deussen and Louise123,Reference Vanstone, Kandasamy and Giacomini124) . A proper diet and increased physical activity in women with GDM significantly reduce foetal growth(Reference Mitanchez, Ciangura and Jacqueminet121). Teede et al.(Reference Teede, Bailey and Moran125) analysed a total of 117 randomised trials (including 67 with GDM) of clinical prenatal interventions associated with lifestyle changes, that is, diet and exercise. A diet with physical activity was associated with a reduction in GWG (−1·35 kg; 95% CI −1·95, −0·75) and total adverse maternal outcomes. There are reports that an appropriate diet and physical activity improve postprandial glycaemic control in women with GDM. However, glycaemic control does not affect maternal or neonatal outcomes(Reference Allehdan, Basha and Asali126). The use of dietary treatment had a greater effect on reducing GWG than did physical activity alone(Reference Teede, Bailey and Moran125). Even after being diagnosed with GDM (often at 28 weeks of pregnancy), it is not too late to make lifestyle changes(Reference Aiken, Hone and Murphy119). While lifestyle changes during pregnancy may be helpful in reducing excessive GWG, the benefits do not translate into most pregnancy outcomes(120,Reference Mitanchez, Ciangura and Jacqueminet121) . Therefore, defining the optimal diet, including the optimal energy content, remains an unresolved issue.
Reducing the intake of added sugars to prevent excessive GWG is one of the primary recommendations for women with GDM. Therefore, the use of artificial sweeteners, which usually replace caloric sweeteners, is worth mentioning. Conway et al. reported that approximately one-third of pregnant women consumed low-calorie sweeteners. Frequent use of sweeteners requires research primarily to determine their impact on maternal and child health outcomes(Reference Conway, Cawley and Geraghty127).
Despite many works, the importance of eating low-calorie meals and reducing GWG remains a topic of discussion. Notably, Feng et al.(Reference Feng, Zhao and Fu128), on the basis of six RCT in women with GDM, did not find any benefit of using a diet with limited energy intake compared with a standard diet, in terms of both maternal and neonatal outcomes. Data obtained from twenty-three RCT (4990 women) assessing the reduction in GWG caused by lifestyle modifications during pregnancy had a statistically insignificant effect on reducing the incidence of GDM(Reference Ruifrok, Van Poppel and Van Wely129). One clinical trial registry and three Chinese databases revealed that interventions to reduce excessive GWG lead to a small reduction in infant birth weight and macrosomia risk(Reference Bennett, Walker and Blumfield130). Therefore, there is still a need to define the ideal range of weight gain, which has not yet been established(Reference Sun, Juan and Xu131). Undoubtedly, the establishment of guidelines aimed at appropriate control of GWG is limited by the high methodological variability of dietary interventions(Reference Flynn, Dalrymple and Barr132).
The analysis of sixteen RCT by Yamamoto et al.(Reference Yamamoto, Kellett and Balsells133) revealed the importance of modifications of dietary interventions in pregnant women with GDM, which consequently led to a reduction in the birth weight of infants. An important element in preventing the occurrence of complications during pregnancy and childbirth is the use of individualised nutritional intervention(Reference Li, Wang and Wang134). The evidence on the effectiveness of dietary intervention to prevent excessive weight gain during pregnancy in women with GDM is summarised in Supplementary Table S9.
The question remains as to whether additional modifications are possible within the established principles of the composition of the diet to prevent adverse maternal and foetal effects resulting from GDM. Many reports have investigated the effects of the diet used after the diagnosis of GDM on perinatal outcomes.
Low birth weight and small for gestational age
Many risk factors can be considered causes of LBW and small for gestational age (SGA). For example, compared with an omnivorous diet, a vegetarian diet increases the risk of LBW in babies(Reference Tan, Zhao and Wang135). Low maternal haemoglobin levels (<110 g/l) are associated with poor birth outcomes, that is, low birth weight, preterm birth and SGA(Reference Young, Oaks and Tandon136).
Children and adolescents with a history of SGA have a 2·33-fold greater risk of developing T2DM than do children or adolescents born with the appropriate weight for gestational age(Reference Martín-Calvo, Goni and Tur137). Dietary treatment to reduce excessive GWG does not affect the risk of LBW or SGA(Reference Bennett, Walker and Blumfield130). Evidence of the impact of dietary treatment on LBW and SGA in newborns of women with GDM is summarised in Supplementary Table S10.
Carbohydrates, vitamins and probiotics
Total carbohydrate intake
It is not clear whether there is an adequate nutritional strategy in GDM that allows complete normalisation of maternal and foetal outcomes. Different modifications of the diet are proposed to limit the surge in postprandial glycaemia and to ensure correct body weight gain. We can distinguish two main nutritional approaches. The first approach recommends reducing total CHO intake to 33–40% of total energy intake (EI), which is supposed to lead to a reduction in postprandial glycemia and the risk of macrosomia. The second approach is to use higher CHO intake (60–70% of EI) containing high-quality CHO sources with a lower GI, which may also result in better maternal glycaemic control. A low-CHO diet improves some pregnancy outcomes, results in a lower incidence of LGA and lowers HbA1c levels(Reference Lin, Zhang and Meng138).
In two intervention studies in which low-CHO diets were compared with control diets (CHO contents of 40–45% and 55–60% of EI, respectively), no differences were observed in the frequency of caesarean sections, the frequency of insulin use or the incidence of neonatal macrosomia(Reference Viana, Gross and Azevedo139). One review evaluating thirteen studies, cited two studies and reported that a diet with a low glycaemic load may reduce the risk of macrosomia(Reference Wong, Yuen-Man Chan and Ng140).
An analysis of reports comparing the results of low-CHO and high-CHO diets revealed no significant differences in high gestational age, perinatal mortality, maternal hypertension or the frequency of caesarean section(Reference Han, Middleton and Shepherd141).
Overall, systematic reviews and meta-analyses of multiple RCT do not allow us to determine which diet used in women with GDM has the most beneficial effect on the health outcomes of women and their children (Supplementary Table S11).
Vitamins and probiotics used as dietary supplements
Vitamins and probiotics are often used as dietary supplements. The following question remains: which vitamins are worth using during pregnancy?
Studies have focused mainly on assessing the health outcomes of vitamin D supplementation during pregnancy(Reference Morales-Suárez-Varela, Uçar and Soriano142). Observational studies and RCT have shown that blood levels of vitamin D in women with GDM are lower than those in control women(Reference Zhang, Gong and Xue57). An inverse association was found between 25(OH)D levels and the risk of preeclampsia(Reference Morales-Suárez-Varela, Uçar and Soriano142–Reference Zhao, Zhou and Wang144) and gestational hypertension(Reference Zhao, Zhou and Wang144). However, Pérez-López et al.(Reference Pérez-López, Pasupuleti and Mezones-Holguin145), Bialy et al.(Reference Bialy, Fenton and Shulhan-Kilroy146) and Gallo et al.(Reference Gallo, McDermid and Al-Nimr147) reported that vitamin D supplementation had no effect on the occurrence of preeclampsia. On the basis of a Cochrane review by Palacios et al., which has previously presented other conclusions(Reference Palacios, De-Regil and Lombardo143), supplementation with 601 IU/d to 4000 IU/d vitamin D during pregnancy may have little or no effect on the risk of preeclampsia(Reference Palacios, Kostiuk and Peña-Rosas56). However, the latest update of this review concluded that this evidence is very uncertain(Reference Palacios, Kostiuk and Cuthbert148).
In a study published by Asemi et al. (Reference Asemi, Karamali and Esmaillzadeh149), women with GDM received capsules containing 50 000 IU of vitamin D3 twice – once at the start of the study and again on day 21 of the intervention. This led to improved glycaemic control, a reduction in total cholesterol and LDL-C, and decreased maternal polyhydramnios and infant hyperbilirubinaemia. In another work, vitamin D supplementation was shown to significantly reduce fasting plasma glucose and regulate HOMA-IR(Reference Jin, Sha and Dong150). In a meta-analysis conducted by Akbari et al.(Reference Akbari, Mosazadeh and Lankarani151), the authors reported that the use of vitamin D supplements was associated with improvements in LDL-C and insulin sensitivity as well as an increase in HOMA-B. However, there was no effect on the levels of fasting plasma glucose, insulin, HbA1c, triacylglycerol (TG), total cholesterol or HDL-C. Recently, a study was published that included the results of twenty RCT involving 1682 patients with GDM, of whom 837 received vitamin D supplementation. The results of this meta-analysis present well-documented data that vitamin D supplementation in pregnant women with GDM can lower total serum cholesterol, LDL-C and TG levels and increase HDL-C levels. More importantly, vitamin D supplementation reduces maternal hyperbilirubinaemia, neonatal hyperbilirubinaemia and the risk of hospitalisation(Reference Wu, Song and Wang152). A meta-analysis based on nineteen RCT with 1550 participants suggested that supplementation of GDM women with vitamin D leads to improved glycaemic control and a reduction in adverse maternal–neonatal outcomes(Reference Wang, Chen and Hu153). Notably, a review of six studies involving 456 women revealed no moderate-to-high-quality evidence of the benefits of vitamin D supplementation in women with GDM(Reference Rodrigues, Lima and Da Silvia Mazeto154). The evidence from many studies does not allow the determination of the unequivocal benefits of vitamin D supplementation in pregnancy(Reference Yang, Chitale and O’Callaghan155). Additional randomised, rigorous, high-quality and larger studies evaluating the results of vitamin D supplementation in pregnancy are still needed(Reference Palacios, Kostiuk and Peña-Rosas56).
Usually, vitamin E is administered together with zinc or magnesium. The administration of vitamin E and magnesium improved glycaemic control and lipid profiles(Reference Maktabi, Jamilian and Amirani156). The administration of omega-3 fatty acids and vitamin E to women with GDM favourably affects glycaemic control and serum TG, VLDL-C and HDL-C levels but has no effect on LDL-C levels(Reference Taghizadeh, Jamilian and Mazloomi157). Other authors also showed that omega-3 fatty acid supplementation in combination with vitamin D or E in women with GDM had no effect on total cholesterol, preterm birth or macrosomia >4000 g(Reference Jiang, Gao and Yan158).
Supplementation with probiotics may contribute to a significant increase in insulin sensitivity(Reference Okesene-Gafa, Moore and Jordan159–Reference Taylor, Woodfall and Sheedy161), which may affect glucose metabolism and weight gain in pregnant women with GDM(Reference Dolatkhah, Hajifaraji and Abbasalizadeh162). Studies investigating the effects of probiotic supplements containing Bifidobacterium and Lactobacillus in women with GDM have examined their use for 4 weeks at the end of the second and beginning of the third trimester. These studies revealed a decrease in fasting glucose and an increase in insulin sensitivity(Reference Kijmanawat, Panburana and Reutrakul163). In addition, Asgharian et al.(Reference Asgharian, Homayouni-Rad and Mirghafourvand164) reported, in a small study group, that supplementation with probiotics does not significantly reduce the risk of GDM or other effects in mothers and infants but can improve glucose metabolism in overweight and obese pregnant women. However, in another study, an intervention involving the administration of Lactobacillus salivarius UCC118 in women with GDM had no effect on glycaemic control(Reference Lindsay, Brennan and Kennelly165).
The benefits of using probiotic and symbiotic supplements in women with GDM were evaluated on the basis of the published results of twelve RCT involving 894 participants(Reference Zhou, Ding and Wu166). The results revealed, among other effects, improved glucose and lipid metabolism and a reduced risk of foetal macrosomia and foetal hyperbilirubinaemia. Other authors, on the basis of an analysis of 843 articles, came to similar conclusions(Reference Yefet, Bar and Izhaki167). Lactobacillus acidophilus LA-5, Bifidobacterium BB-12, Streptococcus thermophilus STY-31 and Lactobacillus delbrueckii bulgaricus LBY-2 contained in one probiotic capsule may affect several biomarkers of inflammation and oxidative stress(Reference Hajifaraji, Jahanjou and Abbasalizadeh168). However, taking them does not affect the birth weight of the newborn(Reference Wang, Tung and Chang169). Cosupplementation in women with GDM may have a beneficial effect on a number of parameters determining the metabolic state. For example, cosupplementation with vitamin D and probiotics leads to a reduction in TGs and VLDL-C(Reference Jamilian, Amirani and Asemi170). Evidence for the effects of vitamins and probiotics used as dietary supplements on the health outcomes of women with GDM and their children is summarised in Supplementary Table S12.
Selected diets
Low-GI diet
The results of many studies suggest that a low-GI diet may have a positive effect on metabolic control parameters, such as 2-h postprandial and fasting glucose concentrations(Reference Hu, Tan and Jin171,Reference Xu and Ye172) . No significant effect of a low-GI diet on HbA1c, birth weight or macrosomia was found in women with GDM(Reference Xu and Ye172). In a study assessing cardiometabolic and inflammatory parameters, the effects of a low-GI diet on the lipid profile in patients with GDM were not consistent(Reference Ojo, Ojo and Wang173). A low-GI diet led to a reduction in the number of patients with GDM requiring insulin(Reference Sanpawithayakul, Kaewprasert and Tantiyavarong174,Reference Wei, Heng and Gao175) . A systematic review and meta-analysis of RCT evaluating maternal diets conducted by Viana et al. revealed that a low-GI diet reduced the proportion of patients using insulin and lowered the birth weight of newborns compared with a control diet(Reference Viana, Gross and Azevedo139). Low-GI diets can have a beneficial effect on overweight and obese mothers with high glucose levels(Reference Zhang, Han and Chen176). However, dietary consultations conducted for this group of women did not reveal a difference in the IR of the mother or newborn compared with the standard pregnancy diet consultation(Reference Zhang, Wang and Yang177). In conclusion, the effects of a low-GI diet on pregnancy outcomes continue to be debated(Reference Lin, Zhang and Meng138). Compared with a healthy eating (HE) diet, a low-intensity dietary intervention with a low-GI diet during pregnancy did not result in any significant differences in birth weight, foetal percentile, ponderal index (neonatal equivalent of BMI)(Reference Moses, Price and Quinn178) or macrosomia(Reference Xu and Ye172). Mohd Yusof et al.(Reference Mohd Yusof, Firouzi and Mohd Shariff179) did not find that a low-GI diet had a beneficial effect on glycaemic control and improved pregnancy outcomes in women with GDM. However, Wei et al.(Reference Wei, Heng and Gao175) reported that low-GI diets reduce the risk of macrosomia on the basis of an analysis of five studies with 302 women with GDM. Evidence for the effects of a low-GI diet on the health outcomes of women with GDM and their children is summarised in Supplementary Table S13.
DASH and Mediterranean diets
The DASH diet is designed for people with hypertension and diabetes. The DASH diet is a healthy eating plan that includes the consumption of whole grains, low-fat dairy products, fruits and vegetables, as well as lower amounts of saturated fats and refined grains, with a total of 2400 mg of sodium per day(Reference Asemi, Samimi and Tabassi180). Researchers reported that following the DASH guidelines resulted in a reduction in insulin levels(Reference Li, Gan and Chen181) and fasting glucose(Reference Ha, Bonner and Jadoo182). Another study reported a decrease in HOMA-IR and an increase in total plasma antioxidant capacity (TAC) and total glutathione (GSH)(Reference Asemi, Samimi and Tabassi180). Compared with those on the control diet, infants born to mothers on the DASH diet had significantly lower weights, head circumferences and weight indices. The DASH diet also significantly reduced the number of pregnant women with GDM starting insulin therapy(Reference Asemi, Samimi and Tabassi180) and the incidence of macrosomia(Reference Zhang, Wang and Tashiro183) and caesarean sections(Reference Li, Gan and Chen181). In a Cochrane Library review, Han et al.(Reference Han, Middleton and Shepherd141) analysed the impact of various dietary recommendations for pregnant women with diabetes on the course of pregnancy and the health of neonates. The analysis included the combined results of nineteen RCT conducted with an overall population of 1398 patients. A few diets differing in GI, CHO, unsaturated fatty acid, fibre and soy protein contents were compared. The DASH diet was compared with the control diet. In summary, the available data on the impact of various types of dietary interventions on the health of pregnant women with diabetes and their children are ambiguous, with the exception of the potential effect of the DASH diet on the reduced incidence of caesarean sections.
The Effect of Simple, Targeted Diet in Pregnant Women with Metabolic Risk Factors on Pregnancy Outcomes (ESTEEM) group showed that a simple, individualised MedDiet in pregnant women with metabolic risk factors did not reduce the overall risk of unwanted complications in the mother and offspring but could reduce weight gain during pregnancy(Reference Al Wattar, Dodds and Placzek76). A GDM prevention study at St. Carlos also revealed that MedDiet-based intervention reduced the incidence of GDM and several adverse maternal–foetal outcomes, that is, emergency caesarean section, perineal trauma and urinary tract infections(Reference Assaf-Balut, de la Torre and Fuentes83). Thus, adherence to the MedDiet during pregnancy is beneficial to both mothers and offspring(Reference Melero, García De La Torre and Assaf-Balut80,Reference Jafari Nasab, Ghanavati and Clark85,Reference Amati, Hassounah and Swaka184) . Moreover, MedDiet-based intervention in the early stages of pregnancy has a beneficial effect on mothers’ health after delivery(Reference Melero, Arnoriaga and Barabash185). Evidence for the effects of the MedDiet and DASH diet on the health outcomes of women with GDM and their children is summarised in Supplementary Table S14.
Other diets
Hernandez et al.(Reference Hernandez, Van Pelt and Anderson74,Reference Hernandez, Van Pelt and Anderson91) evaluated a diet rich in CHOs with a reduced supply of fats (CHO/protein/fat ratio 65%/20%/15%) in women with GDM and obesity (BMI of 34 ± 1·0 kg/m2). This diet enabled satisfactory glycaemic control, as determined by continuous glucose monitoring in the subcutaneous tissue, while lowering postprandial FFA levels. The diet improved insulin sensitivity in mothers and reduced obesity in neonates.
A diet potentially beneficial for dietary management in pregnant patients with diabetes is the CHOICE diet, that is, choosing healthy options in carbohydrate energy. While most of the research has focused on the importance of glycaemia affecting foetal growth, it should be noted that FFA and TG also contribute to foetal fat storage. The CHOICE diet involves replacing 20% of fat calories with more complex, better CHOs, resulting in CHO-to-fat and CHO-to-protein ratios of 60% to 25% and 15%, respectively. Data from a crossover RCT revealed that a CHOICE diet with a higher complex CHO content and lower fat content than a conventional diet (∼40% CHO, 45% fat and 15% protein) achieved a similar glycaemic profile with continuous glucose monitoring (6% higher with CHOICE) and significantly lower FFA levels after a meal(Reference Hernandez, Van Pelt and Anderson91).
The increased consumption of polyunsaturated fatty acids may be beneficial for the foetus and the course of GDM(Reference Wang, Jiang and Yang186). However, comparisons of the effects of a diet rich in unsaturated fats with those of a diet low in unsaturated fats revealed no clear differences with respect to LGA, preeclampsia, the prevalence of hypertension during pregnancy or the number of caesarean sections(Reference Han, Middleton and Shepherd141). The effect of a fast-food diet, with a relatively high content of saturated fats and simple CHOs, on obesity in newborns remains to be determined(Reference Barbour, Farabi and Friedman187).
In 2021, Schiattarella et al.(Reference Schiattarella, Lombardo and Morlando53) reviewed the works published on the impact of plant-based diets on the course of GDM. In conclusion, they reported that plant-based diets contribute to better metabolic control and have a positive effect on the onset of GDM. Moreover, the authors emphasise the need for further research, especially RCT. A diet rich in total fruits, whole fruits, vegetables, greens and beans, vegetable proteins, whole grains, dairy and total protein is a better-quality diet that improves glycaemic control in women with GDM(Reference Gadgil, Ehrlich and Zhu188).
Recently, an increasing number of pregnant women have been following vegetarian diets. The effect of a vegetarian diet on the course of pregnancy is still debated. Tan et al. conducted a meta-analysis of nineteen observational studies. An association was found between pregnancy in women on vegetarian diets and low birth weight (LBW), but it should be emphasised that it was marginally significant(Reference Tan, Zhao and Wang135). Importantly, however, eight studies conducted in different countries with a total of 72 284 participants revealed that following a strict vegetarian diet during pregnancy was associated with an increased risk of SGA babies and LBW(Reference Papadopoulou, Sarantaki and Metallinou189). Evidence for the effects of the abovementioned diets on the health outcomes of women with GDM and their children is summarised in Supplementary Table S15.
Telemedicine supporting women with GDM
In recent years, an increasingly important role has been played by telemedicine interventions, which can more effectively lower the glycemia of pregnant women with GDM(Reference Zhang, Wang and Yang177,Reference Adesina, Dogan and Green190–Reference Park, Lee and Cho199) . Smartphone apps can help women with GDM not only better control their blood glucose levels, lowering HbA1c, fasting blood glucose and 2-h postprandial blood glucose, but also favourably affect the course of pregnancy and reduce the risk of complications(Reference Eberle, Loehnert and Stichling200–Reference Xie, Dai and Qin203). Technology-supported lifestyle interventions during pregnancy have the potential to improve treatment outcomes, but there are still too few data on their effectiveness(Reference O’Brien, McCarthy and Gibney204,Reference El Seifi, Younis and Ibrahim205) . However, there are reports that an app itself does not have to yield the desired results. Rasekaba et al.(Reference Rasekaba, Furler and Young206) reported that telemedicine support could help women with GDM achieve proper glycaemic control faster, but their clinical outcomes did not differ from those of pregnant women with GDM in regular care. An RCT in Norway aimed at supporting women with GDM by providing comprehensive information on GDM, a healthy diet, exercise and glycaemic control did not show the expected impact on the clinical results(Reference Borgen, Småstuen and Jacobsen207). No differences were found in birth weight, breastfeeding pattern, obstetric complications or frequency of admittance to the neonatal intensive care unit between the control group and the neonatal intensive care unit(Reference Borgen, Småstuen and Jacobsen207). Counselling and active behavioural interventions to achieve adequate GWG can reduce the risk of sudden caesarean section, macrosomia and LGA(Reference Cantor, Jungbauer and McDonagh208). However, counselling on increasing CHO intake over several meals and snacks, limiting simple sugar intake and increasing fibre intake spanning intervention from pregnancy to one year after delivery did not result in significant differences in comparison with the control group regarding delivery, as did neonatal, anthropometric or psychobehavioural outcomes one year after delivery(Reference Horsch, Gilbert and Lanzi209). In the RTC conducted by Kytö et al., continuous glucose monitoring, with a periodic mobile app (eMOM) with self-tracking of glucose and nutritional advice, did not improve birth outcomes in women with GDM(Reference Kytö, Hotta and Niinistö198). Therefore, future research should focus on identifying the most important smartphone app features that improve GDM management. A summary of the effectiveness of the use of telemedicine in supporting the treatment of patients with GDM is presented in Supplementary Table S16.
Risk of type 2 diabetes mellitus
Women diagnosed with GDM have an increased risk of developing T2DM(Reference Tandon, Gupta and Kapoor210). However, the risk varies by ethnicity(Reference Wambua, Singh and Okoth211). In the United States, T2DM can occur in approximately 50% of women 10 years after being diagnosed with GDM(Reference Stith, Buls and Keim212). In Canada, diabetes is diagnosed in approximately 20% of this population 9 years after delivery(Reference Chaudhry, Doyle and Nerenberg213). On the basis of these reports and a few meta-analyses(Reference Vounzoulaki, Khunti and Abner214,Reference Juan, Sun and Wei215) , the risk of developing T2DM after GDM is highly variable. Further analysis is needed to link the risk factors leading to T2DM and the type of intervention(Reference O’Reilly, Leonard and Dasgupta43,Reference Dennison, Ward and Griffin216) .
Women with GDM require information about how to continue dietary treatment after childbirth and about the need to maintain a healthy lifestyle, thus reducing the risk of progressing to T2DM. Lifestyle changes yield the best results in stopping or delaying T2DM progression. A fundamental study in this area was the Diabetes Prevention Program (DPP)(217). Although this programme did not include the benefits associated with its implementation before and during pregnancy, later research by Ferrara et al. (Reference Ferrara, Hedderson and Brown218,Reference Ferrara, Hedderson and Albright219) and Hu et al. (Reference Hu, Tian and Zhang220) revealed that the use of the dietary methodology, which was adapted from the DPP curriculum, reduced postpartum weight retention and increased the intensity of physical activity. However, the estimation of the risk of prediabetes and diabetes did not reach statistical significance. Women with a history of GDM who are overweight and obese before pregnancy and who have subsequent weight retention after childbirth (≥5 kg) have an increased risk of dysglycaemia after childbirth(Reference Chen, Soh and Tint221). Interventions that lead to lifestyle changes during pregnancy do not eliminate the risk of postpartum diabetes. However, these interventions 3 years after delivery can reduce the risk of diabetes(Reference Li, Yang and Cui222). A short-term 3-year follow-up in women with a history of normal fasting plasma glycaemia revealed that, in the Mediterranean lifestyle group, 34·1% of women were diagnosed with fasting glucose disorders or impaired glucose tolerance (prediabetes), that is, less often than in the control group, where it was diagnosed in 43·2% of cases(Reference Pérez-Ferre, Del Valle and Torrejón223). In summary, interventions aimed at changing lifestyles, a healthy lifestyle and healthy diets can lead to a reduced risk of T2DM(Reference Bellou, Belbasis and Tzoulaki224–Reference Winkler Pedersen, Terkildsen Maindal and Juul226). However, preventative actions do not always have the desired effect, depending on the method of intervention(Reference Gilinsky, Kirk and Hughes227–Reference Wang, Wei and Guo229).
Not all dietary recommendations are easy to implement. A good example to consider is the recommendation to limit the consumption of potatoes, which, in many countries, are the main plant food and an important source of CHO in the diet. Although potatoes provide certain vitamins (for example, vitamin C), macronutrients (for example, potassium) and fibres, they are mainly composed of starch with a high GI. In studies conducted in the United States, greater weight gain and a greater risk of T2DM have been reported in men and women who consumed more potatoes, even after adjusting for diabetes risk factors, including BMI. The meta-analysis, which included a total of nineteen studies (thirteen for T2DM and six for GDM), revealed a significant association between potato consumption and the risk of T2DM(Reference Guo, Zhang and Jiang230).
Moreover, longer and exclusive lactation is a process that should be taken into account in the prevention of T2DM in women with previous GDM(Reference Feng, Xu and Hu231,Reference Tanase-Nakao, Arata and Kawasaki232) . The evidence regarding the risk of developing T2DM after GDM in relation to lifestyle interventions is summarised in Supplementary Table S17.
Discussion
Risk factors for GDM and preventive strategies
There are many risk factors for GDM. These include advanced maternal age, overweight or obesity, family history of diabetes, previous GDM, birth of a macrosomic child, ethnicity and smoking(Reference Zhang, Rawal and Chong233). In addition to these known risk factors for GDM, new diagnostic tools that could be used in the future to identify women with GDM are needed(Reference Rodrigo and Glastras234). Conducting extensive educational campaigns promoting pregnancy planning in women at risk of GDM with the implementation of appropriate nutritional treatment may lead to an improvement in the fate of many women and children. First, women at risk for GDM should be persuaded to eat a healthy diet(Reference Cui, Liao and Xu97). To give up high consumption of red meat, processed meats, fried foods and refined grains, individuals should be encouraged to increase their intake of high-fibre foods, which consequently reduces the risk of GDM(Reference Qiu, Liu and Zhu235). The effects of total fat, animal fat, vegetable fat, dietary cholesterol and omega-3 fatty acids on an increased risk of GDM have been reported(Reference Talebi, Zeraattalab-Motlagh and Rahimlou236). Importantly, highly processed foods and drinks are associated with a more pro-atherosclerotic, insulin-resistant metabolic profile(Reference Millar, Harrington and Perry237). Women who are overweight or obese should take measures to lose weight before pregnancy. Excess maternal body weight in the pre-pregnancy period increases the risk of pregnancy complications(Reference Lewandowska, Więckowska and Sajdak238). As already mentioned, the effects of three diets, that is, the MedDiet, DASH and AHEI, are associated with a reduction in the relative risk of GDM(Reference Gao, Zheng and Jiang86). Similar benefits can be obtained by using ‘plant-based’ eating patterns with high levels of whole grains, fruits(Reference Chen, Qie and Quan239), vegetables and low-fat dairy consumption(Reference Chen, Qian and Liu51). In addition, regular exercise can help prevent the onset of GDM. Counselling that focuses on presenting the benefits of increased physical activity, the consumption of vegetables, fruits, a low-carbohydrate/low-sugar diet and a higher-quality diet may reduce the risk of developing GDM(Reference Sampathkumar, Parkhi and Ghebremichael-Weldeselassie240). However, it is important to recognise that there is still a need for high-quality testing of women planning for pregnancy to assess both clinical outcomes and adherence(Reference Davies, Mullin and Chapman241).
Although supplementation with probiotics may improve glucose metabolism in overweight and obese pregnant women(Reference Xu, Fu and Pan242,Reference Kim, Keogh and Clifton243) , it does not significantly reduce the risk of GDM(Reference Callaway, McIntyre and Barrett67) or other outcomes in mothers or infants(Reference Asgharian, Homayouni-Rad and Mirghafourvand164). Moreover, micronutrient deficiencies negatively affect the health of the mother and the outcome of pregnancy. Supplementation with micronutrients can have numerous benefits, affecting perinatal results, but their mass use, due to the possibility of side effects, should be discouraged. Usually, several micronutrient deficiencies are responsible for side effects. Thus, supplementing only one deficiency will not be very effective(Reference Santander Ballestín, Giménez Campos and Ballestín Ballestín244).
On the basis of the literature examining the impact of dietary interventions on the risk of GDM, the available data are insufficient to identify a single effective dietary approach. These include low- or moderate-GI diets, low- or high-carbohydrate diets, diets high in saturated fats and those recommended for caloric restriction(Reference Martis, Crowther and Shepherd245,Reference Donazar-Ezcurra, López-Del Burgo and Bes-Rastrollo246) .
The challenge of a universal dietary strategy for GDM
There is no universal dietary strategy to achieve normoglycaemic values in women with GDM. The use of low-GI or DASH diets, which have numerous metabolic benefits(Reference Akhlaghi247), did not significantly affect pregnancy outcomes compared with adherence to general recommendations for healthy eating. The ADA(Reference ElSayed, Aleppo and Aroda7) takes the position that there is no one-size-fits-all eating pattern for people with diabetes and recommends individualisation when planning an appropriate diet. The proportions of calories obtained from CHO, fat and protein cannot be the same for all people with diabetes. The distribution of macronutrients should consider metabolic goals, preferences and individualised analysis of current dietary patterns. The need to individualise the diet also results from interindividual differences in glycaemic changes after the same foods are eaten, which is associated with the different compositions of the intestinal microflora(Reference Zeevi, Korem and Zmora248). Moreover, the composition of the intestinal microflora changes during pregnancy and influences metabolic control(Reference Ferrocino, Ponzo and Gambino249–Reference Schoonakker, Van Peet and Van Den Burg251). These observations open the possibility of changing the composition of the microbiota with a properly selected diet or modifying the diet according to the specific composition of the gut microbiota to prevent or better control GDM(Reference Ponzo, Fedele and Goitre250).
Nutritional therapy as the primary treatment for GDM
Nutritional therapy is the main treatment for GDM(Reference Dolatkhah, Hajifaraji and Shakouri252). Currently, there is a consensus on the need to improve glucose metabolism in pregnant women with GDM, determine the composition of the diet, eat low-fat healthy foods and prevent excessive accumulation of foetal fat. However, the current knowledge about macronutrients and their optimal quality and quantity in the diets of women with GDM is still insufficient(Reference Moreno-Castilla, Mauricio and Hernandez253). There are still questions raised in the publication of Ludwig et al.(Reference Ludwig, Hu and Tappy254), which require answers about the effect of reducing total CHO consumption, the role of a low-CHO diet, sweeteners, the long-term effect of various types of CHO, the effect of increased consumption of resistant starch and the effect of ketosis. In conditions of nutrient deficiency (for example, with a sharp reduction in calories in the diet and limiting CHO intake for fear of implementing insulin therapy), ketone bodies secure the development of the embryonic brain. However, this adaptation can also have a negative effect on foetal development, since maternal hyperketonaemia is associated with an increased incidence of foetal malformations, neurophysiological developmental disorders and stillbirth(Reference Zeng, Liu and Li255). Therefore, preventing ketosis during pregnancy is very important(Reference Herrera256).
In an article published by Moses and Cefalu(Reference Moses and Cefalu257), the authors summarised a series of reports aimed at establishing the proper management of pregnant women diagnosed with GDM while identifying questions that require further consideration. The diet used to achieve the best results during pregnancy may differ from that recommended for healthy people, which raises doubts as to whether these changes have an impact on long-term health effects. On the basis of integrated data from fourteen intervention studies and two observational studies, Gilbert et al.(Reference Gilbert, Gross and Lanzi258) suggested that diet interacts not only with physical activity but also with psychosocial wellbeing. Close cooperation with a doctor is extremely important for patients with GDM(Reference Modzelewski, Stefanowicz-Rutkowska and Matuszewski259). Currently, there are insufficient data on a single dietary intervention that should be prescribed to women diagnosed with GDM(Reference Moreno-Castilla, Mauricio and Hernandez253,Reference Egan, Enninga and Alrahmani260) .
In T2DM, the use of vegetarian, vegan, Mediterranean and DASH diets leads to an average decrease in HbA1c of 0·8%, a decrease in fasting glucose and an improvement in insulin sensitivity(Reference De Carvalho, Dias-Vasconcelos and Santos261). However, vegetarianism may increase the risk of having babies with low birth weights(Reference Tan, Zhao and Wang135).
Obese women or those who have achieved the recommended GWG should use limited energy. In those with pre-pregnancy morbid obesity (BMI ≥35 kg/m2), GWG below 5 kg during pregnancy can prevent macrosomia, foetal hypertrophy and hypertension(Reference Barquiel, Herranz and Meneses262).
The relationships between GWG and pregnancy outcomes tend to be positive for insufficient GWG but negative for excessive GWG(Reference Xie, Liu and Pujol263). An appropriate education programme on nutrition and physical activity can lead to proper weight gain and lower rates of gestational hypertension, preeclampsia and large gestational neonatal rates in obese pregnant women(Reference Barquiel, Calvo and Moreno-Domínguez264). However, the evidence for the advantage of a restricted-energy diet over a standard diet does not allow us to draw clear conclusions(Reference Lamminpää, Vehviläinen-Julkunen and Schwab106). Even significant dietary restrictions can be accepted if the medical team provides adequate and convincing information about likely benefits(Reference McParlin, Hodson and Barnes265). An important issue is choosing a diet suitable for pregnant women with GDM, which can improve health outcomes in both women and infants. The dietary advice needed to achieve health goals varies and does not allow one to choose the best diet(Reference Han, Middleton and Shepherd141). Notably, inconsistent nutritional counselling can create barriers to appropriate health interventions(Reference Chaudhry, Doyle and Nerenberg213,Reference Martis, Brown and McAra-Couper266) . Personal food preferences should also be taken into account when making dietary recommendations(Reference Hui, Sevenhuysen and Harvey267).
On the basis of the knowledge accumulated thus far, it can be concluded that dietary intervention in women with GDM is beneficial for the health of mothers and children. However, there is a gap in the literature that leaves open the question of which specific diet to choose that will bring health benefits, will not harm the environment, will not be expensive and will gain social acceptance(Reference Pérez-Ferre, Del Valle and Torrejón223,Reference Li, Grewal and Hinkle268) .
The need for high-quality research
Many clinical interventions have involved a limited number of subjects, including Asemi et al.(Reference Asemi, Samimi and Tabassi180), D’Arcy et al.(Reference D’Arcy, Rayner and Hodge225) and Callahan et al.(Reference Callahan, Schneider-Worthington and Martin269). The evaluation of the quality of the evidence by Yamamoto et al.(Reference Yamamoto, Kellett and Balsells133) revealed that studies with relatively few participants significantly reduced the reliability of the comparison of diets. Given the prevalence of GDM, there is an urgent need for new studies involving larger study groups to ensure appropriate statistical power while investigating the effects of potential nutritional interventions in women with GDM(Reference Pan, Pan and Chen160).
Strengths and limitations
In this review, we focused on peer-reviewed, published literature to ensure the inclusion of high-quality studies that have undergone rigorous methodological assessment and editorial oversight. We searched for reports published within the past 10 years in journals indexed in PubMed and the Cochrane Reviews. The inclusion of additional databases, grey literature, conference abstracts and theses could enhance the comprehensiveness of our review, but the quality of such sources is at least less certain. There were also technical difficulties in including outputs from other databases. For example, in Google Scholar, source publications are not divided into research articles, review articles and so on. Grey literature, including conference abstracts and theses, was not considered because such sources often lack full methodological details, making it challenging to critically appraise their quality and reliability. Given that our objective was to evaluate the effectiveness of dietary interventions for the prevention and management of GDM and their impact on perinatal outcomes, we prioritised sources of studies that warrant robust methodologies that provide clear, reproducible and clinically applicable findings. Most importantly, the number of articles retrieved from PubMed and the Cochrane Library already provided an extensive body of evidence, allowing us to demonstrate that it is difficult to draw unambiguous conclusions regarding the superiority of individual dietary modifications, including low-GI or DASH diets, over general nutritional guidelines for women diagnosed with GDM in relation to pregnancy outcomes and offspring health.
Several narrative, systematic and umbrella reviews have examined dietary interventions in women at risk of GDM or patients with GDM. However, previous reviews have typically analysed these two groups separately. By contrast, our review provides a comprehensive analysis of both populations, assessing whether the effectiveness of individual diets differs between them. Furthermore, given the rapid advancement of research in this field, our methodology of including the state of the art in the introduction and discussion and basing the results on a search of studies published in the past 10 years provides the most up-to-date and relevant answers to the questions posed in the title of the manuscript.
Notably, there are also several limitations in the interpretation of the presented research results. Given the lack of a clear glycaemic threshold, from which the risk of GDM increases, non-uniform criteria for the recognition of GDM, no data on metabolic control during dietary intervention, heterogeneity of dietary interventions (micronutrient content, lack of data on micronutrient intake), often short follow-up periods, and lack of data on the characteristics of women before and during pregnancy (for example, BMI, GWG) exist. Only in a small percentage of publications is it possible to obtain information about adherence to medical recommendations. However, this does not rule out the basic conclusions of the work regarding the role of dietary intervention before and during pregnancy.
Conclusions
On the basis of the studies available thus far, it is difficult to draw unambiguous conclusions regarding the superiority of individual dietary modifications, including low-GI or DASH diets, over the general guidelines for proper nutrition in women after the diagnosis of GDM in relation to the course of pregnancy and the health of offspring. Choosing the right diet to maintain proper metabolic control in women with GDM is still difficult and requires an individualised approach. Although pooled analyses of several RCT conducted thus far have clearly shown that modified dietary interventions benefit maternal metabolic control and birth weight in GDM, more prospective studies are needed. There are currently no convincing data on what type of diet significantly reduces the risk of GDM complications. One can only conclude that there is no universal diet strategy for women with GDM. Nevertheless, studies concerning dietary interventions before pregnancy clearly indicate that the initiation of dietary treatment should be promoted as much as possible when planning pregnancy, especially in women with risk factors for GDM. Such a strategy should reduce the occurrence of GDM and facilitate its treatment when, despite prophylactic treatment before pregnancy, it is not possible to achieve normoglycaemia during pregnancy.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0954422425100103.
Authorship
Conceptualisation: J.K. and D.W. Methodology, validation, investigation, writing – original draft preparation: J.K., D.W. and P.L. Formal analysis: J.K. Data curation: J.K. and P.L. Writing – review and editing, resources, supervision, project administration: P.L.
Financial support
This research received no specific grant from any funding agency, commercial or not-for-profit sector.
Declaration of interests
The authors declare none.
