Discussion

This study thoroughly investigated the impact of dietary factors on cancer mortality and DALY, along with the regional specificity of each factor’s impact. The findings revealed a decreasing trend in cancer burden attributable to dietary factors from 1990 to 2019, while the number of deaths and disability-adjusted life years increased due to population growth and longer human lifespan. Key groups affected were the elderly aged 65 and men. The top three dietary risk factors contributing to the cancer burden were diets low in whole grains, milk, and calcium, predominantly found in the High middle SDI region, particularly in Southern Latin America, Central Europe, and Western Sub-Saharan Africa. Effective dietary pattern optimization in these regions necessitates a concerted effort led by local governments, in partnership with international health agencies such as the World Health Organization. Policy makers must prioritize comprehensive nutritional guidelines and enforce regulations that curb the availability of unhealthy food options. Empirical evidence from studies like He, Jenner, and MacGregor^{(Reference He, Li and MacGregor21)} on the impact of modest salt reduction on blood pressure underscoreds the beneficial role of engaging community leaders to promote healthier eating habits and enhance local dietary regulations.

In 2019, the age-standardized death and DALY rates for cancer were approximately 5·5 %. This could be largely attributed to dietary factors, highlighting the importance of promoting a healthy diet to alleviate the burden of cancer. We identified three key contributors to cancer mortality and DALY rates: low intake of whole grains, low intake of milk, and cancer-related physiological and biological factors. Numerous meta-analysis studies have shown that higher consumption of whole grains is associated with a reduced risk of cancer in various specific areas such as the colon, stomach, pancreas, breast, esophagus, brain, and oral cavity. Additionally, dose-response analyses have indicated that a daily intake of 30 grams of whole grains could decrease the risk of cancer death by 7 %^{(Reference Gaesser22)}. Notably, regions with higher SDI values tend to have lower whole grain intake and higher cancer mortality and DALY rates^{(Reference Murray23)}. The low intake of whole grains is particularly prominent in Central Europe and Southern Latin America, where it is a significant risk factor for cancer^{(Reference Gaesser24)}. Increased health awareness has sometimes led to the adoption of low-carb or gluten-free diets, which may inadvertently reduce whole grain intake, despite dietary guidelines recommending whole grains. Urbanization, nutritional transitions, changing dietary habits, and increasing health awareness are some of the factors contributing to the lower consumption of whole grains in these regions^{(Reference Popkin25)}. Interestingly, as SDI values increase, the burden of cancer stabilizes, but then decreases as SDI values approach 0·78 before rising again. Southern Latin America exhibited a turning point in cancer burden when the SDI value reached 0·6, after which it began to decline. Overall, the low intake of whole grains may be linked to various factors such as urbanization, dietary transitions, changing habits, and increased health consciousness^{(Reference Murphy, Asiki and Ekoru26,Reference Allen, Williams and Townsend27)} .

The presence of vitamin D, calcium, lactoferrin, conjugated linoleic acid, butyric acid, and lactose in milk provides certain anti-cancer properties^{(Reference Barrubés, Babio and Becerra-Tomás28)}. Inadequate intake of vitamin D and calcium is a significant risk factor for various cancers^{(Reference Peterlik, Grant and Cross29)}. Regions with low milk and calcium consumption exhibit higher cancer mortality rates, with Southern Latin America having the lowest milk intake and Southern Asia having the lowest calcium intake. As the SDI increases, the burden trend in Southeast Asia remains relatively stable. It is recommended that healthy adults under the age of 60 consume 1000 milligrams of calcium per day, with higher values for the elderly^{(Reference Peterlik, Grant and Cross29)}. Evidence suggests that calcium deficiency is not only common in the elderly but also in young individuals^{(Reference Barrett-Connor30)}, particularly in Southern Latin America and Southeast Asia where low calcium intake is prevalent^{(Reference Deng, Wei and Zhai31)}. Addressing the issue of low calcium intake is crucial for improving nutritional quality and promoting cancer prevention through dietary control.

Through visual comparison of bar charts, it could be observed that the age-standardized mortality rate and DALY rate of cancer attributed to dietary risk factors are higher in males than in females. Additionally, the age at which cancer deaths peak is higher in females compared to males. The influence of diet on cancer risk may be linked to the protective impact of estrogen^{(Reference Van Cromphaut, Rummens and Stockmans32)}. Following a comprehensive analysis of dietary factors, significant sex disparities persist. Dietary habits, particularly in males, show higher intake of red and processed meat, while females exhibit higher consumption of milk, dairy products, and calcium due to various complex interactions^{(Reference Al-Hazzaa, Abahussain and Al-Sobayel33)}. While low calcium intake may contribute to higher cancer rates in older individuals^{(Reference Barrett-Connor30)}, it is not likely to be the only factor. Other age-related biological changes and cumulative risk factors must also be considered. Therefore, providing effective and appropriate dietary guidance for the elderly is crucial, as they may find it more challenging to make dietary changes.

Regions with high SDI values tend to have higher consumption of red and processed meat, leading to an increased burden of cancer. Red meat and processed meat are favored for their sensory qualities and cultural significance, with meat consumption on the rise globally^{(Reference Lovegrove and Hobbs34)}. However, emerging research indicates that red meat could generate carcinogens like N-nitrosamines, polycyclic aromatic hydrocarbons, or nitrites during various cooking or processing methods^{(Reference Bingham, Pignatelli and Pollock35,Reference Lund, Wharf and Fairweather-Tait36)} . Compared to populations with the lowest red and processed meat intake, those with the highest consumption experienced a 23 % and 29 % increase in all-cause mortality, respectively^{(Reference Larsson and Orsini37)}. Processed meat, in particular, contains high levels of sodium and nitrites^{(Reference Micha, Michas and Mozaffarian38)}, reducing its intake could help manage sodium consumption. In regions with medium SDI region, the cancer burden linked to dietary risks is primarily due to excessive sodium intake. Despite a notable reduction in cancer burden associated with high sodium intake across regions from 1990 to 2019, East Asia and Andean Latin America continue to have elevated salt consumption, highlighting the urgent need for shifts in health concepts and dietary habits. Conversely, in low and medium-low SDI regions, the cancer burden from dietary risks is mainly attributed to low fruit and vegetable intake. The cancer-fighting potential of consuming ample fresh fruits and vegetables is well-documented due to their fiber, vitamins, minerals, and antioxidants^{(Reference Azeem, Gillani and Siddiqui39)}. The availability and affordability of fruits and vegetables play a crucial role in determining consumption levels, necessitating support from national policies, regulations, taxation, and regional coordination^{(Reference Micha, Khatibzadeh and Shi40,Reference Headey and Alderman41)} .

When comparing cancer mortality across regions, it’s important to account for not only cancer risk factors but also other competing causes of death and their associated risks. Mongolia bears the highest cancer burden, while Egypt and the Syrian Arab Republic have the lowest burden. This disparity could be attributed to the dietary practices prevalent in these countries. Mongolia’s nomadic diet is characterized by high meat consumption, inadequate food preservation and refrigeration facilities, potential excessive salt intake, low consumption of fruits and vegetables, and frequent alcohol consumption, all of which are potential cancer risk factors^{(Reference Sandagdorj, Sanjaajamts and Tudev42)}. Egypt’s notably low cancer rates may be linked to a diet rich in high-fiber foods, beans, and green vegetables^{(Reference Platz, Giovannucci and Rimm43,Reference Tantamango, Knutsen and Beeson44)} . Their consumption of protein and fat falls below Western standards, with a majority of protein derived from plant sources and a significant portion of the diet comprising fiber^{(Reference Abou-Zeid, Khafagy and Marzouk45)}. While the identification and adoption of healthier dietary patterns are integral to overall healthy lifestyle choices, they may partially explain the reduced cancer risk observed in these regions. Dietary habits are deeply intertwined with cultural practices and specific factors unique to each country^{(Reference Grosso, Bella and Godos46)}. Governments, in collaboration with public health organizations and community leaders, are responsible for guiding these changes through the implementation of health promotion campaigns, nutritional education programs, and policy regulations tailored to cultural contexts.

If a country struggles to change its dietary patterns, it is crucial to prioritize population-wide dietary adjustments to lessen the burden of cancer. Effective policy interventions that have been successful in other contexts include Norway’s taxation on sugar-sweetened beverages, Japan’s national dietary guidelines which emphasize the consumption of n-3 fatty acids and seafood^{(Reference O’Connor47)}, and Brazil’s government-led campaigns to promote fruit and vegetable consumption^{(Reference Huang, Pomeranz and Wilde48)}. This study offers a detailed analysis of cancer mortality and DALY rates attributed to dietary factors between 1990 and 2019 using GBD data to highlight regional disparities in cancer burden from dietary factors. However, the study faces several limitations that suggest areas for further research. Firstly, the potential interactions between dietary risk factors might lead to underestimation or overestimation of their impacts. Future studies should explore the independence and interdependence of these factors using more localized datasets. Secondly, the limitations in the modeling methods of the GBD2019 database highlight the need for developing more refined models that could accurately reflect the nuances of dietary impacts on different cancer types. Thirdly, although adjustments were made for confounding factors like age and sex, future research should consider the effects of other potential confounders such as socioeconomic status and genetic predispositions, particularly in longitudinal cohort studies.

The cancer burden attributable to dietary factors exhibited a declining trend from 1990 to 2019. Globally, inadequate consumption of whole grains, milk, and calcium emerged as the primary risk factors for cancer. Regionally, the High SDI region has been reducing red and processed meat consumption, the Middle SDI region is focusing on limiting sodium intake, and the Low SDI region is emphasizing increased consumption of vegetables and fruits. Specific recommendations include increasing whole grains intake in Central Europe, boosting milk intake in Southern Latin America, and enhancing calcium intake in Southeast Asia. Urgent attention is needed in the Southern Latin America region and Mongolia to establish healthier dietary patterns. Targeting elderly and male populations is crucial in addressing specific dietary needs. A thorough evaluation of the impact of various dietary risk factors on cancer burden can offer valuable insights to inform individual dietary choices, cancer prevention strategies, and health policy development.