Discussion

Given the limitations associated with the measurement of food intake, we aimed to determine the reproducibility of a food menu that includes a large variety of meal-type foods, beverages and snacks (sixty-two items in total) in order to measure total energy and macronutrient intakes during breakfast, mid-morning and lunch for three ILS and three OLS. We hypothesised that the energy and macronutrient intakes over several meals (two meals and snacks over 5 h) would be reproducible in men and women. The present results show no significant differences in our three ILS and three OLS as well as for the combination of these six sessions, as far as EI and macronutrient intakes are concerned. No significant interactions were noted between sex and experimental sessions for EI, carbohydrate and dietary fat intakes, while a significant interaction was found for protein intake between sexes over time. We also reported a good ICC and a relatively good CVws for total EI, while the reproducibility for macronutrient intake, especially dietary fat, was lower. Food items on the menu were overall well appreciated as participants rated them highly on a visual analogue scale (83 %).

The present data show that there are no significant differences for energy and macronutrient intakes over the course of the ILS, OLS and all six sessions. In fact, this suggests that there is no more variation within each environment than there is between them. In addition, when investigating the present data with regard to sex, while significant differences were noted between men and women, where men consumed a larger quantity of food, no interactions, except for protein intake, were noted between sex and each experimental session. Even though a significant interaction was noted between sex and sessions for protein intake only, no significant differences were observed in protein intake over time when analysing men and women separately. This suggests that within the variations shown for this measurement, this tool can be used in men or women as well as within and outside the laboratory setting. When looking at the distribution of EI, even though no significant differences were noted in main meal and snack intakes, significant differences were indeed noted in energy beverage and water intakes across the sessions. Water intake was higher during the last session of the ILS in comparison with the last session of the OLS, while energy beverage intake was higher during the second and third OLS in comparison with the last session of the ILS. Based on these results, it may be assumed that when participants consumed more water, energy beverage intake was decreased and vice versa. Certain studies⁽Reference Flood, Roe and Rolls^12, Reference DellaValle, Roe and Rolls¹³⁾ have noted an increase in total EI when participants consumed more energy from energy beverages. However, the increases in energy beverage intakes during sessions 2 and 3 of the OLS, in comparison with session 3 of the ILS, in the present study did significantly influence total EI values. Finally, it can be hypothesised that a decrease in water intake may be related to an increase in the intake of water contained in foods. This was, however, not analysed because the quantity of water contained in each food was not available from the software that we used.

The present results also demonstrated positive and significant ICC for total EI during the ILS, the OLS and for the six sessions. The ICC values obtained in the present study are lower than the ICC of 0·97 obtained by Arvaniti et al. ⁽Reference Arvaniti, Richard and Tremblay¹⁾ but are similar to the ICC of 0·86 presented by Gregersen et al. ⁽Reference Gregersen, Flint and Bitz²⁾. It could be argued that the buffet-style meal used by Arvaniti et al. ⁽Reference Arvaniti, Richard and Tremblay¹⁾ was only presented to the participants on one single occasion and this buffet, even if it does provide a wide variety of foods, does not offer any hot food items. Along these lines, Gregersen et al. ⁽Reference Gregersen, Flint and Bitz²⁾ provided a mixed hot-pot meal but, in this case, the EI was only considered for one meal on two separate occasions. A novel aspect of the present study is that nine hot meal-type options were made available from the food menu (Appendix 1) along with most of the items provided in the Arvaniti et al. ⁽Reference Arvaniti, Richard and Tremblay¹⁾ buffet. In addition, our food menu was investigated over several episodes (breakfast, mid-morning and lunch) of feeding as opposed to a single-sitting measure of EI. While we believe that the food menu that was investigated in the present study provides distinctive benefits, we must concede that it is not as reproducible and sensitive as single-sitting measures of EI.

With regard to the CVws values noted in the present study, these are slightly lower than the CVws of 23 % noted by Bingham et al. ⁽Reference Bingham, Gill and Welch¹⁴⁾, obtained with weighed food records over 4 d on four different occasions (total of 16 d). Studies using direct measurements with single-meal designs have reported CVws between about 6 and 10 %⁽Reference Arvaniti, Richard and Tremblay^1–Reference Silverstone, Fincham and Brydon³⁾. These differences are probably explained by the use of single-meal designs, a lower number of food items offered, and possibly because food intake was measured in the laboratory. Although many studies have measured appetitive and food intake responses to manipulations such as knowledge-based work⁽Reference Chaput, Drapeau and Poirier^15, Reference Chaput and Tremblay¹⁶⁾, exercise⁽Reference Pomerleau, Imbeault and Parker¹⁷⁾ and functional foods⁽Reference Yoshioka, Doucet and Drapeau^18, Reference Major, Alarie and Dore¹⁹⁾ with single-meal designs, it should be noted that compensation to dietary⁽Reference Hubert, King and Blundell^20, Reference King²¹⁾ and exercise⁽Reference Stubbs, Sepp and Hughes^22–Reference Whybrow, Hughes and Ritz²⁴⁾ manipulations is often delayed⁽Reference King²¹⁾. As such, the validation of a tool that measures food and beverage intake over multiple meals including snacks may provide a more accurate image of the true effect of such manipulations on EI. It is nevertheless important to note that the measurement of energy and macronutrient intakes over the course of multiple meals and multiple days instead of two meals, as in the present study, would have probably been even more revealing. It would thus be ideal to test this food menu for a more prolonged period to determine whether its reliability would increase under such conditions. In considering such a study, it would be important to weigh the logistical aspects of administration and the cost against the added precision of this tool.

Although some studies have provided foods to participants for consumption outside of the laboratory setting⁽Reference Westerterp, Verboeket-van de Venne and Bouten^25–Reference van het Hof, Weststrate and van den Berg²⁸⁾, to our knowledge, none has tried to study the reproducibility of these tools for measurements of total EI and all macronutrient intakes under free-living conditions. Moreover, the investigation of the same tool both inside and outside of a laboratory setting has never been done before, and the results in the present study indicate that the environment in which the participants consumed the foods and beverages provided to them did not greatly affect their total energy and macronutrient intakes. As such, the reproducibility of our food menu outside and inside of the laboratory setting provides convenience and ecological validity to our tool. However, this tool is accompanied by limitations when used outside of the laboratory, including the fact that it does not offer the certainty that only the foods that were provided were eaten, as is the case when it is used in the laboratory. Although not performed in the present study, adding a follow-up questionnaire to verify whether only foods from the lunch boxes were consumed could help control for this possibility. Additionally, the activities performed by the participants during the OLS were not assessed or restricted. As such, adding an objective measure of participants' physical activity participation outside of the laboratory during the measure of food intake could also help to better understand some of the observed differences.

Furthermore, although the reproducibility of carbohydrate and protein intakes from our food menu was relatively good, it was much less the case for dietary fat. As such, certain studies have found higher variation ratios for fat intake, in comparison with carbohydrate and protein intakes⁽Reference Beaton, Milner and McGuire^29–Reference Ogawa, Tsubono and Nishino³²⁾ when measured over time. Cai et al. ⁽Reference Cai, Shu and Hebert³³⁾ even noted a CVws of 65·3 % in fat intake (g/d) when evaluating data measured over 24 d evenly distributed over 1 year, using 24 h diet recall interviews. This CVws was also higher than the CVws for carbohydrate (29·5 %) and protein (37·5 %) intakes measured over this same time period. When comparing the mean difference in macronutrient intakes using food diaries v. food questionnaires, higher differences were also noted in fat intake (25 %), when compared with protein (5 %) and carbohydrate (4 %) intakes⁽Reference Roddam, Spencer and Banks³⁴⁾. Based on these findings, it may be safe to say that dietary fat intake seems to be more variable than other macronutrients, supporting the idea that dietary fat intake may not be as reproducible over time.

Finally, the present findings are limited to a small normal-weight population, in which case only eight men and eight women were tested. It is thus not surprising to see that the power was low for energy, carbohydrate, dietary fat and protein intakes over several meals. However, as mentioned in the results, the estimate of effect size was also very low for these analyses, indicating that increasing the number of participants would have very likely led to the same results for our primary outcomes. In addition, these results should be interpreted in light of the characteristics of the participants who took part in the present study. Future studies should look into the reproducibility of this tool in populations with different characteristics, such as age and BMI.

Overall, the present results suggest that the food menu investigated in the present study is a reproducible tool that can be used to measure energy and macronutrient intakes under the conditions described in the present study. However, these results also emphasise the difficulties in capturing a stable measure of EI, which is most probably due to the fact that this variable, although relatively stable over long periods of time, presents relatively high day-to-day variations. It is also suggested that both men and women respond similarly with regard to energy and macronutrient intakes, meaning that the reproducibility of this tool is not seemingly affected by the sex of the individual. Future studies should try to find the ideal time frame for the measurement of total EI to obtain stability of the measurement while not making the tool too cumbersome and costly for experimental use.