We aimed to estimate the association between changes in NEDF consumption and BMI change in school-age children. Over an average of 6.1 years of follow-up children increased their NEDF consumption by 225 kJ (53.9 kcal), yet, we did not observe an association between NEDF increases and BMI increase (0.033 kg/m2, [p = 0.246]). However, in fully adjusted models BMI increased 0.078 kg/m2 for every 418.6 kJ/day (100 kcal/day) of sweet bakery products intake (p = 0.035). Increases in the consumption of chips and popcorn were associated with a 0.208 kg/m2 increase in BMI in unadjusted models; however, this association was attenuated in fully-adjusted models. Changes in the consumption of other food groups within the NEDF classification did not show an association with changes in BMI.
Few efforts have been made to estimate the association between NEDF consumption and weight in school-aged children. Some cross-sectional studies have described a positive association between NEDF and weight gain [12, 39], however, the few longitudinal studies available have shown mixed results. In two studies, the first under five years of age and the second with a mean age of 16 years, children’s weight tended to decrease with higher levels of consumption of NEDF [19, 20]. A positive association was observed in a study of 961 children 5 to 12 years of age, that defined dietary patterns rich in high-energy and low-nutrient-density foods as exposure [21] with 2.5 years follow-up. Similarly, Phillips, et al, found a non-significative result that children’s weight tend to increase with more joules (calories) from NEDF consumption in a cohort of 166 non-overweight school-aged girls followed for seven years [22], both of these cohort studies used mixed-effect models which can not control for time-invariant confounders as effectively as fixed effects models. Our study is unique in that we are assessing the impact of changes in NEDF consumption and changes in BMI; under this approach we did not detect an association between NEDF and BMI overall, but we did identify a significant association with the consumption of sweet bakery products.
The association between sweet bakery product consumption and weight gain has been reported in two other prospective studies. Phillips et al., in a girls’ cohort study with an average follow-up of seven years, found an increment of z-score in BMI (0.003; p = 0.11), with more intake of cookies, pies, cakes, brownies, chocolate candy, nonchocolate candy, ice cream, milkshakes sherbet, potato chips and corn chips [22]. The non-significant result for potato chips and popcorn un our study could be explained by a lack of power to detect the effect due to a small sample size and the small number of energy-dense foods included in the food frequency questionary. In the preset study we identified more than 90 different types of NEDF in children’s diet. Also, in a prospective cohort study with more than 120 thousand adults followed for 20 years the consumption of one serving of potato chips per day or refined grains (including sweet bakery products) was associated with increment in body weight of 0.77 kg and 0.25 kg in a 4-year period, to each food product, respectively [34]. Negative associations between chips and bakery and BMI have also been reported. Field et al., in a cohort of children and adolescents with three years of follow-up found a reduction of 0.006 in BMI z-score (p < 0.05) among those eating energy-dense foods; however, this association became non-significant after adjusting for dieting status and maternal overweight [23].
In our study we found that eating ready-to-eat cereals was marginally associated with a BMI reduction of -0.098 kg/m2 for every 418.6 kJ/day (100 kcal/day). Consumption of ready-to-eat cereals has been related to a healthy dietary pattern in children [40] and this include more consumption of vitamins and minerals, less of saturated fat and cholesterol, but also, with a higher intake of added sugar [40, 41]. Negative associations between ready-to-eat cereals and BMI, have also been reported in longitudinal analyses [42, 43]. However, ready-to-eat cereals comprises many different products, and their nutritional impact will depend on the composition of the cereal, and the food consumed with them (such as fruit or milk); our study, as well as all previous studies available could be confounded by these characteristics. Even though ready-to-eat cereals may be associated with weight lost in children, children consuming a non-high fiber cereal, had worse type 2 diabetes risk profile than children consuming a high fiber cereal in a longitudinal study [44].
There are three different explanations for the association between sweet bakery products consumption and weight gain. First, sweet bakery products tend to be high in added sugar, saturated fat and of course high quantities of energy in small portions of food [10] and may promote excess energy intake without control over the joules (calories) consumed. In a recent crossover trial, adults were randomized to receive an ultra-processed (generally energy-dense food) or unprocessed diet for a period of 2 weeks. Participants in the ultra-processed diet increased 0.8 kg and those in the unprocessed diet reduced 1.1 kg. Those in the ultra-processed diet consumed 2126 kJ/day (508 kcal/day) more than the other group, mainly by fats and carbohydrates [45]. Second, many sweet bakery products are high in refined carbohydrates and starches and may induce stronger insulin secretion. This promotes less satiating signals, increasing subsequent hunger feelings [46] and suppresses the release of fatty acids from adipose tissue into circulation, while keeping glucose and fatty acids away from the oxidation process to store them in the adipose tissue [47]. Third, a diet rich in energy-dense food is associated with less protein consumption in children and according with the “protein leverage hypothesis” this may be related to the disturbance of the appetite system through increased postprandial hunger and reduced postprandial satiety [48].
Strengths of this study include the prospective cohort design, including three measurements of anthropometric and dietary information, large sample size and the approach analysis with the possibility to assess the change in change effect. Our study also has some important limitations that must be taken into account to interpret our results. First, at each wave we had one dietary evaluation, instead of two or more 24-hour recalls, which may not reflect usual NEDF consumption. Second, we lost 14.1% of the sample in the first period and 29.3% in the second; however, baseline socioeconomic index, children sex at baseline, age and maternal education, and overweight status were no different between children lost and those who stayed in the cohort.
In summary, our results showed that consumption of NEDF overall was not associated with BMI in children. However, NEDF subgroups such as sweet bakery products and, possibly, chips and popcorn, showed an association with BMI. The longer-term effect of NEDF consumption in school-aged children on BMI requires further studies with bigger samples, better follow-up, and the use of an objective measure of adipose tissue in order to obtain more reliable results. Decreasing the consumption of NEDF is a key step to improve dietary quality and prevent obesity, aligned with the WHO 25x25 goals [49] and the Sustainable Development Goals [50]. In Mexico, a strategy to reduce NEDF consumption is in place, limiting access to these foods in elementary schools [51], restricting food marketing to children on television and public areas [52], and implementing an 8% tax to all NEDF [31]. However, further public health efforts need to be directed to reduce the consumption of NEDF, particularly early on in life.