[Changes in energy and macronutrient composition among students aged 6-13 in Beijing in 2015 and 2019]

To analyze the changes in energy intake and macronutrient energy contribution among students aged 6-13 years in Beijing, between 2015 and 2019.

A cross-sectional study was conducted in Beijing in 2015 and 2019. Participants were selected using a multi-stage stratified cluster sampling method. Briefly, three urban districts and four suburban districts were chosen. From each district, four primary schools and four middle schools were selected. Within each school, two classes were randomly chosen from grades 1, 3, and 5 of primary schools and grade 1 of middle schools. From one of the two classes in each grade, 12 students were randomly selected for the dietary survey. Valid samples included 1056 students in 2015 and 1125 students in 2019 (aged 6-13 years). Dietary data were collected using the 3-day 24-hour dietary recall method combined with household condiment weighing. Energy intake and energy contribution ratios of carbohydrate, fat, and protein were calculated using the Chinese Food Composition Table. Linear mixed-effects models (LMM) were used to examine changes in continuous outcomes (energy intake and macronutrient energy contribution), while generalized linear mixed-effects models (GLMM) were applied to analyze changes in the risk of abnormal macronutrient contribution (low carbohydrate, high fat). A year-by-district interaction term was included to explore regional heterogeneity, with year 2015 and suburban areas as the reference groups.

No statistically significant differences were observed in the distributions of age and gender between the two survey years. However, the proportion of students from urban areas was significantly higher in 2019 compared to 2015 (χ2= 6.21, P<0.05). In 2015, the energy intake (M(P25, P75)) was 1609.2 (1327.8, 2049.4) kcal/d, with carbohydrate, fat, and protein contributing 49.7%, 35.8%, and 14.5% of total energy, respectively. In 2019, the energy intake decreased to 1492.9 (1225.9, 1803.6) kcal/d, with corresponding percentages of 45.6%, 39.5%, and 14.9%. Significant main effects of year were observed: energy intake and carbohydrate contribution decreased significantly (β= -71.29 and -3.21, P<0.05), while fat and protein contributions increased significantly (β= 2.87 and 0.34, P<0.05). Significant year-by-district interactions indicated that the declines in energy intake and carbohydrate contribution, as well as the rise in fat contribution, were more pronounced in urban than in suburban areas (β=-199.04, -1.75, and 1.62, P<0.05). The proportions of students with low carbohydrate contribution and high fat contribution increased by 20.6 and 11.6 percentage points from 2015 to 2019, respectively, with significantly elevated risks (OR=2.50 and 2.24, P<0.01). The increase in risk of low carbohydrate contribution was significantly greater in urban areas (interaction OR=1.56, P<0.05).

The dietary pattern of students aged 6-13 years in Beijing shifted toward a high-fat, low-carbohydrate profile between 2015 and 2019, with more pronounced changes in urban areas.