(PTFS14-03-24) Longitudinal Changes in Adherence to US Dietary Guidelines and Associations With Body Mass Index Among Adolescents in the Growing Up Today Study: A Change-in-Change Study

Objectives: While the Dietary Guidelines for Americans (DGAs) form the nutritional basis for food assistance programs for youth, few studies have examined longitudinal relationships between adherence, via the Healthy Eating Index (HEI), and BMI in adolescents. We leveraged 7 years of data from the Growing Up Today Study (GUTS) to evaluate within-child associations between changes in overall and component HEI scores and changes in BMI in US school-aged children.

Methods: We analyzed prospective data from GUTS; a longitudinal cohort with two enrollment cycles in 1996 (n=15,667 at baseline) and 2004 (n=10,553). We calculated HEI-2020 and BMI changes between survey cycles using a validated food frequency questionnaire and self-reported height/weight. Generalized estimating equation models, stratified by natal sex, were used to estimate associations between concurrent HEI and BMI change, accounting for clustered data and covariates. We assessed interaction by concurrent overweight and obesity status at the start of each period.

Results: Participants were 9-17 years at baseline, on average at the 56th BMI percentile, with an average HEI of 58.9 points (pts). After covariate adjustment, a 10pt increase in overall HEI was associated with 0.10 kg/m² (95%CI: 0.06, 0.15) decrease in BMI for boys alone, with no overall association seen for girls. For HEI component sub-scores, increases in the greens & beans and fatty acid scores were associated with reductions in BMI for both boys and girls, while an increased seafood/plant protein score was associated with reduced BMI for boys alone. Meanwhile, among girls, a 1pt increase in dairy score was associated with 0.03 kg/m² (0.01, 0.04) BMI increase. For boys, associations between HEI and BMI change were largest for those classified with obesity, for whom a 10pt increase in overall HEI was associated with a 0.34 kg/m² (0.06, 0.61) BMI decrease.

Conclusions: Improved adherence to dietary guidelines overall was associated with BMI decline for boys, but not girls, and relationships were strongest for boys with obesity. Alternative diet quality indices based more closely on dietary risk factors for excess weight gain may be better predictors of BMI in youth. Future research should continue to examine relationships between DGA adherence and the broad range of outcomes for which they were designed.

Funding Sources: NHLBI