Assessing the longitudinal association between sleep, diet quality and BMI z-score among Black adolescent girls

Background: Cross-sectional research has suggested associations between diet, sleep and obesity, with sparse longitudinal research. Objectives: To identify longitudinal mechanistic associations between sleep, diet and obesity. Methods: We used longitudinal data from a sample of Black adolescent girls. At T1 (enrolment), 6 months (T2) and 18 months (T3), we estimated sleep duration and quality (7-day accelerometry), diet quality (Healthy Eating Index [HEI-2020]) and body mass z-scores (zBMI) from measured height and weight. Longitudinal mediation using structural equation models examined the mechanistic roles of sleep, diet quality and zBMI. Results: At enrolment, girls (n = 441) were mean age 12.2 years (±0.71), 48.3% had overweight/obesity, and mean HEI 55.8 (±7.49). The association between sleep and diet quality did not vary over time. Sleep duration at T1 was not associated with diet quality at T2 nor was diet associated with zBMI at T3. The bootstrapped indirect effect was not significant. Sleep quality at T1 was not associated with diet quality at T2 nor was diet associated with zBMI at T3. The bootstrapped indirect effect was not significant. Conclusions: Diet was not a mediator between sleep and obesity. Study strengths are the longitudinal design and direct measures of sleep and zBMI among a homogeneous sample.