Descriptive statistics.

With rising incomes in developing countries, the required necessary physical activity declines and the availability of snacks increases, further causing obesity in adolescents. The study was a longitudinal two-stage observational study of 74 overweight and obesity adolescents distinguishing between school and home environment phases. Data were collected at three time points (mid-semester (T0), end of semester (T1), and end of the winter holidays (T2)), and explorations were conducted using multivariate linear regression and Granger causality tests to investigate how changes in moderate-to-vigorous physical activity(MVPA), snacking habits (proportion of snack calorie, PSC; proportion of snack calories from protein, PSCP) in multiple stages and how their changes affect body composition. The results showed that during the semester phase, increases in ΔMVPA and ΔPSCP and decreases in ΔPSC were associated with decreases in ΔBFP (Δ = post-timepoint value − pre-timepoint value). During the holiday phase, decreases in ΔPSCP, MVPA (T1), and PSCP (T1), and increases in ΔPSC were associated with increases in ΔBFP. Only MVPA having a positive predictive effect causally on FFM. Snacking habits have a significant impact on body composition changes in adolescents, and reducing snack intake and choosing high-protein snacks are critical to controlling obesity in adolescents, especially during the holiday period. Strategies to increase MVPA should also be implemented to increase FFM briefly indirectly control obesity.

随着发展中国家居民收入水平提升，青少年日常所需体力活动量下降，同时零食可及性不断提高，进而进一步加剧青少年肥胖问题。本研究为一项纵向两阶段观察性研究，共纳入74名超重及肥胖青少年，研究周期划分为校园环境与家庭环境两个阶段。研究在三个时间节点采集数据：学期中（T0）、学期末（T1）以及寒假结束时（T2）；并采用多元线性回归与格兰杰因果检验开展分析，探究多阶段内中等至高强度体力活动（moderate-to-vigorous physical activity, MVPA）、零食摄入习惯[零食热量占比（proportion of snack calorie, PSC）、蛋白质来源零食热量占比（proportion of snack calories from protein, PSCP）]的变化及其对身体成分的影响。研究结果显示，在学期阶段，ΔMVPA与ΔPSCP的提升、ΔPSC的降低与体脂百分比变化量（ΔBFP，Δ=后时间点值-前时间点值）的下降呈显著关联；而在假期阶段，ΔPSCP的降低、T1节点的MVPA与PSCP水平下降，以及ΔPSC的提升则与ΔBFP的升高呈显著关联。仅MVPA对瘦体重（fat-free mass, FFM）具有因果层面的正向预测作用。零食摄入习惯对青少年身体成分变化具有显著影响，减少零食摄入量并选择高蛋白零食对于防控青少年肥胖至关重要，尤其在假期阶段。此外，还应实施提升MVPA的相关策略，以增加瘦体重，进而间接实现肥胖防控目标。