Changes in body composition, PSC, PSCP, MVPA.

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不断提升，青少年的必需体力活动量逐渐减少，而零食供应愈发充足，进一步引发青少年肥胖问题。本研究为一项纵向两阶段观察性研究，共纳入74名超重与肥胖青少年，以校园环境与家庭环境为两个研究阶段展开。研究在三个时间节点采集数据：学期中期（T0）、学期末（T1）以及寒假结束时（T2）；并采用多元线性回归（multivariate linear regression）与格兰杰因果检验（Granger causality tests）开展分析，探究多阶段中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）、零食蛋白质热量占比（proportion of snack calories from protein, PSCP）]的变化规律，及其变化对身体成分的影响。研究结果显示，在学期阶段，ΔMVPA与ΔPSCP的升高、ΔPSC的降低与Δ体脂百分比（body fat percentage, BFP，Δ=后一时间点数值−前一时间点数值）的下降呈显著相关。而在假期阶段，ΔPSCP、T1时点的MVPA与PSCP的下降，以及ΔPSC的升高，则与ΔBFP的上升呈显著相关。仅MVPA对去脂体重（fat-free mass, FFM）具有正向因果预测效应。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、选择高蛋白零食，对于管控青少年肥胖尤为关键，尤其在假期时段。此外，还应推行提升MVPA的相关策略，以增加去脂体重，进而间接实现肥胖管控目标。