Data from: The statistical mechanics of human weight change

Over the past 35 years there has been a near doubling in the worldwide prevalence of obesity. Body Mass Index (BMI) distributions in high-income societies have increasingly shifted rightwards, corresponding to increases in average BMI that are due to well-studied changes in the socioeconomic environment. However, in addition to this shift, BMI distributions have also shown marked changes in their particular shape over time, exhibiting an ongoing right-skewed broadening that is not well understood. Here, we compile and analyze the largest data set so far of year-over-year BMI changes. The data confirm that, on average, heavy individuals become lighter while light individuals become heavier year-over-year, and also show that year-over-year BMI evolution is characterized by fluctuations with a magnitude that is linearly proportional to BMI. We find that the distribution of human BMIs is intrinsically dynamic—due to the short-term variability of human weight—and its shape is determined by a balance between deterministic drift towards a natural set point and diffusion resulting from random fluctuations in, e.g., diet and physical activity. We formulate a stochastic mathematical model for BMI dynamics, deriving a theoretical shape for the BMI distribution and offering a mechanism that may explain the right-skewed broadening of BMI distributions over time. An extension of the base model investigates the hypothesis that peer-to-peer social influence plays a role in BMI dynamics. While including this effect improves the fit with the data, indicating that correlations in the behavior of individuals with similar BMI may be important for BMI dynamics, testing social transmission against other plausible unmodeled effects and interpretations remains the subject of future work. Implications of our findings on the dynamics of BMI distributions for public health interventions are discussed.过去35年间，全球肥胖患病率几乎翻倍。体质量指数（Body Mass Index，BMI）分布在高收入社会中持续向右偏移，这与平均BMI的升高相对应，而平均BMI的升高源于已被充分研究的社会经济环境变化。然而，除了这种整体偏移之外，BMI分布的具体形态随时间也发生了显著变化，呈现出持续的右偏展宽现象，其背后机制尚未得到充分阐释。本研究整合并分析了迄今为止规模最大的年度BMI变化数据集。该数据集证实，平均而言，体重超标者的体重会逐年降低，而体重偏轻者的体重则逐年升高；同时还表明，年度BMI变化的特征是波动幅度与BMI呈线性正比关系。我们发现，由于人体体重存在短期波动，人类BMI分布本质上是动态的；其形态由朝向自然设定点的确定性漂移，与饮食、体力活动等随机波动引发的扩散效应之间的平衡所决定。我们构建了BMI动态变化的随机数学模型，推导出BMI分布的理论形态，并提出了一种可解释BMI分布随时间发生右偏展宽的机制。本研究对基础模型进行扩展，验证了"同辈间社会影响对BMI动态变化具有作用"这一假说。尽管加入该效应后模型与数据的拟合度有所提升，提示BMI相近个体的行为相关性可能对BMI动态变化具有重要意义，但相较于其他未被建模的合理效应与解释，对社会传播效应的验证仍有待未来研究开展。本研究还探讨了我们关于BMI分布动态变化的发现对公共卫生干预的启示。