Disproportionate declines in physical activity energy expenditure relative to energy intake among Chinese adults: an 18-Year longitudinal study

Obesity is commonly conceptualized as a biological consequence of chronic energy imbalance, in which energy intake exceeds energy expenditure. However, population-level evidence directly evaluating this framework remains limited. This study examined whether the rising prevalence of obesity among Chinese adults reflects long-term changes in energy intake and physical activity (PA)-related energy expenditure. Data were derived from seven waves (2000-2018) of the China Health and Nutrition Survey (CHNS), involving 28 054 adults aged ≥ 18 years. Dietary energy intake was assessed using three consecutive 24-hour (h) recalls, and habitual physical activity was estimated using standardized questionnaires. Longitudinal trends were analyzed using sex-stratified multilevel models. From 2000 to 2018, both dietary energy intake and physical activity-related energy expenditure declined steadily in men and women. The magnitude of decline in energy expenditure attributable to reduced physical activity was substantially larger than that of dietary energy intake, reaching 86.4 kcal/day in men and 65.6 kcal/day in women, compared with intake reductions of 19.3 kcal/day and 15.3 kcal/day, respectively. During the same period, body weight and obesity prevalence increased steadily. Long-term reductions in physical activity-related energy expenditure exceeded declines in dietary energy intake and were closely aligned with rising obesity among Chinese adults. Strategies to promote leisure time physical activity may be critical for restoring energy balance in the context of ongoing urbanization and socioeconomic change.