A global analysis of 4,213 adults from 34 populations across six continents found that total energy expenditure was not the primary factor behind higher obesity rates in more economically developed countries.
Populations studied ranged from hunter-gatherers and pastoralists to residents of industrialized nations, with total energy expenditure (TEE), basal energy expenditure (BEE), activity energy expenditure (AEE), and body composition measured using the doubly labeled water method and isotope dilution.
Obesity prevalence, defined as body mass index (BMI) ≥ 30 kg/m², was significantly higher in middle- and high-income countries compared with less-developed populations. More developed groups also had greater body mass, BMI, and body fat percentage. While absolute TEE was higher in developed countries, this was largely due to greater body size and fat-free mass rather than higher physical activity.
After adjusting for body size, differences in TEE across economic levels were small—about 6% lower from the least to most developed groups. AEE and physical activity level (PAL) showed no significant differences between low- and high-income populations after accounting for body size, sex, and age. Traditional populations in some cases had size-adjusted TEEs similar to or greater than those in industrialized countries.
The association between TEE and obesity measures was weak. Among men, higher TEE adjusted for fat-free mass was linked to slightly lower body fat percentage, but the effect was small. In women, there was no significant relationship between TEE and body fat percentage. Variations in TEE explained only about one-tenth of the increased BMI and body fat percentage associated with economic development.
Dietary patterns, particularly the proportion of ultraprocessed foods (UPF), were more strongly associated with body fat percentage. In the 25 populations with dietary data, higher UPF intake was linked to greater body fat percentage, even after controlling for age, sex, TEE, and economic status. Per capita meat consumption was not significantly associated with adiposity when UPF percentage was considered.
These findings indicate that increased caloric intake, especially from UPF, plays a more substantial role than reduced energy expenditure in the rise of obesity with economic development. While physical activity remains important for overall health, obesity prevention strategies may benefit from greater focus on dietary factors.
Study limitations included its cross-sectional design, which prevents establishing causality, and the absence of detailed dietary nutrient data for many populations. The authors also noted that the environmental, societal, and physiological factors influencing increased caloric intake and absorption in more developed settings were not fully identified. The 7- to 14-day measurement period for energy expenditure may not reflect long-term patterns.
The study concludes that differences in total energy expenditure are small and inconsistent in explaining global disparities in obesity, whereas dietary patterns—particularly ultraprocessed food consumption—are more closely aligned with obesity prevalence across economies.
The authors reported no conflicts of interest.
Source: PNAS
