Obesity is the cause of more than 4 million deaths and leaves millions more people disabled worldwide each year. It is now becoming more common also in the developing countries, as body fat increases in parity with economic development. Usually experts explains obesity as caused by less physical activity and a changed diet towards one with a larger calory intake. A recent study, “Energy expenditure and obesity across the economic spectrum”, published in the Proceedings of the National Academy of Sciences (PNAS), examines the role of physical activity in the global obesity epidemic, using data from diverse populations to test whether reduced energy expenditure due to sedentary lifestyles is the primary driver of rising obesity rates.
Methodology
The researchers analyzed data from over 4,200 adults across 34 communities worldwide, with very different life-styles, spanning from traditional hunter-gatherer societies in Africa to urban residents in wealthy industrialized nations. They employed the precise “doubly labeled water” technique – a gold-standard method involving traceable isotopes – to measure total daily energy expenditure and body composition. This data was drawn from the International Atomic Energy Agency’s global energy expenditure database, allowing for a comprehensive cross-cultural comparison.
Diet Is All That Matters
Contrary to common belief, individuals in wealthier, more industrialized countries actually expend more total energy per day than those in traditional societies. A sedentary office worker can burn almost as much energy in a day as a physically active person, due to factors like higher basal metabolic rates and non-exercise activities (e.g., fidgeting or occupational demands).
Despite this increased energy output, obesity rates are higher in developed nations because calorie intake rises even more dramatically, leading to excess body fat accumulation.
In populations with available dietary data, consumption of ultra-processed foods was strongly correlated with higher body fat percentages, underscoring diet’s outsized influence on BMI and fat mass.
Conclusions
The result of the study challenges the common belief that simply increasing physical activity can effectively combat obesity. It concludes that diet, not a lack of physical activity, is the dominant factor in the obesity epidemic. Even how much is eaten has less significance to what is eaten as the ultra-processed foods are the ultimate driver of the obesity epidemic.
Exercise still remains crucial for health but it does not effectively counteract the caloric surplus from modern diets. The authors advocate for policy interventions focused on regulating food environments to curb access to calorie-dense, ultra-processed foods. This research shifts the emphasis from “move more” campaigns to dietary reforms as the key to addressing obesity.
