Overview

• The PNAS study used doubly labeled water measurements from more than 4,200 adults across 34 global populations to directly assess energy expenditure and body composition.
• After adjusting for body size, total and basal metabolic rates fell modestly with economic development while activity-related energy use remained unchanged.
• Higher intake of ultraprocessed foods explained roughly nine-tenths of the increase in obesity linked to economic development, with metabolic shifts accounting for the remaining one-tenth.
• Obesity prevalence was greatest in middle- and high-HDI countries—particularly among women—and greater fat-free mass in these populations causes BMI to overestimate true adiposity.
• Authors stress next steps to identify the specific ultraprocessed ingredients behind rising calorie intake and to prioritize policies on food quality, access and regulation alongside physical activity promotion.