Total daily energy expenditure has declined over the past three decades due to declining basal expenditure, not reduced activity expenditure

Obesity is caused by a prolonged positive energy balance(1,2). Whether reduced energy expenditure stemming from reduced activity levels contributes is debated(3,4). Here we show that in both sexes, total energy expenditure (TEE) adjusted for body composition and age declined since the late 1980s, while adjusted activity energy expenditure increased over time. We use the International Atomic Energy Agency Doubly Labelled Water database on energy expenditure of adults in the United States and Europe (n = 4,799) to explore patterns in total (TEE: n = 4,799), basal (BEE: n = 1,432) and physical activity energy expenditure (n = 1,432) over time. In males, adjusted BEE decreased significantly, but in females this did not reach significance. A larger dataset of basal metabolic rate (equivalent to BEE) measurements of 9,912 adults across 163 studies spanning 100 years replicates the decline in BEE in both sexes. We conclude that increasing obesity in the United States/Europe has probably not been fuelled by reduced physical activity leading to lowered TEE. We identify here a decline in adjusted BEE as a previously unrecognized factor.

Automated summary

Obesity is caused by prolonged positive energy balance, and the contribution of reduced activity levels to energy expenditure is still debated. Our study shows that total energy expenditure (TEE) adjusted for body composition and age has declined since the late 1980s, while adjusted activity energy expenditure has increased over time in both sexes. The decline in adjusted basal energy expenditure (BEE) is identified as a previously unrecognized factor. These findings suggest that the increasing obesity in the United States/Europe is not likely fueled by reduced physical activity leading to lowered TEE.