A new analysis reveals that the body compensates for increased exercise by reducing energy use elsewhere, limiting weight loss. This effect is stronger when combined with dieting. Researchers from Duke University examined 14 trials to reach these findings.
Exercise improves health in numerous ways but falls short for shedding pounds, according to a detailed review published in Current Biology. Herman Pontzer and Eric Trexler at Duke University analyzed data from 14 trials involving about 450 participants. They found that total energy expenditure rises by only about a third of the expected amount when people ramp up physical activity.
For example, if someone burns an extra 200 kilocalories through exercise, their overall daily energy use might increase by just 60 kilocalories. This compensation—where the body cuts energy for background functions like resting metabolism—explains why weight loss is less than anticipated. Pontzer notes that this pattern emerged from his earlier work with Hadza hunter-gatherers in Tanzania, who maintain high activity levels yet expend no more energy than sedentary office workers. He first proposed in 2015 that human physiology evolved to cap total energy burn.
The compensation intensifies when exercise pairs with calorie restriction. "The real killer here is that if you pair exercise with diet, your body goes, ‘fine, well, then I’m going to compensate more’,” Pontzer says. In such cases, total energy expenditure often stays flat despite added workouts.
Exercise type influences outcomes. Aerobic activities like running trigger compensation, while resistance training such as weightlifting boosts energy use beyond expectations—rising 250 kilocalories for a 200-kilocalorie input. However, weightlifters in the studies gained muscle but lost little fat, so it remains ineffective for weight reduction.
Pontzer suggests the body adjusts organ functions post-exercise, potentially lowering resting metabolic rate during sleep. "We’re changing what our different organ systems are doing [after exercising],” he explains.
Not all experts agree. Dylan Thompson and Javier Gonzalez at the University of Bath question the results, citing a meta-analysis showing no change in resting metabolism from aerobic exercise. Gonzalez adds that added workouts might simply replace daily tasks like gardening. Pontzer counters that some studies rule out such substitutions, and animal research supports the compensation effect. Both skeptics call for more rigorous randomized trials.
