The long-held belief that exercise guarantees weight loss is being challenged by new research suggesting the body actively compensates for calories burned during physical activity. A study published in Current Biology indicates that the increase in total energy expenditure following exercise may be significantly less than previously estimated, raising questions about the effectiveness of exercise as a standalone weight loss strategy.
Researchers at Duke University, Herman Pontzer and Eric T. Trexler, analyzed data from 14 clinical trials involving 450 participants. Their findings suggest that, on average, only 30% of the calories burned through exercise result in a net increase in total daily energy expenditure. The remaining 70% is offset by the body reducing energy use in other areas, such as cellular repair processes. This supports the “constrained” model of energy expenditure, which posits that the body strives to maintain a stable energy balance.
“If you burn 200 kilocalories doing exercise, you don’t actually see your total energy expenditure go up by 200 kilocalories,” explained Pontzer to New Scientist. “It only goes up by about 60 kilocalories.”
The study also revealed a surprising nuance: the body’s compensatory response appears to be more pronounced when exercise is combined with dieting. Individuals who reduced their caloric intake while exercising experienced even less of an increase in total energy expenditure. Pontzer suggests that the body interprets simultaneous calorie restriction and exercise as a signal to further conserve energy.
However, the type of exercise also appears to play a crucial role. While aerobic exercise – such as running, swimming, and cycling – triggered a significant compensatory response, resistance training, like weightlifting, yielded different results. The analysis indicated that energy expenditure increased more closely to the amount of calories burned during resistance exercise. For example, burning 200 kilocalories through weightlifting led to an increase of approximately 250 kilocalories in total daily energy expenditure, potentially due to the energy required for muscle repair and growth.
Despite the increased energy expenditure with resistance training, the researchers noted that participants did not necessarily lose fat, but rather gained muscle mass. This suggests that while resistance training may be beneficial for body composition, it isn’t automatically a pathway to weight loss.
Experts caution that these findings should be interpreted with nuance. The study acknowledges the possibility that the exercise undertaken by participants may have displaced other forms of physical activity they would have otherwise engaged in. Further research is needed to fully understand the complex interplay between exercise, metabolism, and weight loss.
The findings reinforce the importance of a holistic approach to weight management, emphasizing the central role of diet. As one expert noted, “Alimentation adaptée reste la clé dans la régulation du poids” (adapted nutrition remains the key to weight regulation), according to Pourquoidocteur.fr.