It’s a logical yet concrete idea: the more you move, the more calories you burn, and the more weight you lose. However, this is not always the case for many people.
In controlled studies, physical activity often results in less weight loss than predicted by caloric models. Even by adding aerobic exercises like walking, running, and cycling, most participants only lose an average of 1.3 kg over six months. These are mixed results for a significant investment in time and effort, which have puzzled researchers for a long time.
You may already know part of the explanation: exercising increases appetite, making it easier to absorb the lost calories. But specialists are also trying to understand another phenomenon at play, which defies all logic.
In an analysis published in 2025, it was shown that participants only burned about one-third of the additional calories theoretically required by their physical activity. In other words, a jog that should have burned 500 calories only added around 165 calories to daily caloric needs. Therefore, the body compensates for increased physical activity by reducing energy expenditure elsewhere. The extent and manner in which it does so remain a mystery, as noted by Vincent Careau, an evolutionary biologist at the University of Ottawa, Canada.
This emerging idea, known as “energy compensation,” challenges a long-standing hypothesis at the core of fitness culture, which posits exercise as a weight loss driver. Instead, researchers suggest it may be more effective in helping the body maintain its weight and stay healthy in the long run.
The concept of compensation emerged after a groundbreaking study in 2012 showing that hunter-gatherers in Tanzania burned roughly the same number of calories as sedentary individuals in industrialized countries, despite covering much greater daily distances for food hunting.
This counterintuitive discovery is explained by the limited energy expenditure model, where the body compensates for physical activity by reducing energy consumed by other physiological processes. Thus, our total daily energy expenditure (which includes blood pumping, digestion, movement, and voluntary physical activity) remains mostly unchanged.
This adjustment can take various forms, as explained by Leanne Redman, a specialist in human physiology and energy balance at the University of Sydney. In a study she authored in 2021, adults burning around 1,800 calories per week through sports only lost about half the expected weight as per caloric models.
Changes in movements could partly explain this difference, although it was not confirmed by the study’s findings. People engaging in physical activity might nap on the couch due to fatigue, walk slower to the bus stop, or even take an Uber, leading to less energy expenditure.
However, not everyone compensates in the same way. Follow-up analyses found that only half of the participants showed clear signs of compensation, mainly when exercise became less challenging for them.
While some scientists doubt the reality of compensation, recent studies have shown an exponential increase in total energy expenditure with physical activity among sedentary volunteers and ultra-marathon runners. Surprisingly, no compensation related to changes in behavior or a slowdown in immune or thyroid function was observed in both groups.
This aligns with previous work showing that more physical activity generally leads to higher calories burned, especially among those with a negative energy balance. Nevertheless, individuals in energy balance or surplus showed no compensation, indicating that the phenomenon may occur when calories are scarce.
Many specialists believe the truth lies somewhere between the two models and urge caution in drawing hasty conclusions. Even if exercise does not always result in significant weight loss, it can contribute to maintaining weight loss by improving insulin sensitivity and offering various health benefits like reduced cholesterol, inflammation, and disease risk in old age.
Ultimately, as Kristen Howard concludes, anyone studying the matter would want to highlight the incredible benefits of sports and physical activity.
