New Study Questioning Exercise’s Role in Weight Loss

It might sound counterintuitive, but a recent study suggests that exercising may not play as significant a role in weight loss as we’ve been led to believe. For years, the common wisdom has been simple: to burn off extra calories, just move more. Indulged in a treat? No biggie—just hit the gym to compensate.

However, this new research, which analyzed data from over 4,200 individuals in 34 countries, casts doubt on that idea. It turns out, people who engage in more physical activity don’t necessarily burn significantly more calories than those who are more sedentary. Interestingly, the study points out that a hunter-gatherer from Tanzania’s Hadza community expends about the same number of calories each day as a typical American office worker, despite the Hadza’s more active lifestyle.

There were minor variations in calorie burn among individuals, but they were quite negligible. Only about 10 percent of the calorie differences could be attributed to exercise itself.

“We used to believe that increased physical activity directly impacted daily calorie burn. But over the last decade, it’s become clear that the relationship isn’t that straightforward,” explains Duke University’s Prof Herman Pontzer, one of the lead researchers behind this study.

So, does this mean we should toss our sneakers and cancel our gym memberships? Not exactly. While it appears that the amount we exercise has little effect on our weight, totally abandoning physical activity isn’t the solution either.

Understanding Metabolism

If, as this new study indicates, exercise accounts for only a small part of daily calorie expenditure, then what else is using up our energy? The answer lies in all the bodily processes that keep us alive—everything from respiratory function to digestion, immune response, and cognitive processes—they all require a significant amount of energy. This baseline energy requirement, often referred to as basal metabolic rate (BMR), forms the bulk of our daily calorie burn.

Here’s the catch: individuals with more body mass tend to have a higher BMR. Surprisingly, an overweight American office worker often has a higher daily calorie expenditure than a Hadza hunter-gatherer simply due to their size.

“People in developed nations generally burn more calories daily compared to those in traditional societies. This is primarily because they tend to be larger, and larger individuals burn more,” Pontzer notes. When you adjust for body size and composition, the differences in energy use among global populations become minimal.

The Calorie Equation

So, how is it possible that people of different activity levels burn roughly the same calories for their size? Pontzer explains that our metabolism adjusts to our activity levels. Essentially, when we increase or decrease our physical activity, our bodies compensate by conserving energy in other areas.

This balancing act, known as homeostasis, means that if you suddenly ramp up your morning workouts, your body will conserve energy from other necessary functions to accommodate that increase in activity.

“Our bodies adapt to our lifestyles,” Pontzer elaborates. “If you’re more active, your body shifts energy use away from other processes to maintain overall calorie expenditure.”

While this might seem concerning at first, Pontzer argues that managing calorie expenditure in this way can be beneficial. Redirecting energy can help reduce inflammation and contribute to better overall health.

That said, pushing your limits too hard can lead to negative outcomes, like overtraining syndrome, which may cause various health issues. This usually isn’t a problem for most people outside professional athletics.

The reverse also applies: if someone suddenly stops exercising, their metabolism will adjust, redirecting energy back to functions like inflammation.

Diet as the Main Factor

In short, Pontzer stresses that the real factor linked to body fat isn’t exercise but diet. “The weight we carry reflects the calories we consume and don’t burn off,” he explains. If energy expenditure doesn’t vary substantially, it naturally points to dietary habits being the primary driver of weight gain.

This study highlights that ultra-processed foods—those factory-made products like snacks, sweets, and convenience meals—are a significant factor in rising obesity rates, rather than just the amount of proteins or other food groups consumed.

“What we observed is that across various groups, the quantity of ultra-processed foods correlates strongly with body fat percentages,” Pontzer adds.

While these findings are compelling, they come with caveats. The researchers didn’t track specific diets or individual food intake; instead, they used broader data from national surveys to assess typical diets. This limitation is crucial since we can’t directly link food intake, body fat, and energy use on an individual level, raising questions about the underlying reasons for the observed obesity trends.

It could be the case that ultra-processed foods have a particularly detrimental effect or that they facilitate overeating because of their enticing taste and energy density.

“It’s not necessarily the processing itself,” argues Dr. Adam Collins, a nutrition professor, “but rather the hyper-palatable features and energy density of these foods that lead to higher consumption.”

Ultra-processed foods are designed to be delicious, often high in fat, sugar, and salt while lacking in fiber and essential nutrients, making it easy to overeat them.

“When people try cutting ultra-processed foods, they usually eat less and become more aware of their food choices, often leading to weight loss and better health,” Collins points out.

He doesn’t suggest that all ultra-processed foods should be eliminated. Instead, he advocates for a more mindful and moderated approach to consuming them.

Exercise’s Continued Importance

This study isn’t without its critics; Collins is one of them, noting that exercise still plays an important role in weight maintenance. “While it may not be as effective for burning calories directly, exercise helps regulate appetite and influences body composition by reducing fat and increasing muscle,” he argues.

Since muscle cells require more energy than fat cells, increasing muscle mass can slightly elevate daily caloric needs. Yet, Pontzer acknowledges this can lead to small, marginal changes, suggesting most weight loss programs don’t rely on these effects.

Collins holds a different view, calling for extended research to validate or refute Pontzer’s findings over a longer term.

Conclusion

Despite differing opinions on exercise’s effectiveness for weight loss, everyone agrees on its numerous benefits: strengthening the heart, protecting bones, supporting metabolic health, and enhancing mental wellbeing—all contributing to a longer, healthier life.

Pontzer hopes this research will shift how we approach weight management, particularly focusing on diet. However, he emphasizes that exercise should remain a part of a healthy lifestyle.

“We shouldn’t equalize the blame between diet and exercise for obesity; diet clearly seems to be a stronger factor,” he concludes. “This doesn’t mean we should stop encouraging physical activity, as it is still essential for overall health.”