A nutritionist says exercise doesn't help you lose weight. "All the studies prove it."

" Exercise doesn't help you lose weight . All the studies show that." That's how Tim Spector , a professor at King's College London and one of the world's leading nutrition experts, asserted. He stirred up the debate about weight and healthy habits in a recent interview. The doctor stated that "it has been greatly exaggerated as an easy solution to obesity ."

Spector bases his position on decades of scientific research showing that exercise alone doesn't lead to significant weight loss. He explains that it can serve as a support for maintaining weight once achieved through dietary changes , but not as a primary weight-loss strategy. "If you don't change your diet, exercise is useless for weight loss. And all the experts already know that," he stated.

The reason lies in the human body's evolutionary mechanisms , which tend to compensate for energy expenditure after physical activity. "We exercise and then our metabolism slows down ; the body tries to recover the lost energy, and it also tends to make us hungrier," he noted. Consequently, according to Spector, not only is it not an effective way to lose weight, but it can have the opposite effect if not accompanied by a proper diet.

Those interested in the hoax

For Spector, there are clear economic interests behind this misconception. "For 30 years, far more research has been funded on the relationship between exercise and weight than on sugar and weight," he charged. According to him, large beverage and ultra-processed food corporations have funded studies that reinforce the belief that a sedentary lifestyle is the primary cause of obesity. This has allowed them to continue selling high-calorie products while shifting the solution to sports. "That's why Pepsi and Coca-Cola have sponsored sporting events for years. They sell us the idea that childhood obesity is the fault of not having enough parks, not soda," he criticized.

Even "sugar-free" soft drinks aren't safe. The epidemiologist noted that in studies conducted with children and adolescents who replace sugary soft drinks with "zero" versions, no differences in weight or metabolism were found. "It's true that they have fewer cavities , but the rest of the benefits are not evident," he asserted. The reason? According to Spector, sweeteners negatively affect the intestinal microbiota and alter flavor perception , stimulating a preference for sweetness even without calories. "Even the most 'natural' ones, like stevia, are not harmless. They alter the intestinal flora and cause spikes in blood sugar ," he warned.

The energy balance

Spector also questions another of the great mantras of modern nutrition: the "calories in vs. calories out" equation. "Big brands need us to believe that all calories are equal ," she said. But, in her opinion, this approach is flawed and reductionist. "That way, they can sell us the idea that as long as we don't exceed a certain number of calories a day, it doesn't matter what we eat. But that's not true," she concluded.

"None of these products undergo rigorous testing to verify how they affect our gut bacteria ," Spector cautioned. She also noted that additive and sweetener evaluation systems have not been updated for more than half a century. So what works?

Tim Spector's final message is forceful: the key to sustainable weight loss lies in diet , not exercise. While he emphasizes that physical activity is essential for overall health —it improves mood, protects the heart, and even reduces the risk of cancer—he warns that it shouldn't be considered an effective tool for weight loss. His recommendation is clear: stay away from "zero" drinks, ultra-processed "light" foods, and apps that promise miraculous results , and instead focus on real food , with natural and fermented products , bitter flavors, and a more conscious relationship with what we eat .