An international group of scientists analyzed data from more than four thousand people across six continents and concluded that the key role in the spread of obesity is played not by a decrease in physical activity, but by an increase in calorie consumption. The results of the study were published in the scientific journal Proceedings of the National Academy of Sciences (PNAS). The authors compared the energy expenditures of residents of industrialized countries with those of people leading traditional lifestyles, including hunter-gatherers and rural communities. It turned out that residents of developed countries expend roughly the same amount of energy, despite a less active lifestyle. The main difference, according to the researchers, lies in nutrition. The modern diet contains significantly more ultra-processed foods — ready meals, snacks, sweets, and other products high in sugar, saturated fats, salt, and calories. The scientists found a link between high consumption of such foods and increased fat mass. In their opinion, it is the changes in dietary structure that more significantly explain the rapid rise in the number of people with obesity than a lack of physical activity. At the same time, the researchers emphasize that physical activity remains a crucial component of a healthy lifestyle. Regular exercise helps maintain heart and vascular health, preserve muscle mass, reduce the risk of chronic diseases, and positively affect mental well-being. The authors of the study believe that the results could influence strategies to combat obesity. While the main focus was previously on increasing physical activity, specialists now suggest paying more attention to the quality of nutrition, limiting ultra-processed foods, and increasing the availability of fresh and healthy products. According to the scientists, effective obesity prevention should combine two approaches — sufficient physical activity and balanced nutrition. However, today, diet likely plays a more important role in preventing weight gain.