Overeating, not a lack of physical activity, is the primary driver of obesity in today’s world, according to a new international study published in the Proceedings of the National Academy of Sciences.
Obesity is a major contributor to global mortality and morbidity, responsible for over four million deaths and 140 million disability-adjusted life years annually.
To determine whether rising obesity rates are due to increased food intake or decreased physical activity as societies industrialise, researchers examined daily calorie expenditure, body fat percentage, and body mass index (BMI) in 4,213 adults aged 18 to 60. The participants came from 34 populations across six continents and represented a wide range of lifestyles and economies—including hunter-gatherers, pastoralists, farmers and office workers in industrialised nations.
The study found that obesity is largely driven by people consuming more calories than they burn. Physical activity levels remained remarkably consistent across populations, regardless of economic development. “There weren’t really any differences in total energy expenditure across these populations,” one researcher noted. “So, someone who lives in a hunter-gatherer society who has 40kg of lean body mass is going to expend the same energy as someone who lives in the US and also has 40kg of lean body mass.”
Among the 25 populations with available dietary data, higher consumption of ultra-processed foods—such as ready-made meals, packaged snacks and sugary drinks—was linked to greater body fat percentage.
While exercise may not be the primary factor in preventing obesity, researchers emphasise that regular physical activity remains crucial for overall health. It is linked to reduced risk of all-cause mortality, cardiovascular disease, certain cancers and improved mental well-being.
“Diet and physical activity should be viewed as essential and complementary, rather than interchangeable,” the authors concluded.
