Lack of exercise or a high-calorie diet -- What causes obesity? Major new study offers surprising insight

Time of India

4 days ago

Couch potatoes have always had bad press.
But turns out, the over-the-top foodies are equally guilty – if not more.
Obesity, now a global public health crisis, has long been blamed on sedentary lifestyles and high‑calorie diets.
In 2025, global obesity rates are projected to continue rising, with estimates suggesting that one in five adults worldwide will have obesity.
This trend indicates that countries are significantly off track to meet the World Health Organization's (WHO) 2025 targets to halt the rise of obesity. What's more? The World Obesity Federation's 2025 Atlas highlights that many countries lack sufficient policies and plans to address the escalating obesity crisis.
Amidst that, a major new study published in
Proceedings of the National Academy of Sciences
sheds surprising light on the root causes.
Is it the sedentary lifestyle alone? Or is the high-calorie diet to be blamed for it?
Read on to know more.
The study
The new study, led by Dr. Herman Pontzer at Duke University, has flipped traditional ideas about the origins of obesity on their head, highlighting that our diets might hold more weight, literally and figuratively, than the amount of physical activity we engage in.
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Published this week in the Proceedings of the National Academy of Sciences (PNAS), the research challenges the long-held belief that individuals in developed countries like the United States of America lead relatively inactive lifestyles and consequently burn fewer calories. Surprisingly, it reveals that calorie-burning rates among people in developed nations are comparable to those of individuals in less industrialized regions, including farmers, herders, and hunter-gatherers who enjoy more active routines.
More specifically – the researchers calculated total energy expenditures for 4,213 men and women from 34 countries or cultural groups, and found they were similar, regardless of whether someone was an American office worker or a hunter-gatherer.
This groundbreaking research work, examining the energy expenditure and metabolic rates of those individuals from diverse nations, proposes that inactivity might not be a significant contributor to obesity in the US or beyond.
Instead, the study emphasizes that dietary choices play a much larger role than the decrease in energy expenditure associated with economic progress.
As per the study, what people eat 'plays a far greater role than reduced expenditure in the elevated prevalence of obesity associated with economic development.'
The experts' take
Herman Pontzer, a professor and senior author of the study, shared with the Washington Post that these findings are pivotal in helping health officials pinpoint the true causes of obesity, paving the way for more effective treatments.
Alongside more than 80 co-authors, Pontzer collected data from laboratories worldwide utilizing doubly labeled water in metabolism studies, a method that precisely measures energy expenditure.
Contrary to the notion that increasing exercise would lower obesity rates, the study reveals that 'increased energy intake has been roughly 10 times more important than declining total energy expenditure in driving the modern obesity crisis,' according to the authors.
In simpler terms, populations grappling with higher obesity rates are consuming excessive amounts of food, often the wrong types, as Pontzer explained.
Barry Popkin, a professor at the Gillings School of Global Public Health at the University of North Carolina at Chapel Hill and a recognized obesity expert, told the Post, 'This study confirms what I've been saying, which is that diet is the key culprit in our current [obesity] epidemic.'
He added that 'this is a well-done study,' a sentiment echoed by other professionals in the field.
Dariush Mozaffarian, director of the Food is Medicine Institute at Tufts University in Boston, stated, 'It's clear from this important new research and other studies that changes to our food, not our activity, are the dominant drivers of obesity.'
What's ahead, then?
As the study reveals, obesity's roots are multifaceted. The latest evidence confirms that while you can't outrun a bad diet, you can transform your health by choosing what and how much you eat. It is now a proven fact that proper diet plays a tad bit more important role in managing weight and keeping obesity in check than a laid-back lifestyle. Should we go back to our couches then, instead of picking up the dumbbells?
That doesn't sound wise.
This landmark study rather revolutionizes our understanding of obesity: metabolic adaptation buffers against exercise-driven calorie deficits, while poor diet remains the primary villain. To tackle the obesity epidemic, public health must realign – from 'move more' to 'eat smart.' Coupling smart eating habits with regular exercise provides the best defense.
In fact, Pontzer stressed that these findings do not diminish the importance of exercise for our overall health. 'We know that exercise is essential for health. This study doesn't change that,' he affirmed. However, he advocated that to tackle obesity effectively, 'public health efforts need to focus on diet,' particularly concerning ultra-processed foods, as Pontzer highlighted.
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