"Our analyses suggest that increased energy intake has been roughly ten times more important than declining total energy expenditure in driving the modern obesity crisis."

"[In a sub-analysis of the diets of some of the groups from both highly and less-developed nations, the scientists found a strong correlation between the percentage of daily diets that consists of] ultra-processed foods -- [which the study's authors define as] industrial formulations of five or more ingredients -- [and higher body-fat percentages]." 

Study on Obesity Factors, Duke University, North Carolina

The research, published in PNAS, suggests diet, not inactivity, is the primary driver behind increasing obesity rates in developed countries. (Photo by Anastasia Shuraeva)

 

"Despite decades of trying to understand the root causes of the obesity crisis in economically developed countries, public health guidance remains stuck with uncertainty as to the relative importance of diet and physical activity."

"This large, international, collaborative effort allows us to test these competing ideas. It’s clear that changes in diet, not reduced activity, are the main cause of obesity in the U.S. and other developed countries."

Herman Pontzer, principal investigator with the Pontzer Lab, professor, Department of Evolutionary Anthropology, Duke University

 

"While we saw a marginal decrease in size-adjusted total energy expenditure with economic development, differences in total energy expenditure explained only a fraction of the increase in body fat that accompanied development."

"This suggests that other factors, such as dietary changes, are driving the increases in body fat that we see with increasing economic development."

Amanda McGrosky, Duke postdoctoral alumna, study lead investigator, assistant professor of biology, Elon University 

Professor Herman Pontzer and his co-authors, 80 in number, set out to gather data on obesity from labs globally. Data for 4,213 men and women representing 34 countries or cultural groups resulted, representing the full spectrum of socioeconomic groups. Total daily energy expenditures for everyone  was calculated, along with their basal energy expenditure (number of calories burned during basic biological operations and physical activity energy expenditure). 

 

Few large-scale studies have focused on comparing energy expenditure among populations among whom obesity appears common, as opposed to those resistant to obesity. Dr. Pontzer noted that understanding the relative contributions of diet and physical activity is vital if science aims at fully comprehending obesity's origins, in a bid to educate populations how best to avoid obesity and with it, the rise of diabetes, heart disease and stroke. 

 

People in traditional cultures among developing nations, do not tend to succumb to obesity. The recently published study out of Duke University sought to clarify what it was that exposed populations to greater incidents of obesity. Published in Proceedings of the National Academy of Sciences of the United States of America (PNAS), this study, using data on metabolic rates and energy expenditure among over 4,000 individuals from dozens of countries across a broad spectrum of socioeconomic conditions quantified calories that people from various cultures burn daily.

 

Common wisdom had it that people in highly developed nations are relatively sedentary, thus burn far fewer daily calories than those living in less industrialized countries, increasing the risk of obesity, and this is the message that public-health authorities have issued, in persuasive messaging on the necessity to ensure that sedentary lifestyles not take over lives, that it is critical for optimum health at all ages, to move about, exercise the body as well as consuming a healthy diet.

 

This new study finds otherwise. Concluding that Americans, Europeans and people in other developed nations expend roughly similar total calories most days, as did hunter-gatherers, herders, subsistence farmers, foragers and all those living in pre-industrialized nations. A finding that was unexpected in its conclusion that inactivity is not, after all, the major cause of obesity that it has been taken to be. 

 

It seems intuitive that comparing the energy expenditure of hunter-gatherers and farmer-herders opposite office workers would find a huge deficit on the part of the latter as opposed to the former.  It was established however that, though the hunter-gatherers and other primitive groups moved far more frequently throughout the course of a day than would a typical individual in a post-industrial society, overall daily calorie expenditure were closely analogous. 

 

A theory first proposed by Dr. Pontzer known as the constrained total energy expenditure model, posits that our brains and bodies closely monitor our total energy expenditure, keeping it within a narrow range. Should we begin consistently burning more calories for any reason for days on end, our brains slow down or shut off some tangential biological operations that sees overall daily caloric burn remaining in a consistent band.

 

The final takeaway from the study is, quite simply, the observation that within populations too much food is being consumed, in excess of the body's actual needs. As well, consuming the wrong types of food --ultra-processed, convenience and fast-food products, perhaps lacking in nutrients but packed with flavour enhancers, leading to higher body-fat outcomes. 

 

A new study concludes diet is by far the most important driver of obesity in more economically developed countries.  thebigland88/iStock

 

More than 1 billion people worldwide live with obesity, a global epidemic that health authorities have blamed on both increased consumption of calories and decreased physical activity. But which factor contributes more? After measuring the calories burned by people from different economic backgrounds and lifestyles, research published today in the Proceedings of the National Academy of Sciences concludes diet plays a far bigger role than physical inactivity in driving the epidemic—though not everyone agrees with that interpretation."

"The new study found that, when adjusted for body size, people in more economically developed societies expend relatively less energy. However, the differences are too small to explain the higher rates of obesity in these societies. Worldwide weight gains instead seem to be associated mainly with how much we consume, not how much we burn off."

"The findings align with the current conventional wisdom that increased energy intake is the primary driver of obesity and highlight the need for policies to reduce that, says Vanessa Oddo, an epidemiologist at the University of Illinois Chicago who was not involved in the work. However, she and others caution the study—which relied on computer modeling, one-off observations of study participants, and indirect measures of physical activity and diet—isn’t set up to pinpoint the epidemic’s causes."

Science Adviser