Diet may trump exercise in tackling obesity for industrialized societies

Although rising obesity rates related to economic development have been linked to lower physical activity levels, new research suggests that higher calorie consumption is the primary driver of overweight and obesity in more industrialized societies.

Duke University’s Pontzer Lab (US) observational study found positive correlations between economic development, energy expenditure, obesity, and estimated energy intake. 

“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,” says Herman Pontzer, principal investigator with the Pontzer Lab and professor in the university’s Department of Evolutionary Anthropology.

“It’s clear that changes in diet, not reduced activity, are the main cause of obesity in the US and other developed countries.” 

Economic development impact

The researchers analyzed thousands of measurements of daily energy expenditure, body fat percentage, and body mass index for 4,213 adults from 34 populations across six continents. 

The study in PNAS Anthropology includes people from a wide range of lifestyles and economies, such as hunter-gatherer, pastoralist, farming, and industrialized populations. 

To categorize the level of industrialization, the researchers integrated data from the UN Human Development Index to incorporate measures of lifespan, prosperity, and education. 

The researchers note that when adjusted for body size, energy expenditures decreased around 6–11% with higher economic development. However, the authors warn that this was highly variable among populations and did not correspond closely with lifestyle. 

“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,” says Amanda McGrosky, a Duke postdoctoral alumna and lead investigator for the study. She is now an assistant professor of biology at Elon University, US.

The researchers underscore not to minimize the promotion of daily physical activity, as this has many well-documented health benefits.“This suggests that other factors, such as dietary changes, are driving the increases in body fat that we see with increasing economic development.”

At the same time, the authors caution that they lack detailed dietary data for most of the populations in their dataset. Therefore, they cannot establish causality between economic development, body fat percentage, and dietary intake, nor can they resolve environmental, societal, or physiological factors influencing these relationships. 

Diet vs. exercise?

The researchers underscore that despite diet’s central role in the obesity crisis, efforts to promote physical activity should not be minimized. They say daily activity has many well-documented health benefits and is essential to a healthy lifestyle. 

“Rather than advocating for diet over exercise in public health, data from this study join an emerging consensus that both must be prioritized. Diet and physical activity should be viewed as essential and complementary, rather than interchangeable,” reads the paper. 

However, the authors emphasize that their results highlight a need to identify factors linking foods in developed countries to increased obesity. 

For example, the team says their analysis linked a higher share of ultra-processed foods in the diet to increased body fat percentage among the 25 populations with available data on these foods. They found no significant association between per capita meat consumption and fat percentage in the same dataset. 

At the same time, the researchers say not all impacts of economic development and the adoption of the modern food system have been negative. They add that global supply chains ensure affordable food is available to almost every population. In addition, their study suggests that additional energy from food is channeled into healthy growth, as fat-free mass was higher in industrialized populations. 

“Regulating food environments to maximize the benefits of increased calorie availability without promoting a nutrient-poor, obesogenic diet remains a crucial challenge in public health that will only become more acute as economic development continues globally,” concludes the study.