Lack of physical activity is not likely to be a key factor in Western obesity rates, according to a new study published in the journal PLoS ONE, which suggests that over-consumption of calories is the biggest culprit.
Some researchers have suggested that the differences between Western lifestyles and the more active lifestyles of our hunter-gatherer ancestors may explain why obesity rates have skyrocketed in some parts of the world over the past few decades.
However, researchers from the United States, United Kingdom, and Tanzania are the latest to challenge this theory in a study that examined the total energy expenditure (TEE) of the Northern Tanzanian Hadza tribe of hunter-gatherers.
They hypothesized that the hunter-gatherers would expend more energy in their daily activities than those in market and farming societies – but that was not what they found.
“Contrary to expectations, measures of TEE among Hadza adults were similar to those in Western (U.S. and Europe) populations,” the researchers wrote.
Complex metabolic strategy
They did find that the Hadza people had higher levels of physical activity, but after controlling for body size and composition, their energy expenditure was statistically indistinguishable from that of Westerners, they wrote.
Their results suggest that energy expenditure may play a very small role in determining whether someone will become overweight, with a more complex metabolic strategy at work to respond to energy availability and demand. In other words, the most important cause of obesity is likely to be eating too much, rather than doing too little.
“The similarity in TEE among Hadza hunter-gatherers and Westerners suggests that even dramatic differences in lifestyle may have a negligible effect on TEE, and is consistent with the view that differences in obesity prevalence between populations result primarily from differences in energy intake rather than expenditure,” they wrote.
Physical activity’s importance for health
The researchers stressed that increased physical activity does have health benefits.
“Physical activity has important, positive effects on health, and increased physical activity has been shown to play an important role in weight loss and weight-maintenance programs,” they wrote. “Some studies of self-reported activity level have even suggested that habitual activity may help prevent unhealthy weight gain, although the evidence is mixed.”
The study is not the first to question physical activity’s role in weight maintenance. Researchers from the University of Deakin in Australia previously have suggested that US obesity is nearly exclusively caused by excess calorie intake, not lack of exercise.
However, this latest study is important because the researchers actually measured energy expenditure, using the doubly labeled water method, rather than relying on estimates.
The study may have implications for the food and beverage industry, which has taken a dual approach to tackling obesity. It has focused its efforts not only on product reformulation to reduce trans fats, saturated fats and sugar, but also on encouraging increased physical activity.
Source: PLoS ONE
7(7): e40503. doi:10.1371/journal.pone.0040503
Authors: Herman Pontzer, David A. Raichlen, Brian M. Wood, Audax Z. P. Mabulla, Susan B. Racette, Frank W. Marlowe