Diet not lack of exercise drives obesity, a new study finds : NPR

A new study shows that people in countries with different obesity rates burn roughly the same number of calories.

PCH-VECTOR / ISTOCPHOTO / GETTY images

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PCH-VECTOR / ISTOCPHOTO / GETTY images

In the 1800s, obesity was almost nonexistent in the United States. During the last century, it became common here and in other industrialized countries, although it remains rare in people who live more traditional lifestyles, such as Hadza hunters in Tanzania.

So what changed? A current explanation is that, as companies have developed, they have also become more sedentary and people have become less active. The hypothesis is that in consequence, we burn fewer calories every day, contributing to an energy imbalance that leads to weight gain over time, explains Herman Pontzer, professor of evolutionary biology and global health at the Duke University which studies how human metabolism has evolved.

But in a new major study published in the journal PNA, Pontzer and an international team of employees found that this was not the case. They compared the burning of total daily calories for people from 34 countries and cultures different from around the world. The people involved directed the spectrum of hunter-gatherers and agricultural populations with low obesity rates, to people in more sedentary jobs in places like Europe and the United States, where obesity is widespread.

“Surprisingly, what we see is that in fact, the total calories burned per day are really similar in these populations, even if the lifestyle and the activity levels are really different,” explains Pontzer.

And that the observation offers solid evidence that diet – not a lack of physical activity – is the main engine of weight gain and obesity in our modern world.

“This steals in a way against what many of us supposed anecdotally leading a large part of the weight gain and obesity today,” explains Deirdre Tobias, an obesity and a nutritional epidemiologist at the Brigham and Women’s hospital in Boston and the Harvard Chan School of Public Health. Tobias was not involved in the new research.

Different activity levels, same caloric burn

In the study, researchers examined data of more than 4,200 adult men and women. Study participants received special drinking water that contained isotopes that came out in their urine. These isotopes allow scientists to determine exactly the amount of energy that a person spends – not only in active movement, but also the energy necessary to keep our hearts beating, our nervous systems working and generally remains alive.

“This allows us to get a really precise measure of the number of calories that people burn per day for about a week,” explains Pontzer.

When they adjust for body size, Pontzer and his colleagues found that people of populations with higher obesity rates burned only slightly less total energy per day than those of the populations who weighed less. These differences in energy expenditure did not contribute much to the differences in obesity rate between the populations, he says.

Although it may seem improbable that someone who houses berries all day burns about the same quantity of daily calories as, say, your typical office worker, Pontzer says that it corresponds to what scientists have learned about how our bodies burn calories. Pontzer’s previous research has suggested that our body tends to adjust the way we spend energy to maintain our stable caloric burn in a fairly narrow beach.

“So, if we burn more our energy every day on physical activity, in exercise, after a certain time, our body will adjust and spend less energy for the other tasks that we do not notice in the background,” explains Pontzer.

Change the message on obesity

New discoveries have great implications for obesity. If calories burning differences cannot explain why some countries have higher obesity rates than others, then it should be something else. “And it would be a diet,” said Tobias, who praised the conception of the new study.

“It is 100% the regime,” said Dr. Dariush Mozaffarian, director of the Food is Medicine Institute of the Friedman School of Nutrition Science and Policy from Tufts University. “And I then think that the question is: What is the diet?”

Mozaffarian was not involved in the study, but he says that this adds to other recent research that suggests that food is the largest engine of obesity. He underlines that there has been a major change in our food supply in recent decades – which is now dominated by ultra -treated food. In a signanelysis of data for certain populations, Pontzer and its colleagues found that the inhabitants of countries who obtained more of their calories from ultra-transformed foods tended to have more obesity and percentages of higher body fat.

“For decades, we have told Americans that you are lazy, it’s your fault, you don’t move enough, you eat too much,” said Mozaffarian. “And I think that this study shows is that there is really a complicated biology and that our food is originally.”

Now that does not mean that there is no reason to exercise. After all, it’s good for our mental and physical health in many ways that have nothing to do with weight.

But that means that we cannot exceed poor diet. Pontzer says that if we want to fight obesity, the public health message should focus on changing what is on our plates.