You might feel the burn, but you won’t see it.
“We’ve all been told that the more active you are, the more calories you burn,” said Herman Pontzer, an evolutionary anthropologist and Duke professor whose new book, “Burn,”(Penguin) is out now. “But bodies aren’t simple engines. We’re evolved, complex beings,” he told The Post.
Pontzer, a Ph.D. who has spent his career studying energy expenditure among the Hadza tribe, a group of hunter-gatherers in northern Tanzania, claims that diet, and not exercise is the key to losing weight.
By taking urine samples to determine their rate of carbon dioxide production, Pontzer found that although the Hadzas have a much more active lifestyle than their urbanite counterparts — members of the tribe hunt for food, while office workers eat Seamless at their desks — both expend roughly the same amount of energy.
“We’re on fixed incomes,” Pontzer said of human physiology. “When you spend more energy on physical activity, the body spends less energy in other places.”
In other words: While working out can have plenty of positive effects — reducing joint inflammation and building strength, endurance and mental sharpness — it won’t do much to lower the number on the scale.
But not everyone agrees. “I wouldn’t go as far as to say exercise isn’t important in weight loss,” said Sean Heffron, a cardiologist who treats obesity at NYU Langone. “Exercise increases overall metabolism, which leads to further burning of calories, increases muscle mass and maintains lean tissue better, burning more energy in the long run.”
“It’s not quite as simple as calories in, calories out,” said Cordelia Carter, a sports medicine specialist at NYU. “Better cardiovascular fitness and strength training prevents being ‘skinny-fat’ or ‘fat but fit’ — both of which aren’t great.” Heffron suggests high-intensity interval training to get “the most bang for your buck” but agreed “without a change in diet, weight loss is not going to happen.”
Pontzer argues that even our understanding of ideal caloric intake is wrong-headed. “Nine-year-olds burn 2,000 calories per day; for adults, it’s closer to 3,000,” he writes. In Pontzer’s model of “constrained daily energy expenditure,” our bodies adjust how we spend our capped number of calories based on lifestyle.
A sedentary person’s body will use energy for “nonessential” bodily functions, like amping up stress responses. For a star athlete, massive physical energy expenditure will draw away calories from other systems, such as reproduction and immunity. This can lead to excessive fatigue and burnout known as “overtraining syndrome.”
Pontzer has a surprising takeaway: “You’re not in control of your metabolism,” he said.
That’s why he believes the only way to slim down is through diet. The Hadza tribe’s balanced, seasonal omnivore menu — with carb from grains, starch from tubers and sugar from honey — makes for a good example. He suggests eating protein- and fiber-rich meals that are satisfying and keep you full longer.
As Westerners, he said, we get overly caught up in excluding entire categories of food. “If you villainize certain foods, you get to these weird conclusions like, ‘An apple is bad for you because of the sugar content in fruit,’ ” he said. (One exception: processed foods, which Pontzer said, “blows our brains up … by overwhelm[ing] our brain’s reward systems.”)
He’s also suspicious of trendy low-carb, low-sugar “paleo” or “carnivore” diets, which claim to mimic the diets of hunter-gatherer tribes. In reality, Pontzer said that the Hadzas are not nearly so strict about what they ingest.
If your goal is to lose weight, Pontzer suggests reducing caloric intake by 3,500 calories per week, or 500 per day. He said this will result in weight loss at a rate of about a pound per week.
“Use diet to watch your weight,” he said unequivocally, “and exercise for everything else.”
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