Everything You Thought You Knew About Burning Fat Is Wrong

Everything You Thought You Knew About Burning Fat Is Wrong


For decades, the experts’ line on exercise and weight loss was simple: Do this much, lose that much. But recently they’ve changed their tune: While exercise is awesome for overall physical and mental health, they say, don’t expect it to necessarily yield the number one result most guys want when they join a gym.

Why the switch? More than anything, it comes down to Hadza piss.

The Hadza are hunter-gatherers in East Africa who get more exercise in a day than many of us get in a week. When scientists set out to measure the caloric cost of all that hunting and gathering (plus everything else requiring energy), they had them drink water laced with two rare isotopes. After checking the peed-out isotopes and comparing the ratio of one to the other, they could tell how much CO2 the Hadzas produced during that time and, by extension, how many overall calories they burned.

“I came into this research assuming that the more activity you get, the more calories you burn,” says Herman Pontzer, Ph.D., an anthropologist at Hunter College and one of the architects of this paradigm-changing research. He’d also assumed the converse—that the more time you spend sitting, the fewer calories you burn. So when he conducted a pissing match between the lean-and-hungry Hadza and sedentary office workers, the results shocked him. After accounting for body size, the office slugs had the same energy expenditure as guys who chase giraffes for a living.

Pontzer says it’s the same across species. The daily calorie burn of a caged zoo animal is the same as that of its born-free counterpart in the Serengeti. Apparently the more active you are, the more your metabolism adjusts to balance the caloric ledger.

What all this means is that no matter how many calories a normal guy burns with exercise, his body will find ways to restrict the number he burns the rest of the day. When researchers compared sedentary people to moderately active people, the active group burned only about 200 more calories a day overall, even at higher activity levels. That’s a far cry from the numbers you see on your fitness tracker. Pontzer calls this “constrained energy expenditure.” And your metabolism has lots of room for adjustment, given that 50 to 70 percent of energy expenditure goes toward the basic functions of staying alive, 10 percent goes to digesting food, and the rest (20 to 40 percent) is for physical activity.

Depressing? Yes, especially for the millions of Americans who probably wouldn’t work out at all if they didn’t think it would help them lose weight. But is it really the final word? Not necessarily.

What Is Energy Flux?

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Mick DiMaria is a small-framed, 5’7″ creative director and writer in Southern California. He kept his weight steady for most of his adult life without much effort, gaining about 10 pounds during the holidays and losing it after the start of the new year. “But in my 40s, it wasn’t so easy to lose it,” he says. At 174 pounds, he was way below the 196-pound national average for men. Still, he says, “I was pushing maximum density.” So he hired a trainer. Although his initial focus was on building muscle, he started losing weight, averaging a half pound a week. After a little over a year, he was down to 147.

To look at DiMaria today, you’d never guess he’s 24 pounds lighter. And if you did, you would assume it was because he drastically changed his diet. But he says those changes were modest, like eating more whole foods and making his lunches instead of getting takeout. “I never skipped meals,” he says. “I never gave up anything. I just had less of it.”

“I strongly believe that exercise can contribute to weight loss.”

DiMaria is hardly the only one. Every trainer has at least one client like him, someone whose body never got the memo about exercise being ineffective for weight loss. You’ve probably seen it yourself—the cousin who started working out in his basement and lost his gut, the neighbor who shed 10 or 20 pounds by walking around the block.

“Exercise just by itself isn’t going to work for the majority of the population. But there are smaller subsets where we see it,” says Brian St. Pierre, M.S., R.D., director of performance nutrition at Precision Nutrition. How rare are these subsets? What do these people have that makes them exceptions to the new research? And for your purposes, can you turn yourself into an exception, or must you be born that way? At least one researcher says we may have more control than we think.

“I strongly believe that exercise can contribute to weight loss,” says Clemens Drenowatz, Ph.D., a professor of physical education at the University of Education, Upper Austria. One reason is a concept called “energy flux,” or the speed of energy turnover in the body.

How Energy Flux Works

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Imagine three guys with stable body weights. Two of them have the same daily energy expenditure—say, 3,000 calories. They are both “high flux,” meaning they take in a lot of calories and burn a lot of calories. But their bodies burn energy very differently. The first guy moves more, both intentionally (by exercising) and unintentionally (by fidgeting and spending more time on his feet). The second guy is pretty sedentary; he has an office job and doesn’t exercise much. However, the second guy’s heavier body requires more energy for movement and just staying alive. So at the end of the day, assuming their calorie intakes remain the same, neither of the two puts on or loses significant weight.

Now consider the third guy. He’s low flux, meaning he takes in and burns fewer daily calories than the other two, but he’s also established an equilibrium and his weight remains stable.

Early research from way back in the 1950s suggested that people who move the least may consume more calories than they expend. The more exercise a person gets, the easier it could be to avoid weight gain.

Understanding the concept of energy flux may be the key to understanding the secret of weight loss.

But something else happens at the extremes, something scientists still don’t fully understand. Paradoxically, the higher the numbers (calories in/calories out), the leaner you may be and the easier it may be to control fat.

It’s borne out by a three-year American Journal of Clinical Nutrition study of teenagers, published in 2016. The scientists found that teens who ate a lot of calories and burned a lot of calories reduced their body fat percentage over those three years, while those who ate little and burned little gained fat. This is despite the fact that teens in the high-flux group were eating several hundred more calories a day than they needed to maintain their weight at the start of the study, while the low-flux teens were eating below maintenance. The combination of high intake and high expenditure was somehow more powerful than either variable in isolation, making them leaner than they should’ve been.

Why Is Your Body in Flux?

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As Drenowatz proposed in a 2017 research review, the quantity of calories people consume is independent of the amount of exercise they get. An active person who becomes sedentary may eat the same amount as before (if not more than necessary) and gain a lot of weight. The extra body mass then raises his metabolism, since it takes more energy to maintain a bigger body. That, in turn, leaves him with the same energy flux he had when he was smaller and more active.

Why would your body do this? Drenowatz thinks the human body seeks a preferred energy flux rather than a preferred bodyweight. Indeed, studies of identical twins have shown that they typically have the same flux, even when their body weights and activity levels differ. The higher body mass of the less active twin allows him to burn the same number of calories as his lighter sibling.

Pontzer says it’s possible that high or low daily energy expenditure is set early in life, although we don’t know what the precise mechanism is. He’s noted two groups that appear to have high expenditure: athletes and subsistence farmers. What do they have in common? They both tend to grow up moving a lot and eating a lot.

Whether it’s genes, environment, or some combination, high expenditure in childhood may remain intact throughout life, but Pontzer says we don’t know for sure. Being predisposed to high energy flux may help some people respond quickly to workouts and have more success keeping their weight stable through exercise, while for some others no amount of exercise affects weight loss. Turns out, this can be the key to healthy weight.

Work Out, or Flux It?

To gauge if exercise could help you easily lose weight and keep it off, ask yourself if you fit into one or more of the following categories:

If any of these ring true, there’s a good chance you’re high flux. That suggests your body prefers to eat a lot of food each day, and until recently you matched your appetite with a high activity level. And it suggests your body may respond quickly to structured workouts.

The best exercise (no surprise) is whatever you like most and will do consistently. No preference? Drenowatz likes strength training. It increases energy flux four ways:

In total, Drenowatz recommends more than 300 minutes a week of exercise at a moderate to hard pace, which seems like a less popular guideline than, say, “walk 10,000 steps a day.” But it’s not hugely different from the program DiMaria used:

What if you do everything right and still don’t see a significant difference on the scale? “The data is really clear that exercise is super important for health,” says Pontzer. “The health issues that people deal with as they age [heart disease, type 2 diabetes, cancers], exercise helps with all of them.”

Drenowatz agrees, adding that the psychological benefits also matter. You feel better when you’re more active, and that in turn helps motivate you to make better food and lifestyle choices. Bonus: If you’ve already lost weight, exercise can help you keep it off.

So even if this basic workout template doesn’t help you lose a significant amount of weight, you don’t have anything to lose. The worst that can happen is you’ll get stronger, leaner, and healthier, which isn’t such a bad thing to settle for.

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