Shedding Light on the Metabolism Mystery

By Rebecca Shrum

Empowering Health & Wellness

Some avid runners think that hitting the track, trail or street, day after day, “boosts” their metabolism. Is that perception true? Not according to a recent study published in Nature Communications. It found that:

    • Individual metabolisms vary by 20 percent or more from person to person regardless of activity level or body composition
    • Weighing in on the skinnier side of the scale is not evidence that you have a faster metabolism
    • Your individual metabolic rate—fast or slow—doesn’t vary over time.
    • Total energy expenditure — the total calories you burn every day– is a repeatable measure like height constitutes metabolism.

We think of exercise as putting our foot on the gas pedal of our metabolism. But think again!

The Skinny on Calories

The 300 adults in the database had their total energy expenditures measured twice, at times ranging from two weeks to more than eight years. The numbers were adjusted for body size and composition. More cells burn more calories and different types of cells (fat vs. muscle, for example) burn calories at different rates. The team judged whether someone had a “fast” or “slow” metabolism by determining whether they burned more or fewer calories than expected based on attributes.

Finally, when they looked at people’s daily energy expenditures over time, they found that the numbers didn’t really change. “If you’re a high-metabolism person, you’ll have that high metabolism for your body size today, and you’ll still have it in a few months or even a few years,” said Associate Professor of Evolutionary Anthropology Herman Pontzer, one of the study’s lead researchers. And yes, you guessed it, if you’re a slow metabolism person today, you’ll also have a slow metabolism in the future.

Which brings up the inevitable question: “Does having a slow metabolism mean you’ll gain weight?” No, and the research showed having a fast metabolism didn’t make people less likely to gain weight either. Pontzer attributed this eventuality to the human brain’s outstanding ability to match, over the long run, calories consumed to calories burned.

Exercise affects how our body regulates all of its cells and that, in turn, affects things like feelings of hunger and fullness, immune function, and even behavior. “I don’t think there’s a researcher out there who’s looked at the data and doesn’t understand how important exercise is for health,” Pontzer said. “But there’s an academic debate as to why it’s important for health.” Overall, he believes data doesn’t support exercise as being central to weight control.

You Are What You Eat

If exercise isn’t your silver bullet, what is? Pontzer points to diet as the biggest lever you must pull when it comes to managing weight. Easier said than done. “The food environments that we’ve built for ourselves really make it hard for people to maintain a healthy bodyweight,” he said.

The good news is that physical activity does seem to have an effect on regulating consumption—those who exercise are, in broad terms, less likely to overeat than those who don’t. The bottom line? Run on, peeps, run on!

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