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Think an expanding waistline is inevitable with age? Think again — at least until you're in your 60s.

A groundbreaking new study from researchers at Duke University has challenged everything we once thought about metabolism. A team led by Herman Pontzer, PhD, an evolutionary anthropologist at Duke University and author of the new book, "Burn: New Research Blows the Lid Off How We Really Burn Calories, Lose Weight, and Stay Healthy" found that metabolism stays steady from ages 20 to 60 and, shockingly, life changes like puberty, pregnancy, and menopause do not account for any shift.

Researchers looked at the data of more than 6,400 people in 29 countries around the world — aged 8 days to 95 years — and analyzed their total daily energy expenditures (calories burned) and found that metabolism peaks around age 1 and then slowly declines about three percent a year until age 20. Then, it stays the same until about age 60, before beginning to slowly decline again by less than one percent annually.

The findings were published in the journal Science in August.

Then Why Do So Many People Gain Weight After 40?

The study suggests a change in hormones, physical activity levels, and food consumption could be to blame. Processed foods with added sugars (breads, cereals, instant oatmeal) can add unwanted (and unknown) calories to your diet.

Do Metabolism Supplements Work?

Save your money and hit the gym instead.

"Metabolism-boosting supplements and 'superfoods' and all these diets...I wish we'd move away from that," Pontzer said. "The metabolism-boosting supplements don't work, and they really just don't. We need to get back to basics, get away from processed foods. Focus on foods that are high protein, high fiber, whole foods, and that's going to be the best way to manage your weight."

Do Men Have Higher Metabolisms Than Women?

Pontzer says that men do tend to burn more calories than women because men tend to be bigger and carry more muscle and less fat.

"But after you account for that difference in size and fat percentage, men and women's metabolism are the same, actually," he said. "There's nothing special about men's metabolism that makes them faster. It's just that they tend to be bigger, and we know that bigger people, you've got more cells cooking along, you're going to burn more calories just by being bigger."

Is There Anything I Can Do to Stop Weight Gain in Middle Age?

Pontzer says it's all about the diet. In fact, he believes it's more important than exercising.

"Exercise for health is super important, but diet is your best tool for weight loss, for weight management," Pontzer said. "In a way, [these findings are] really empowering because it says there's not some invisible force that's forcing you to gain weight. Instead, we can take control of our diet, focus on the calories that we're taking in and take control of our weight that way."


Is This the Key to Ultimate Hydration?

See how electrolytes work in your body.

Is This the Key to Ultimate Hydration?

Whether you're trying to stay hydrated for your workout routine or rehabilitation, recovery and hydration is so important to keeping your body performing like it should. So how do you make sure that happens? You need electrolytes — the minerals that give electrical power to your body. What the video below to see how they get to work inside your body and how you seamlessly add them to your day.

Presented by USANA.