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Your Metabolism Doesn't Change Before 60

Weight gain in your 40s and 50s is caused by something other than age.

Key points

  • Metabolism actually stays steady from age 20 to 60, despite the belief that metabolism is faster in the 20s.
  • Pregnancy can cause lasting weight gain, and many medical issues in midlife can contribute to it as well.
  • Keeping the weight off in one's 40s and 50s usually requires reevaluating one's habits.

If you’ve been kicking yourself for putting on some pounds lately, you’re not alone. Many people cut back on exercise during the recent shutdowns and snacked on carbs and sweets during too many hours stuck in the house.

If you're in your 30s, 40s, or 50s, you might dream of your younger days, vaguely recalling a time in your 20s when you could eat a serving bowl full of pasta and not gain an ounce. That memory is probably wrong. New research published in August shows that our metabolisms stay very steady from age 20 to 60.

This was a particularly large study, drawing upon data from more than 6,400 participants of all ages from infancy to 95, pooling together 40 years of previous research.

The good news here is that you don't have to feel like you're fighting your body to stay slim just because you're 45 or 50. And even past 60, exercise is the secret of youth.

Unsplash/John Moeses
Source: Unsplash/John Moeses

What is metabolism?

Our bodies break down food and convert it to energy, a process called metabolism. The new research found that the process does change over the years—but not the way we thought.

Here’s what actually happens: At age 1, you were burning about 50 percent more energy than you would by age 20. As a child, your metabolism gradually slows down until it reaches your adult rate by age 20, where it stays until age 60, and then it begins to decline again.

Researchers used to think that metabolism slows down at 40 or even 30 and that men had a faster metabolism than women. But neither was true. Men do burn more calories in a day but only because they are larger and have less body fat, on average. A muscular woman will have about the same metabolism as a man of the same height. A 150-pound person with 15 percent body fat will have a higher metabolic rate than a 150-pound person with 25 percent body fat—even if they are the same age.

Overall, some people burn about a quarter less or a quarter more than the average rate for their age. But they still have the pattern of a constant rate from age 20 to 60.

Your resting metabolic rate (RMR) is the number of calories your body uses up if you do nothing for 24 hours.

Your basal metabolic rate (BMR) is the calories you need to accomplish your basic functions: breathing, circulation, nutrient processing, and cell production.

The two numbers are slightly different, but you can use either.

To measure your RMR, you need to measure your oxygen consumptions and carbon dioxide exhalation after sitting or lying down for at least 15 minutes, and you can’t have done any exercise in the previous 12 hours.

Online calculators, including this one from the National Institutes of Health, can give you a target number of calories per day to maintain your current weight.

It’s very hard to boost your metabolism

This study supports previous work that it’s very hard to change your metabolism. Don’t count on supplements like green tea to give you an edge so you can eat more cookies! What does help: resistance training that makes you more muscular. One study found that 10 weeks of resistance training can boost RMR by 7 percent. However, it’s easy to lose that muscle if you don’t keep up your efforts.

But why did I gain weight in my 40s?

The reason might be that you changed your habits. You got less exercise, slept less, or worked longer hours.

You might have developed medical problems: Type 2 diabetes, hypothyroidism, and polycystic ovary syndrome can all trigger weight gain.

Weight gain also can be triggered by stress, sleep issues, and medications that are associated with age.

Multiple pregnancies can lead to a pile-up of extra weight by your 40s. About half of all women gain too much weight while pregnant. Losing those pounds isn't automatic. Overall, your chance of developing obesity more than triples if you have a baby compared to women who don't.

Hormonal changes during menopause—typically beginning in the mid- to late-40s—make a difference. It’s common for women to get plumper in the middle.

So what can I do to keep my weight down?

April Laugh/Unsplash
Source: April Laugh/Unsplash

Most people need to eat less and exercise more. The book Lose It Forever: The 6 Habits of Successful Weight Losers from the National Weight Control Registry tells the stories of people in an ongoing study. To join, you must have lost at least 30 pounds and kept it off for at least a year. You can see a summary of the findings of the National Weight Control Registry here. Nearly all of the participants exercise every day—on average for about an hour, but the most popular exercise is walking.

A version of this story also appears on Your Care Everywhere.