Lifestyle

What Happens to Your Metabolism After 50 That Most People Don’t Realize

By Curtis Jones · October 18, 2026

Ask most people why their pants fit tighter at 55 than at 35 and they’ll blame a slowing metabolism. A large 2021 study says that’s mostly wrong, at least until your 60s.

In 2021, an international team that included Duke University’s Herman Pontzer pooled measurements from more than 6,600 people ranging from one week old to age 95 in 29 countries. They used the doubly labeled water method, a urine test considered the gold standard for measuring how many calories people burn in ordinary daily life. The results, published in the journal Science, overturned some common beliefs.

Your 50s are steady. After adjusting for body size and composition, the researchers found that daily energy expenditure remains stable in adulthood (20-60 yr). Duke’s summary says the middle decades, the 20s through the 50s, were the most stable. Several things can explain a thickening waistline in midlife, the summary notes, but the findings suggest a changing metabolism isn’t one of them.

The slowdown starts around 60. The study’s statistical break point landed at about age 63, with a likely range of roughly 60 to 66. After that, size-adjusted energy use fell about 0.7% a year. That’s gradual. Over ten years it works out to roughly 7%.

By your 90s, the gap is real. Duke reports that a person in their 90s needs 26% fewer calories each day than someone in midlife.

Lost muscle is only part of it. Muscle burns more calories than fat, and losing it may be partly to blame, the researchers say. But the team controlled for muscle mass and still saw the drop. “It’s because their cells are slowing down,” Pontzer told Duke. The paper also found that fat-free mass, which includes muscle, begins to decline around 60 along with energy use.

Muscle is still the part you control. The CDC’s guidelines for adults 65 and older call for at least 150 minutes of moderate aerobic activity a week, at least 2 days of muscle-strengthening activities, and balance activities. Brisk walking covers the first. For the second, the CDC says to work all the major muscle groups: legs, hips, back, abdomen, chest, shoulders, and arms. If the full amount is out of reach, the agency says some activity is better than none.

Your calorie target shifts. The National Institute on Aging, citing the Dietary Guidelines, says a woman over 60 who wants to keep her weight steady needs about 1,600 calories a day if she isn’t physically active, 1,800 if she’s moderately active, and 2,000 to 2,200 with an active lifestyle. For men the figures are 2,000 to 2,200, then 2,200 to 2,400, then 2,400 to 2,600. NIA adds that older adults often need fewer calories but more nutrients, which is why it pushes nutrient-dense foods.

A sudden change isn’t just age. A drift of 0.7% a year won’t leave you exhausted, always cold, and noticeably heavier within a few months. An underactive thyroid can. NIDDK says thyroid hormones control the way your body uses energy, lists fatigue, weight gain, and trouble tolerating cold among common symptoms, and notes the condition is more common after 60. A blood test can check.

So the real story is kinder than the myth. Your metabolism probably didn’t turn on you at 50. It starts a slow decline in your 60s. How much you move and how much muscle you keep are still up to you.

This article is for general information and is not medical or nutrition advice. Talk with your doctor before starting a new exercise program or if you notice unexplained weight changes or fatigue.