Does Your Metabolism Really Slow Down With Age?

“My metabolism slowed down” is one of the most common explanations for weight gain in midlife. A large study of how many calories people burn across the whole lifespan gives a more surprising answer. This guide explains what it found and what it does and does not mean. It is general education, not medical advice.

The study

In 2021 a team led by Herman Pontzer published a study in Science using data on more than 6,400 people from 29 countries, ranging from newborns to people in their 90s. Everyone had taken part in a “doubly labeled water” test, a gold-standard method that measures how much energy the body uses over one to two weeks while people go about normal life.

The results

After adjusting for body size and for how much lean tissue a person has, four phases showed up:

• Infancy: energy use is highest relative to body size, peaking around age one at roughly 50 percent above an adult’s.
• Childhood to about age 20: it slowly declines.
• Ages 20 to 60: it stays remarkably stable. There was no slowdown in the 30s, 40s or 50s, and the turning points did not line up with familiar milestones such as puberty or menopause.
• After 60: it begins a slow decline of less than 1 percent a year, about 0.7 percent, which adds up over decades.

Why this surprised people

Many assume metabolism drops steadily from the 30s onward, and that this alone explains gradual weight gain. This data suggests that, adjusted for body size and composition, adult metabolism is more constant than that. Adolescence, often described as a high-metabolism stage, did not stand out as a turning point either.

What it does not mean

• It does not say weight is easy to manage. The study measures how much energy people burn, not how much they eat, how they sleep or how their environment changes. Habits, stress, schedules and food availability can change a lot between 25 and 55.
• It does not cancel what happens after weight loss. Research on plateaus and the set point shows that the body does adjust after someone loses weight. That is a separate effect from age.
• The adjustment matters. The figures account for body size and lean tissue. Losing muscle with age, which is common, can still lower how much energy the body uses.

What this means in practice

• Muscle is worth protecting. Lean tissue uses more energy than fat tissue. Our guide to strength training for beginners is a place to start.
• Look at habits, not only metabolism. If your weight has crept up over the years, changes in activity, sleep and eating patterns are more likely contributors than a hidden slowdown.
• After 60, energy needs do shift. A slightly lower need is normal, and a clinician or dietitian can help with food and activity at that stage.
• Be wary of “boost your metabolism” products. If adult metabolism is this steady, there is not much room for a supplement or trick to change it.

The takeaway

For most of adult life, the calories your body burns do not follow the steady decline people expect. Age matters more from about 60. If weight has changed over the years, the explanation is usually broader than metabolism alone, and that is good news, because habits are something you can adjust.

Sources

• Pontzer H, et al. Daily energy expenditure through the human life course. Science, 2021.
• Duke University, Duke Population Research Institute, summary of Pontzer and colleagues’ work on metabolism through the life course.