How to Improve Your Metabolism: What Works, and the Myth to Drop First

Published on 24 September, 2026

Almost everything people believe about metabolism is a variation on one idea: that it slows down in your thirties and that is why the weight arrives. The largest study ever conducted on human energy expenditure found that this is not true.

What Metabolism Is Made Of

Total daily energy expenditure has four components, and they are very unequal in size.

Component	Roughly what share	Can you change it?
Basal metabolic rate—keeping you alive at rest	About 60 to 70%	Indirectly, by changing body composition
Non-exercise activity—fidgeting, standing, walking about	Highly variable, 15% or more	Yes, and this is the most underrated one
Thermic effect of food—digesting and processing what you eat	Around 10%	Modestly, through protein
Deliberate exercise	Often only 5%	Yes, but it is a smaller slice than people assume

Two conclusions follow from that. Basal rate dominates, and it is largely set by how much lean tissue you carry. And deliberate exercise is a smaller share of the total than almost anyone expects, which is much of why exercise alone is a weak weight-loss tool.

The Myth: It Slows in Your Thirties

In 2021 a study in Science analyzed total energy expenditure measured by doubly labeled water—the reference method, which tracks energy use in free-living people rather than estimating it. The dataset covered males and females from eight days old to 95 years.

Once expenditure was adjusted for fat-free mass, four distinct life stages emerged. Energy use rises sharply in infancy, peaking around one year at roughly 50 percent above adult levels. It declines slowly to adult levels by about age 20. It then remains stable from 20 to 60—including during pregnancy. Only after 60 does it begin to decline.

There is no metabolic slowdown in your thirties or forties. If weight has crept on since your twenties, the explanation is elsewhere: less movement, less muscle, more calories, worse sleep, more sitting. Those are all addressable, which is better news than a slowing metabolism would have been.

What Actually Sets Your Rate

Fat-free mass is the main determinant of basal metabolic rate—muscle, organs, bone and everything that is not fat. Larger people have higher metabolic rates, and people with more muscle have higher rates than people of the same weight with less.

This is why the practical answer to raising your metabolism is unglamorous and slow: build and keep muscle. It is also why crash dieting is counterproductive, since rapid weight loss without resistance training takes muscle along with the fat and lowers the rate you were trying to raise.

What Genuinely Helps

Build muscle

Resistance training two or more times a week, covering the major muscle groups. The direct calorie effect of extra muscle is often overstated—a pound of muscle burns only a few calories a day at rest—but the wider effect is real: better insulin sensitivity, more glucose disposal, better preserved rate during weight loss, and more capacity to be active.

Eat enough protein

Protein has the highest thermic effect of the three macronutrients, meaning a greater share of its energy is used in digesting and processing it. Research continues on how animal and plant-based proteins differ in this respect during the post-meal period.

The effect is modest on its own. Combined with protein's advantages for fullness and for preserving muscle during weight loss, it is the dietary change with the strongest claim here.

Move more outside of exercise

Non-exercise activity thermogenesis covers everything that is not sleeping, eating or deliberate exercise—walking to the shop, taking stairs, standing, cooking, fidgeting. It varies enormously between people and can account for a substantial share of daily expenditure.

It is also the most responsive thing on this list. A desk job with a car commute and an evening on the sofa produces a very different daily total from the same person taking stairs, walking at lunch and standing periodically. No gym membership is involved.

Sleep properly

Short sleep reduces insulin sensitivity, increases appetite and reduces spontaneous movement the following day. It affects both sides of the equation, and it is usually the first thing to go when people start trying harder.

What Does Not Work

Metabolism-boosting foods. Green tea, chilli, ginger and caffeine all produce small, short-lived increases in energy expenditure that are far too small to affect body weight. Drink them because you like them.
Eating small frequent meals. The idea that frequent eating keeps the metabolic fire burning does not hold up. Total intake determines the thermic effect, not how it is divided.
Breakfast as a metabolic trigger. Eating breakfast has no special metabolic property. Whether it suits you is a separate and legitimate question.
Cold exposure. Cold does activate brown fat and raise energy use, and the amounts involved are small in adults. Cold showers have other arguments for them; weight is not a strong one.
Supplements sold as metabolism boosters. No supplement meaningfully raises metabolic rate at safe doses. The ones that did were withdrawn for being dangerous.

Why Losing Weight Lowers Your Metabolism

This is worth understanding because it explains a great deal of frustration.

When you lose weight, energy expenditure falls for two reasons. There is less of you to maintain, which is simple arithmetic. And the body reduces expenditure somewhat beyond what the size change alone predicts, an effect called adaptive thermogenesis.

The practical consequences: the intake that produced weight loss stops producing it, which is a plateau rather than a failure. Resistance training and adequate protein reduce how much muscle is lost and therefore how far the rate falls. And losing weight gradually generally preserves more lean tissue than losing it fast.

When Something Else Is Going On

Occasionally a genuinely low metabolic rate has a medical cause, and it is worth ruling out rather than assuming.

An underactive thyroid, which typically comes with fatigue, cold intolerance, dry skin, constipation and hair changes. A simple blood test settles it
Polycystic ovary syndrome, which affects insulin sensitivity and weight regulation
Cushing's syndrome, which is rare but has a characteristic pattern
Certain medications, including some antidepressants, antipsychotics, steroids and beta blockers

See a doctor if weight has changed significantly without a change in habits, or if fatigue, cold intolerance or other symptoms accompany it.

Where This Fits in a Wellness Routine

The honest summary is that you cannot do much to your metabolic rate directly, and you can do a great deal about the components around it. Build muscle, eat enough protein, move throughout the day rather than only in a scheduled hour, and sleep properly.

That is less exciting than a metabolism-boosting food, and unlike the food it actually works. It is also worth putting down the belief that your body turned against you at 35. The data say it did not.

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FAQs

Q: Does metabolism slow down with age?

A: Not in the way people believe. A large study using the reference method for measuring energy expenditure found that, adjusted for fat-free mass, metabolic rate is stable from age 20 to 60 and only declines after that. The changes most people notice in midlife come from muscle, movement and intake instead.

Q: What is the best way to increase metabolism?

A: Build and keep muscle, since fat-free mass is the main determinant of basal metabolic rate. Beyond that, eat enough protein and increase everyday movement, which varies more between people than deliberate exercise does.

Q: Do metabolism-boosting foods work?

A: Not to any meaningful degree. Green tea, chilli, caffeine and ginger produce small, short-lived increases in energy use that are nowhere near large enough to affect body weight.

Q: Does eating small frequent meals speed up metabolism?

A: No. The thermic effect of food depends on total intake, not on how many times you divide it. Meal frequency is a question of what suits you rather than of metabolic rate.

Q: How much protein should I eat?

A: More than most people do, particularly when losing weight or over the age of 50. Protein has the highest thermic effect of the macronutrients, keeps you fuller, and preserves muscle while you lose fat. Your doctor or a dietitian can set a target for your situation.

Q: Why has my weight loss stalled?

A: Partly arithmetic—a smaller body needs less energy, so the intake that produced loss stops producing it. Partly adaptive thermogenesis, where expenditure falls somewhat further than size alone predicts. A plateau is expected rather than a failure.

Q: Does building muscle really burn more calories?

A: Less directly than the claims suggest, since a pound of muscle burns only a few calories a day at rest. The real benefits are better glucose handling, preserved metabolic rate during weight loss, and more capacity to be active.

Q: Can a slow thyroid be causing my weight gain?

A: It can, and it is easily checked with a blood test. Look for fatigue, cold intolerance, dry skin, constipation and hair changes alongside the weight. See a doctor rather than assuming either way.

Q: Do cold showers boost metabolism?

A: Cold exposure does activate brown fat and raise energy use, but the amounts in adults are small. There may be other reasons to take cold showers; weight is not a strong one.

Q: Is it true that crash dieting wrecks your metabolism?

A: Wrecks is too strong, but rapid weight loss without resistance training takes muscle along with fat, which lowers the rate you were trying to protect. Losing weight gradually with adequate protein and strength work preserves more lean tissue.

Sources

Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science, 2021. PMID 34385400
Dehnavi Z, et al. How animal and plant-based proteins affect energy metabolism during the postprandial phase in overweight and obese men: a cross-over study. Nutrition Journal, 2025. PMID 40259349
Beauregard N, et al. Exploring inter-individual variability in the thermic effect of feeding among women approaching menopause. British Journal of Nutrition, 2026. PMID 41919385

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