Does Your Metabolism Really Slow Down in Your 40s?

Is your metabolism really slowing down in your 40s, or is that just something everyone repeats? Here is what the largest energy-expenditure study measured, what does change in midlife, and a 4-week routine you can try.

In this article

1. Does your metabolism slow down in your 40s?
2. What did the biggest metabolism study actually measure?
3. What does change in midlife?
4. Why can weight still creep up in your 40s?
5. Can exercise and strength training speed up metabolism?
6. What could a 4-week midlife routine look like?
7. When should you see a clinician?
8. Frequently asked questions
9. Final thoughts
10. Sources and further reading

Does your metabolism slow down in your 40s?

Your metabolism does not appear to slow down in your 40s in the way popular belief suggests. A large 2021 analysis of doubly labelled water measurements found that daily energy expenditure, once adjusted for body size and composition, stayed stable from about age 20 to about 60, and only began to decline after that.

If muscle is on your mind, the guide on how fast muscle declines with age and whether you can slow it goes deeper.

That does not mean nothing changes. Body composition, sleep, movement and hormones can all shift in midlife, and the popular story lumps them under one word, "metabolism".

What did the biggest metabolism study actually measure?

The 2021 Science paper by Pontzer, Speakman and a large consortium measured total daily energy expenditure with doubly labelled water in 6,421 people from 29 countries, aged 8 days to 95 years. It is among the largest datasets of its kind, and it found four distinct life stages rather than a drop in the 40s.

Doubly labelled water is a laboratory method: a person drinks water containing two harmless isotopes, and researchers track how fast they leave the body to work out energy use over one to two weeks.

The four life stages

The authors adjusted for fat-free mass and fat mass. They reported that adjusted expenditure rose quickly in newborns and reached about 50% above adult values at around age 1. It then declined slowly and reached adult levels by about age 20.

From about 20 to 60 it stayed stable, even during pregnancy. After about 60 it declined. The authors' accepted manuscript puts that decline at about 0.7% a year.

The limits of the study

The study compared different people at different ages rather than following the same individuals, and it describes averages. Its data on resting metabolism in people aged 40 to 60 were sparse, and the authors said more measurements were needed to know whether resting metabolism starts declining earlier than total expenditure.

What does change in midlife?

In midlife, the best-documented changes are in body composition, sleep and hormones rather than in the energy cost of simply being alive. Muscle can decline with age, sleep can shorten, and the menopause transition has been linked with faster fat gain and lean mass loss in women. The table below sorts these by how strong the evidence is.

Muscle and strength

A 2012 quantitative review in Frontiers in Physiology (Mitchell and colleagues) pooled studies of muscle size and strength across adult life. It reported that strength falls faster than muscle mass, roughly 2 to 5 times faster in studies that tracked both. Many quoted rates relate to people around 75, not in their 40s.

Hormones and the menopause transition

The 2019 SWAN analysis (Greendale and colleagues, JCI Insight) measured body composition by DXA scan in women followed through the menopause transition. At the start of the transition the rate of fat gain roughly doubled and lean mass began to decline. Weight itself did not measurably accelerate.

This is observational, so it shows association, not cause. For related changes in sleep and exercise, see what happens to sleep and exercise tolerance in perimenopause.

Why can weight still creep up in your 40s?

Weight can creep up in your 40s without any drop in metabolism, because weight reflects the balance between energy in and energy out, and several things can nudge that balance. Changes in body composition, sleep, daily movement and eating habits can each play a part, often slowly enough to go unnoticed.

Sleep is one example. A 2017 systematic review and meta-analysis in the European Journal of Clinical Nutrition (Al Khatib and colleagues) found that partial sleep deprivation increased energy intake by about 385 kcal compared with control conditions. Total energy expenditure and resting metabolic rate did not change significantly. Only 11 studies with 172 people contributed, so treat it as a pointer.

Less planned exercise or a gradual drop in muscle may also play a part. These are plausible but depend on the person.

Can exercise and strength training speed up metabolism?

Exercise can help your body composition and health, but its effect on resting metabolism looks modest and uncertain. A 2020 systematic review and meta-analysis found that resistance exercise raised resting metabolic rate by a small amount, while aerobic and combined exercise showed no significant effect, and the studies were at high risk of bias.

The review (MacKenzie-Shalders and colleagues, Journal of Sports Sciences) included 22 studies, 18 of them meta-analysed, in adults under 65. It reported that resistance exercise increased resting metabolic rate by about 96 kcal a day compared with controls, with a wide confidence interval of 45 to 147 kcal.

That is a small and uncertain figure, so strength training is better framed as a way to keep strength, muscle and function than as a metabolism hack. For weekly amounts, see how much strength training you need each week.

No source here suggests that exercise alone cancels out poor sleep or guarantees weight loss. For adults aged 19 to 64, the NHS recommends at least 150 minutes of moderate activity a week plus strengthening activities on at least 2 days, and advises speaking to a GP first if you have a medical condition or have not exercised for some time.

What could a 4-week midlife routine look like?

A sensible 4-week routine for your 40s builds a baseline, adds two short full-body strength sessions, then gradually extends walking and sleep regularity. The aim is not to speed up metabolism but to track habits you can influence and see how you feel.

When should you see a clinician?

See a GP or other clinician if your weight changes without an obvious reason, or if you have persistent tiredness, sensitivity to cold or other new symptoms. The NHS says an underactive thyroid can cause tiredness and weight gain, and advises seeing a GP if you think you might have one.

The NHS lists symptoms including persistent tiredness, sensitivity to cold, weight gain, low mood, dry skin and hair, and heavier or irregular periods. It notes that symptoms are often mild and develop slowly, and that some are common and can have other causes, so they are worth checking.

Unexplained weight loss, large changes in weight, or fatigue that does not improve with rest are also reasons to talk to a clinician. A fitness tracker cannot diagnose any of this.

Frequently asked questions

At what age does metabolism start to slow down?

In the 2021 doubly labelled water study, size-adjusted total energy expenditure began declining at about age 60, then fell roughly 0.7% a year according to the authors' manuscript. Resting metabolism might start earlier, but the authors said data for ages 40 to 60 were too sparse to be sure.

Does menopause slow your metabolism?

The research here does not show that directly. The 2019 SWAN study found faster fat gain and lean mass loss around the menopause transition, but it measured body composition rather than energy expenditure, and weight gain did not measurably accelerate. It is observational, so it shows association, not cause.

Can you speed up your metabolism?

Only slightly, and with uncertainty. A 2020 meta-analysis found resistance exercise raised resting metabolic rate by about 96 kcal a day, while aerobic and combined exercise had no significant effect. The authors noted high risk of bias, so strength training is better valued for muscle and function.

Does poor sleep slow your metabolism?

Not clearly. A 2017 meta-analysis found that partial sleep deprivation did not significantly change total energy expenditure or resting metabolic rate, but did increase energy intake by about 385 kcal. The pooled analysis was small, with 11 studies and 172 people, so read it cautiously.

Can a fitness tracker show my metabolism?

No, not reliably. The 2021 study used doubly labelled water, a laboratory method over one to two weeks, which wrist devices do not replicate. A tracker can show steps, activity and sleep trends over months, which helps you see habits, but it should not be used to judge your metabolism.

Final thoughts

Here is the short recap.

• In the largest measurement study to date, size-adjusted energy expenditure was stable from about 20 to 60, so a sharp drop in your 40s is not supported.
• Muscle, sleep and hormones do change in midlife, and they may matter more for weight and energy than metabolism itself.
• Strength training and regular movement are worth doing for health, but they are not a reliable metabolism boost; see a clinician for unexplained changes.

Your turn: What have you noticed change in your 40s, and what has helped? Tell us in the comments.

Sources and further reading

1. Pontzer H, Yamada Y, Sagayama H, et al., IAEA DLW Database Consortium. Daily energy expenditure through the human life course. Science, 2021.
2. Greendale GA, Sternfeld B, Huang M, et al. Changes in body composition and weight during the menopause transition. JCI Insight, 2019.
3. Al Khatib HK, Harding SV, Darzi J, Pot GK. The effects of partial sleep deprivation on energy balance: a systematic review and meta-analysis. European Journal of Clinical Nutrition, 2017.
4. Mitchell WK, Williams J, Atherton P, Larvin M, Lund J, Narici M. Sarcopenia, dynapenia, and the impact of advancing age on human skeletal muscle size and strength; a quantitative review. Frontiers in Physiology, 2012.
5. MacKenzie-Shalders K, Kelly JT, So D, Coffey VG, Byrne NM. The effect of exercise interventions on resting metabolic rate: a systematic review and meta-analysis. Journal of Sports Sciences, 2020.
6. NHS. Underactive thyroid (hypothyroidism). nhs.uk, accessed 2026.
7. NHS. Physical activity guidelines for adults aged 19 to 64. nhs.uk, accessed 2026.