Last reviewed: October 2026
“I’m eating the same and doing the same, but my body is changing.” It is one of the most common things people say in their 40s and 50s. It is not in your head, and it is not a lack of willpower. Several things change in midlife at once.
It’s not just “a slowing metabolism”
You may have heard that metabolism crashes at 40. A large 2021 study in the journal Science, which measured the daily energy use of over 6,000 people, found that once you allow for body size and muscle, metabolism stays fairly steady from about age 20 to 60, then slowly declines. Evidence: strong for this overall pattern.
So what is going on? Mostly, changes in body composition (how much muscle versus fat you carry), where fat is stored, sleep, and how your body handles sugar.
1. Hormones and where fat is stored
For women, the menopause transition changes where fat goes more than how much you weigh. A long-running US study (SWAN) found that as the menopause transition began, the rate of fat gain doubled while muscle (lean mass) started to decline. These changes continued until about two years after the final period, then levelled off. Interestingly, total weight on the scales kept rising at about the same steady rate. The change was in what that weight was made of. Evidence: strong (large long-term study).
Lower oestrogen is also linked with more fat being stored around the tummy rather than the hips and thighs. Evidence: moderate.
For men, testosterone levels tend to fall gradually with age, but in midlife the bigger driver is usually the reverse: carrying extra weight, particularly around the middle, tends to lower testosterone.
2. Losing muscle
From around our 30s and 40s, most people slowly lose muscle unless they actively work to keep it. Muscle helps with strength, balance, blood sugar control and everyday energy use. Less muscle and more fat can mean your clothes fit differently even if the scales do not move much. Evidence: strong.
3. Visceral fat: the fat you can’t see
Fat stored deep inside the belly, around the organs, is called visceral fat. A higher waist measurement is a rough sign of it. Visceral fat is more strongly linked with type 2 diabetes, heart disease and fatty liver than fat elsewhere in the body. Studies have found visceral fat increases across the menopause transition. Evidence: strong for health links; moderate for the exact size of the menopause effect.
4. Insulin resistance
Insulin is the hormone that moves sugar from your blood into your cells. With less muscle, more visceral fat, poor sleep and less activity, the body can become less responsive to insulin. This is called insulin resistance, and it can make weight gain around the middle more likely and raise the risk of type 2 diabetes. Evidence: strong.
5. Sleep
Midlife sleep is often disrupted by night sweats, stress, caring responsibilities, snoring or sleep apnoea. Short sleep is linked with weight gain. In small laboratory studies, cutting sleep short changed appetite hormones, increasing hunger. Evidence: moderate for the link; small studies for the hormone effects.
What helps
There is no single fix, and it is reasonable to expect gradual change rather than fast results. These approaches have the best support.
Resistance (strength) training. Lifting weights, using resistance bands or bodyweight exercises such as squats and push-ups two to three times a week helps you hold on to, or build, muscle at any age. Evidence: strong. It does not have to mean a gym.
Enough protein. Protein helps your muscles respond to training, and it helps you feel full. Including a source of protein at each meal, such as eggs, fish, meat, dairy, tofu, beans or lentils, is a practical approach. A large review found protein added to resistance training gave a modest boost to muscle and strength gains. Evidence: moderate. People with kidney disease should check with their practitioner first.
Regular movement. Walking and other activity help with heart health, blood sugar, mood and sleep, even when the scales do not change much. Evidence: strong.
Prioritising sleep. A regular bedtime, a cool dark room, limiting alcohol and caffeine later in the day, and getting help for night sweats or snoring all count. If you snore loudly or wake unrefreshed, ask about sleep apnoea. Evidence: moderate.
Looking at more than the scales. Waist measurement, strength, energy, blood pressure and blood tests such as sugar and cholesterol often tell you more about your health than weight alone.
Medical treatments may be part of a plan for some people, but they work best alongside these foundations, and they are not right for everyone. Menopausal hormone therapy is not a weight-loss treatment. Your practitioner can talk through what is appropriate for you.
Be kind to yourself
Midlife body changes are common and largely driven by biology, not failure. Small, steady changes in strength, food, sleep and movement add up, and they bring health benefits even if the number on the scales changes slowly.
References
- Pontzer H, Yamada Y, Sagayama H, et al. Daily energy expenditure through the human life course. Science. 2021;373(6556):808–812. https://doi.org/10.1126/science.abe5017
- Greendale GA, Sternfeld B, Huang M, et al. Changes in body composition and weight during the menopause transition. JCI Insight. 2019;4(5):e124865. https://doi.org/10.1172/jci.insight.124865
- Lovejoy JC, Champagne CM, de Jonge L, Xie H, Smith SR. Increased visceral fat and decreased energy expenditure during the menopausal transition. International Journal of Obesity. 2008;32(6):949–958. https://doi.org/10.1038/ijo.2008.25
- Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine. 2018;52(6):376–384. https://doi.org/10.1136/bjsports-2017-097608
- Spiegel K, Tasali E, Penev P, Van Cauter E. Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Annals of Internal Medicine. 2004;141(11):846–850. https://doi.org/10.7326/0003-4819-141-11-200412070-00008
This article is general information only and is not a substitute for individual medical advice. Talk to your health practitioner about your own situation.