Metabolism after 40: what actually changes

Probably not. The idea that your metabolism crashes at 40 is not what the data show. A 2021 study published in Science measured total daily energy expenditure in men and women from 8 days to 95 years old and found that, once adjusted for fat-free mass, expenditure stays stable right through adulthood — from 20 to 60 — and only then begins to decline. There is no drop at 40. There is a slow, continuous slide across decades, and a more visible one later in life.

If you feel you put on weight more easily than you did at 25, it is worth looking at what has changed since then. The likeliest explanation, though, is not a metabolism that switched off on your fortieth birthday. Energy expenditure adjusted for fat-free mass holds steady through adulthood, between 20 and 60, and only then falls.

So what actually changes around 40?

What the evidence describes is a curve, not a step. Energy expenditure adjusted for fat-free mass climbs steeply in the first months of life, falls until it settles somewhere around the age of 20, and stays there. Through adulthood, that stability is the observed pattern.

From 60 onwards, yes, adjusted energy expenditure starts to fall. Which means worrying about your metabolism makes more sense as something you look at over time than as a dated event. It also means that, at 40, the thing the available evidence does not support is the idea of a slowdown at that age.

One more thing the evidence does not support: that there is a point at which your body slows down because of age and nothing can be done about it. That has not been shown. What has been shown is that fat-free mass tracks energy expenditure across adult life, and that physical activity is part of the health recommendations for adults.

And at 50? Same question, similar answer

Worth separating the two.

At 50, the available evidence still does not show an abrupt fall linked to age alone. What you have is the continuation of that stability described up to 60. The role of the menopause is a fair question — and one where the evidence is thinner. A 2020 meta-analysis on resting metabolic rate explicitly excluded people aged 65 or over and postmenopausal women. In other words, its results do not directly describe that group. On the basis of this body of evidence, we do not know what the menopause does to resting metabolic rate. Saying otherwise would be inventing it.

There is one exception that deserves saying out loud. If tiredness and weight gain arrived together and recently, and they seem out of proportion to what you eat and how much you move, it may be worth talking to your doctor. The NHS describes hypothyroidism as a common condition in which the thyroid does not produce enough hormones, which can cause symptoms such as tiredness and weight gain, and advises seeing a doctor if you suspect it. It is diagnosed with blood tests and it is treated. None of this is meant to alarm you, or to suggest it is your case — it is simply a possibility that will not be resolved by willpower, and one that does not belong in an article.

What the evidence says about exercise and metabolism — and where it gets shaky

Here things become interesting, and less tidy than the internet suggests.

A 2020 systematic review and meta-analysis pooling 18 studies looked at the effect of exercise on resting metabolic rate. Aerobic exercise combined with resistance did not significantly raise it. Aerobic exercise on its own had no significant effect either. Resistance training, though, did raise it compared with control groups. The authors themselves flag heterogeneous methods across the studies and a high risk of bias in the work included.

Put without the enthusiasm: there are signs that strength training may have some effect on resting metabolic rate, but it is not a solid conclusion. We do not yet know whether that effect holds over the long term, or how large it is in the real life of a 45-year-old. Any article promising to "speed up your metabolism" with a specific workout is going beyond what is known.

What is not shaky is the activity recommendation itself. The NHS advises adults aged 19 to 64 to do strengthening activities covering all major muscle groups on at least 2 days a week, plus at least 150 minutes of moderate activity or 75 minutes of vigorous activity a week, and to cut down the time spent sitting or lying down. That is not a metabolic promise. It is the baseline, and it is refreshingly concrete.

If you have not exercised for a while, or you have health conditions or medical concerns, the NHS advises speaking to your GP first, so that the activity and its intensity suit your situation.

The practical part: routine, timing, forgetting and cost

At 40 and at 50, the obstacle is rarely not knowing what to do. It is fitting it in. Which is where being concrete beats being motivational.

Strength before cardio, if you have to choose. Not because it will speed up your metabolism in any guaranteed way — we do not know that — but because it is what the NHS explicitly recommends. Two sessions a week, in the calendar like anything else that cannot be moved.

Against sitting, the trick is making it inconvenient. Getting up every hour needs no app. It needs a reason: the glass of water left in the kitchen rather than at the desk, the printer further away, the phone call taken standing up. Small frictions you have planned in advance work better than willpower.

On forgetting: if your week has two strength sessions and one long walk, that is a routine. If it has twelve planned sessions and you did two, the problem is not discipline — it is the plan. Cut it back to what you can keep up in a bad month, not a good one.

Cost: strength training does not require a gym. It requires progressive load, and you can get that with body weight, a resistance band or a simple pair of dumbbells. The real expense is often in starting and stopping three times, not in the membership.

Where a supplement fits — and where it does not

This is the part where we would rather disappoint you than be agreeable. The evidence we have does not allow any claim that a supplement speeds up your metabolism, raises energy expenditure or makes up for what your routine does not do. If you are looking for something to replace the two strength sessions a week, it does not exist — and any page telling you otherwise is selling you something else.

That said, there may be a narrow place for a supplement, and it is convenience, not metabolic effect. Active Metabolism Gummies are a food supplement in gummy form, for adults, with green tea extract, garcinia, raspberry ketone and green tea seed among the ingredients. The stated serving is 2 gummies a day, and the maximum daily dose is 2 gummies, chewed after a meal. The product is not intended for pregnant or breastfeeding women or for anyone under 18. It should not be taken on an empty stomach, or by anyone consuming other products containing green tea on the same day, and you should not consume a daily amount equal to or greater than 800 mg of EGCG. If you are ill, especially with liver disease, or you take medication, speak to a healthcare professional before use. It contains polyols; excessive consumption may have a laxative effect.

Notice what is not written above: any promise. If you are looking for a supplement because you want an intervention that does the work for you, this is not that path. If you are looking because your routine is already in place and you want something simple to slot in, read the label carefully and check for yourself what is in it — we are not going to give you numbers that are not in the information we hold.

What belongs to your doctor and not to this article

Some decisions an article should not make for you, and it is worth being explicit about which.

• If you suspect hypothyroidism — persistent tiredness and weight gain with no clear explanation — speak to your doctor. It is diagnosed with blood tests and it has a treatment.
• If you have a health condition, liver disease, or take regular medication, check with a healthcare professional before starting any supplement, including those containing green tea.
• If you have not exercised for a while, or you have cardiovascular or musculoskeletal concerns, ask for guidance before increasing intensity.
• If you are pregnant or breastfeeding, no supplement of this kind is intended for you — and that conversation is with whoever is looking after you, not with a shop.

None of this is box-ticking. It is the difference between acting with information and acting with hope.

What to do this week, without buying anything

Start with one thing only. Put two strengthening sessions in next week's diary — not seven, two — and treat them as commitments that do not move. Then count honestly how many hours of your day you spend sitting. You do not need to change everything; you need to know the starting point.

If your tiredness and your weight feel out of proportion to what you do, book an appointment. If they feel proportionate to a routine that has changed over the past ten years, then you already know where the work is — and the available evidence does not allow you to blame your metabolism. The evidence on what age does to energy expenditure is reasonably clear for adulthood, murkier after 60, and murkier still on the role of the menopause. Where the evidence is murky, the best we can do is say so and act on what is within reach. At 40, that is quite a lot.