Why your metabolism changes as you age – and how to give it a boost

At one time or another, most of us have blamed our metabolism: either it’s so ‘fast’ that we can justify our decision to skip the healthy salad and tuck into chips and chocolate cake, or it’s so ‘slow’ that we only have to look at a biscuit to gain weight. Unsurprisingly, there’s a bit more to it than that. 

‘When we talk about metabolism, we’re referring to all the chemical processes that allow the body to convert food into energy, build and repair tissues, regulate hormones and maintain essential functions,’ explains Dr Richard Mackenzie.

Put simply, your metabolic rate is the amount of energy – or calories – that your body uses in a set period of time. However, Dr Mackenzie believes it’s vital to consider the bigger picture. ‘Many discussions of metabolism focus only on how many calories are burned. 

'A broader and more useful perspective is to think about metabolism as involving both energy expenditure and metabolic health, which means how effectively the body processes and responds to nutrients.’

Our expert

Dr Richard Mackenzie has over 30 years’ experience helping people improve their metabolic health. Based at The Metabolic Health Clinic in London’s Harley Street, he is also a leading biomedical researcher and the author of How Stress Works.

Our expert

Dr Jack Mosley is the son of Dr Michael Mosley, pioneer of the 5:2 diet and the Fast 800 programme. He has worked as a doctor in emergency medicine in the UK and Australia and now works as a GP registrar. He is the author of Food Noise.

What you need to know about your metabolism – at a glance

• ‘Metabolism’ refers to the processes that convert the food we eat into energy. 
• Your metabolism doesn’t slow down significantly until after the age of 60; even then, it’s mainly your lifestyle habits that influence how many calories you burn. 
• Your thyroid and hormones such as insulin play key roles in regulating metabolism. 
• Fluctuating hormone levels around perimenopause and menopause can lead to weight gain, even if you haven’t changed what you eat.  
• Unexplained weight gain and increased fat storage around the waist can be signs of impaired metabolic health. 
• Boosting your muscle mass increases the amount of energy you burn, even while you sleep.
• You can support a healthy metabolism by staying active, eating well, getting enough sleep and managing your stress levels. 
• A poor diet, excessive snacking and reliance on processed foods can all damage your metabolic health. 

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How do hormones influence metabolism?

The key hormone involved in metabolism is insulin, which is produced by the pancreas and helps move glucose from the bloodstream into the cells. 

If cells become less sensitive to insulin, known as insulin resistance, this process becomes less efficient and results in increased fat storage, especially around the waist, along with an increased risk of metabolic syndrome: a cluster of conditions including high blood pressure, unhealthy cholesterol levels (for example, high triglycerides or low ‘good’ HDL cholesterol), abdominal obesity and raised blood sugar. 

Over time, metabolic syndrome can increase the risk of type 2 diabetes, heart attack and stroke. 

Fluctuating hormone levels during perimenopause and menopause can also affect your metabolism. ‘Declining oestrogen levels can promote fat storage, especially around the waist. Muscle mass may decrease more rapidly and insulin sensitivity may worsen. Weight gain is common, even without major changes in calorie intake,’ says Dr Mackenzie. 

However, research indicates that hormone therapy (HRT) may improve insulin sensitivity and help reduce the increase in abdominal fat associated with menopause, although it isn't recommended as a weight-loss treatment. 

Thyroid hormones also play a part. Hypothyroidism (low levels of thyroid hormones) can slow down the metabolism, leading to weight gain, while hyperthyroidism (high levels) can speed it up, leading to weight loss. Both conditions can be diagnosed with a simple blood test, and treated with medication. 

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Does your metabolism inevitably slow down with age?

Even if you can no longer get away with eating the way you did as a teenager, this isn’t simply a result of your formerly fast metabolism slowing down. Research shows that our metabolic rate actually remains fairly stable until around the age of 60, at which point our energy expenditure tends to decline more quickly. Even then, research shows that it only decreases by an average of 0.7% each year. 

‘The most noticeable metabolic shifts for many people occur in their 40s and 50s, due to changes in body composition, insulin sensitivity and the hormonal changes associated with menopause,’ says Dr Mackenzie. 

According to Dr Mackenzie, the term ‘slow metabolism’ can be misleading: ‘Your metabolism doesn’t typically fall off a cliff in middle age. For many adults, the feeling that their ‘metabolism has slowed’ may reflect increasing insulin resistance and changes in body composition more than a major decline in calorie-burning rate alone.’

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Is age-related weight gain primarily metabolic or lifestyle-driven?

Although many of us gain weight as we age, it certainly isn’t inevitable – more often than not it’s our lifestyle to blame. 

‘Regular movement remains one of the most effective ways to support metabolic health. Exercise helps maintain insulin sensitivity, supports glucose control, and preserves muscle mass,’ says Dr Mackenzie. Muscle is metabolically active tissue, which requires constant energy, even when you’re sleeping. It burns more calories than fat, so it also reduces the risk of obesity. This is why strength and resistance training, not just cardio, is associated with better metabolic health.' 

Along with physical inactivity, there’s also evidence that prolonged stress and poor sleep can impair insulin sensitivity. Stress increases levels of the hormone cortisol, reducing insulin sensitivity and encouraging abdominal fat storage; poor sleep disrupts appetite, impairs blood sugar control and encourages inactivity, all of which lead to weight gain.  

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Can you boost your metabolism?

We all love the idea of a quick fix, but Dr Mackenzie says there’s no magic way to boost your metabolism. 

‘There’s no evidence-based shortcut that dramatically increases metabolic rate long term. Many products and diets claim to ‘boost metabolism’, but the effects are usually very small and temporary. Things like caffeine, green tea extract and spicy foods may slightly increase calorie burning, but not enough to produce substantial weight loss on their own. 

'Rather than trying to ‘speed up’ metabolism, the focus should be on preserving muscle, staying active and improving insulin sensitivity. Healthy metabolism is built through long-term habits, not high-protein products or metabolism-boosting claims.’

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With this in mind, Dr Mackenzie recommends the following six strategies:

1. Stay active Regular movement increases calorie burn – simply standing more can help. Strength training helps to prevent muscle loss, which begins around the age of 30, when we naturally lose up to 8% of our muscle mass per decade. This process accelerates after the age of 60, but exercise is the best way to combat it. 
2. Eat enough protein Without adequate protein, our bodies can’t build and maintain muscle effectively. The NHS recommends a baseline of 0.75g per kilo of bodyweight per day, but you may need more if you’re building muscle or exercising regularly. 
3. Focus on quality foods Limit highly processed foods high in salt, sugar and saturated fat, where possible, and prioritise wholegrain, fibre-rich foods and healthy fats. 
4. Protect your sleep Dr Mackenzie says sleep is one of the most ‘under-appreciated pillars’ of metabolic health. Try to follow a consistent sleep schedule, keep your bedroom cool and comfortable, and make time to wind down before bed. 
5. Manage stress Chronic stress can influence appetite, blood sugar control and fat distribution. Yes, it’s easier said than done, but make time to disconnect, practise breathing techniques and seek expert help if your stress feels unmanageable. 
6. Maintain a healthy weight This lowers your risk of metabolic disease, which has a more long-term impact than simply trying to ‘boost’ your metabolism.

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3 habits that can harm your metabolism

There might not be any shortcuts to a faster metabolism, but Dr Mosley says these everyday habits could be working against you. 

• Late dinners ‘Eating a large meal after 9pm or snacking late at night – or during the night if you’re a shift worker – can affect your metabolism. Your liver, gut and pancreas all have their own clocks in the same way the brain does and don’t work as well in the early hours.’
• Snacking 'Some research suggests constant snacking can impair your body’s metabolic flexibility, which is its ability to switch between burning glucose from food and stored body fat. This leads to energy crashes and persistent hunger. ‘Snacking excessively, especially on ultra-processed foods (UPFs), is likely to lead to weight gain, even if it doesn’t directly slow your metabolism.’ 
• Poor diet ‘The microbes in your gut play an important role in digestion. Emerging evidence suggests that your gut microbiome may play a role in how effectively calories are extracted, as well as blood glucose control.’

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What are the signs that my metabolism is changing?

Dr Mackenzie advises that the following symptoms could indicate poor metabolic health:

• Increasing waist circumference. For most men, less than 94cm/37 inches is low risk; for most women, less than 80cm/31.5 inches is low risk. 
• Unexplained weight gain or difficulty losing weight. 
• Fatigue, particularly after meals. 
• Energy crashes throughout the day. 
• Elevated blood pressure. 
• Rising cholesterol or triglyceride levels. 
• A family history of type 2 diabetes or cardiovascular disease.

Your GP can check your thyroid function and blood glucose, and may recommend other blood tests where appropriate. 

‘If you have risk factors or concerns, seeing your GP is likely to be more informative than chasing metabolism-boosting products or relying on symptoms alone,’ recommends Dr Mackenzie. 

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