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4 reasons your metabolism slows down as you age

There is a commonly held belief that your metabolism automatically slows down as you age. But is this the case? If so, what are the causes?

There is a commonly held belief that your metabolism automatically slows down as you age. But is this the case? If so, what are the causes? 

Let’s look at what your metabolism is, four reasons why your metabolism slows down as you age, whether your metabolism automatically slows down, and how to repair it in later life.

What is your metabolism?

Your metabolism is the sum of all of the chemical processes in your body that allow you to live. Your metabolism has three main components: 

  • Basal metabolic rate (BMR)
  • Thermic Effect of Feeding (TEF)
  • Physical Activity (PA)

Your BMR represents all the calories that your body burns just functioning. If you lay down in a darkened room with nothing to eat, your body would burn calories to fuel breathing and many other body processes. Your BMR represents around 60-75% of the calories you burn per day.

The thermic effect of feeding (TEF) represents the calories that your body burns while eating, digesting, and excreting food. If you've ever gotten sweaty after eating a substantial meal, then you will have seen this process in action. TEF represents around 10% of the calories you burn per day.

Physical activity involves structured exercise (going to the gym, doing push-ups at home, going for a jog), and non-exercise activities. These can include walking the dog, or running for a bus; any physical activity you wouldn't necessarily class as exercise. Physical activity represents around 15-30% of total calories burned per day.

So why the science lesson?

Because you must understand that your metabolism isn’t a thing, it’s just a description of all of the calories your body burns each day performing chemical processes. 

People talk about their metabolism slowing in like they talk about their muscles aching or breaking their arm. 

But actually, your metabolism is mostly controlled by the actions you take. 

That said, the ageing process can lead to a slower - or lowered - metabolism in several ways.

Four reasons why your metabolism slows down as you age

If you look at the three parts of your metabolism (BMR, TEF, and PA), you can see how two are within your control, while one (BMR) is not. 

Your BMR can be affected by many things, and as you age, your BMR can begin to decrease. But the other two components are also often affected by ageing. Here are four reasons why your metabolism slows down.

Reason #1: You move less

Physical activity represents 10% of your calories burned per day. But that’s an average. If you increased your physical activity, you could increase your calories burned, and alter that percentage. That’s why exercise increases your metabolism and can help lead to weight loss.

But as we age, we tend to move less. There are several reasons for this. Our bones become weaker, our muscles become smaller, and we can become frailer as a result. This happens to everyone eventually.

This means that most people tend to exercise less, you don't see too many 60-year-olds performing the high jump, or the 200m sprint (though some still do). The type of activity you perform changes and begins to reflect the limitations of age.

When you hit your 90s even a walk around the nearby park may feel like a Herculean task compared to how it felt 60 years ago. Less movement means a decreased metabolism.

Reason #2: You lose muscle mass

One of the reasons you become frailer as you age is that you begin to lose muscle mass. Partly, this is because you are moving less. It's also partly due to diet, sex hormones, and age-related issues.

As we now know, losing muscle can lead to less physical activity, which creates a vicious cycle. But losing muscle can affect your basal metabolic rate (BMR). This is because muscle tissue requires a lot of energy to maintain. That’s why men have higher metabolisms than women, on average; because they have more muscle mass.

It’s also why bodybuilders can eat so much food without gaining weight. Their metabolisms are through the roof! Once you begin to lose muscle mass, your metabolism will start to drop.

Reason #3: You eat less

While this does not affect everyone, many people experience a loss of appetite as they age. According to a study, between 15% and 30% of older people are estimated to have anorexia of ageing.

This can have many health implications and explains why older people are often most at risk of malnutrition, even in developed countries.

But eating less can have a profound effect on your metabolism. Not only does it mean you burn fewer calories due to the thermic effect of feeding (TEF), it can also accelerate the loss of muscle mass and lead to a reduction in physical activity.

Reason #4: Your body produces fewer sex hormones

We know women go through the menopause. While the "male menopause" doesn’t really exist, men do see a considerable drop off in testosterone production as they age. A decrease in oestrogen for women or testosterone for men will reduce the basal metabolic rate.

Lowered oestrogen and testosterone can also make it challenging to build and maintain muscle, possibly affecting physical activity, too.

Your metabolism may vary

Everyone is different, and we all probably know (or have known) a person in their 90s who is more active than most 30-year-olds. Some men don't appear to lose half as much testosterone as others. If they lead a more active lifestyle, they may maintain more muscle and have a higher metabolism. 

What scientists have noticed is that being more active in your 30s to 60s can have a significant knock-on effect in later life. Still, it's never too late to make changes that can improve matters.

How to repair your metabolism in later life

Your metabolism at 60 is not likely to be anywhere near as high as it was at 20. However, it is still possible to get that "metabolic age" down.

Here are five steps that you can follow to improve your metabolism:

  1. Eat more protein – Due to not absorbing leucine, you’ll need more protein to see the same benefits.
  2. Get to the Gym – Lifting weights will improve your cardiovascular fitness, and help you build and maintain more muscle, which will keep your metabolism raised. 
  3. Walk more – Aim for 6,000 steps per day, or 5,000 if you also do a workout.
  4. Join a sports team – Walking football, bowls, karate, whatever you fancy.
  5. Sleep 8 hours per night – Improved sleep can help with sex hormone production, repair from exercise, and help you be more active during the day.

Hopefully, you have a better understanding of what your metabolism is, why it can decrease with age, and how to counteract this as best you can.

Matt Smith

Matt Smith

Matt Smith is a fitness and nutrition writer who runs the website Beer n Biceps. He has a degree in Sports Science and was a personal trainer in London for several years.