A lemon, which some people falsely believe will speed up their metabolism.
Fitness Tip

This one thing can boost your metabolism


What leaps to mind when we say the word ‘metabolism’?

Is it that magic thing your friend has that means she can eat anything she wants? Is it why you won’t eat anything after 8 pm?

A lot of what we THINK we know about metabolism is wrong, and that’s partly because there’s a lot of myths (and marketing) getting around. Viral social media posts declare chilli peppers, green tea and coffee will speed it up! A friend told you that eating late at night will slow it down! Powders and pills in the ‘vitamin’ aisle claim to boost it. Models tell interviewers that drinking lemon water with pepper is what kickstarts theirs for the day.

With such an overwhelming amount of information, often from dubious sources, we decided it is time to take a deep dive into the science of metabolism. So before you make the switch to an all chilli-tea-lemon diet (seriously, don’t do that), read on to learn the basics, bust some myths and learn what really affects your metabolism.

What is your metabolism?

Metabolism is the process by which your body converts what you eat and drink into energy. Even when you’re lying in bed reading a book, your body is using energy to circulate blood, operate your digestive system, and so on – this expenditure is known as your resting metabolic rate.

Metabolism speed (how quickly your body burns up calories for energy) does vary from person to person. But what controls metabolism – i.e. why you might gain weight when your similarly aged and sized friend doesn’t – remains mostly a mystery.

Does building muscle speed up your metabolism?

Yes, it can, by a small amount (yay!), but more for men (boo). In a study of men and women who used strength training to increase lean muscle mass by an average of 2kg over 24 weeks, the men increased their overall resting metabolic rate by about 600kj (140 calories) per day, while the women experienced an overall increase of about 196kj (47 calories).

Emily Skye holds a 5kg dumbbell in one hand.

Yep, building muscle can boost your metabolism. Turns out Emily is right – weights really ARE your mates.

Simply put, the women had ‘sped up’ their metabolisms by, on average, enough to burn the equivalent of one small apple (or a square of dark chocolate, if you prefer) per day. It might not seem like a lot, but according to Lisa, it all adds up.

“If you can burn an extra 47 calories per day, that’s over 300 calories per week. Over time, that’s significant! Gaining muscle is one of the only evidence-based ways of boosting metabolism.”

Plus, from your workout performance to your bone health, strength training delivers plenty of benefits beyond that.

Will cutting calories slow your metabolism?

This one is not so much down to the cutting of calories, but the reduction in weight that can result from it. Smaller people don’t need to expend as much energy to function – so if your weight drops, your resting metabolic rate will likely drop too.

However, what happens to metabolism after losing a significant amount of weight is complex.

A study of former Biggest Loser contestants – almost all of whom put weight back on after the show ended – revealed that their resting metabolic rate was slower than other people of similar size who had NOT lost weight. Basically:

  • contestants lost weight, and their metabolic rate slowed

  • they regained weight, but their metabolic rate remained at the lower speed.

A smoothie served in a glass with froth and powdered cocoa on top.

Our Peanut Butter Cup Power Smoothie is the perfect post-workout protein hit to aid muscle recovery.

This is called adaptive thermogenesis, or metabolism adaptation, but you might know it by its scary and not-quite-accurate nickname ‘starvation mode’.

Lisa points out that this metabolic adaptation can be partly explained by the rapid muscle loss that accompanies an extreme crash diet and exercise program – the kind the participants on the reality show followed, for example.

“When someone is shifting weight that quickly, it’s impossible to lose just fat. They lose muscle as well, which reduces metabolic activity,” she says.

Happily, there is a growing consensus that metabolic slowing occurs when you’re actively losing fat by burning more than you eat, which means that once you’ve reached your goal, upped your food intake and started building muscle, your metabolism will likely return to ‘normal’.

Can certain foods or drinks speed up your metabolism?

In a word, no. While some products may be touted as the key to speeding up your resting metabolism (so you’ll burn fat while doing nothing at all!), experts point out that you’d be fighting your own biology to do it. For example, if you have a bigger liver or brain than someone else, you’ll naturally use more energy.

And what about the rumour that spicy food will jumpstart your metabolism? Advanced Sports Dietitian Lisa Middleton says that while some research on capsaicin – the chemical in chillies – has shown a mild effect “it’s so small that it’s unlikely to have any impact on fat burn.”

Emily Skye holds a lemon towards the camera, squeezing it with her hand.

Water with lemon might be a fresh way to start the day, but unfortunately it won’t speed up your metabolism.

Will ageing slow down your metabolism?

We’ve all heard of middle-aged spread, the supposedly unavoidable truth that we’re all going to gain weight because our metabolism slows down as we get older. But new research has blown that old belief out of the water, finding that metabolism actually stays steady from ages 20–60. It was also thought that the average woman had a slower metabolism than a man, but the research found that there is no significant difference when accounting for differences in height, weight and body fat.

Can calorie cycling speed up your metabolism?

Calorie cycling, sometimes called metabolic confusion, is a style of diet that alternates between days of lower-calorie and higher calorie intake. Proponents claim calorie cycling can ‘trick’ your body into avoiding adaptive thermogenesis.

So, does it work? One study found that calorie cycling did appear to offset adaptive thermogenesis, but more research is needed to deliver a solid verdict.

It’s important to keep in mind that calorie cycling can be complicated and may be unsustainable – especially if you’re training regularly. The cycle of restricting/increasing calories could also lead to binge eating and an unhealthy relationship with food – which is absolutely not what you need.

So what can I do about my metabolism?

When it comes to your metabolism, there is no magic bullet, but Lisa says that building and maintaining muscle is what you should focus on.

“Try to time your protein intake to promote optimal muscle recovery and development, which can certainly have an impact on metabolism and help you burn body fat,” Lisa says.

Your FIT planner outlines a sustainable approach to burning fat and sculpting your body. You don’t need to ‘trick’ your body or go hungry. Getting sustainable results is all about finding a balance of nourishing food and efficient exercise.

It may require some lifestyle change, but hey, that’s a whole lot easier than changing a bodily process that even the scientists don’t fully understand.

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