What is ‘resting metabolism’ and how can we affect it?

What on earth is resting metabolism?

Resting metabolism, also known as resting metabolic rate or RMR for short, is the basic amount of energy you’ll expend in a day, just to maintain the body’s basic function.

I.e. The stuff that needs to happen to keep you alive.

We can use this figure, along with your activity energy expenditure and your dietary-induced thermogenesis to calculate your total daily energy expenditure.

I know what you may be thinking:

“Sounds complicated. Why would we want to know that?”

By using your RMR and daily energy expenditure, we can deliver far more accurate and effective nutritional advice.

Because while it’s not quite as simple as just working out ‘calories in vs. calories out’, this does have a significant bearing on how your body composition changes.


What dictates RMR?

A few things, actually.

Body composition is the largest factor in your RMR.

Active tissues, such as muscle and bone, need energy while at rest to maintain structure and form.

Fat, on the other hand, uses little to no energy at rest.

This means the leaner or more muscular someone is, the greater their resting metabolism – and we know that fat-free mass accounts for approximately 70% of RMR.

There are other factors at play, however.

Genetic factors, thyroid function, protein turnover, liver activity and adrenaline production all influence the RMR figure.


Can we affect our RMR?

When it comes to achieving your health and fitness goals, there are a few factors we can influence – such as calories consumed or amount of exercise.

But if we were able to raise your RMR, this would lead to an increased energy expenditure each day – independent of needing an increase in activity levels – which would help maintain a positive body composition.

The problem with the popular discussion amongst many coaches and trainers around raising metabolic rate is there’s historically been no clear information on what can raise it chronically, and to what extent.

But you know us, we’re only interested in research-based fact, not hearsay.

Fortunately, a recent study published in the Journal of Sports Sciences (Mackenzie-Shalders et al, 2020) has looked to summarise the existing data and answer the question with more clarity.

After reviewing 1,669 studies that discussed and investigated metabolism in some form, 18 were deemed to be of high enough value and validity to be studied further.

These studies looked at the effect of exercise regimes – both aerobic and resistance-based – on RMR, independent of any health outcomes.

The pooled study data showed that, on average, RMR increased by 74 kcal per day after an exercise programme.

Bad news though:

Given the wide range in data, this finding was not deemed ‘statistically significant’, meaning we can’t confirm it’s a true increase.

There was good news, however:

When the study looked at exercise regimes separately – and looked at the results of aerobic vs. resistance-based exercise – the findings were more interesting.

They found that while aerobic exercise didn’t have a significant impact on RMR, resistance exercise did. In fact it led to an increase of over 96 kcal per day – the equivalent of 2 ginger nut biscuits or a banana.

The likely reason being resistance based training is more anabolic or ’tissue-building’, meaning most individuals will develop more active tissue which, as we know, expends more energy when at rest.


What does this mean in real terms?

I’m aware that today’s Sciencecast has been a touch more ‘jargon-heavy’ than previous editions, so what do these findings actually mean?

Firstly, in addition to acutely improving our levels of physical activity, we can look to chronically develop our RMR, meaning we can maintain optimal body composition and maximise our health.

Secondly, while we know the exact impact, we know that resistance based training is most effective for developing RMR, so should be a key part of your exercise programme. And since It’s likely that it’s the muscle-building component of this style of training has the biggest effect, progressive overload is key to achieving your results.

That’s not to say that aerobic training doesn’t have any health benefits, but it has no real positive impact on your RMR.

But remember, while exercise is beneficial for creating a calorie deficit, diet and nutrition are the most effective.

You can’t outrun a bad diet!