Thinking Nutrition

Can you really ‘boost your metabolism’?

August 17, 2021 Dr Tim Crowe Episode 78
Thinking Nutrition
Can you really ‘boost your metabolism’?
Show Notes Transcript

All manner of diet and exercise hacks are claimed to ‘boost your metabolism’, but what, if anything are they really doing to your body? In this podcast, I’ll explain what exactly is meant when you hear the term ‘metabolism boosting’, the factors that you can and can’t control that alter your metabolism and explore how much we can really blame our metabolism on weight changes.

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All manner of diet and exercise hacks are claimed to ‘boost your metabolism’, but what, if anything are they really doing to your body? In this podcast, I’ll explain what exactly is meant when you hear the term ‘metabolism boosting’, the factors that you can and can’t control that alter your metabolism and explore how much we can really blame our metabolism on weight changes. 

To start off, let’s consider the term ‘metabolism’. It means the process by which the body converts food into energy to both sustain life and to support physical activity, whether it’s dedicated exercise or non-exercise activity just helping us move around. The main internal metabolic processes include breathing, digesting food, transporting nutrients to the cells through the blood, use of energy by your muscles, nerves, and cells, and elimination of waste products from your body.

So, that’s all you need to know about what actually biochemical metabolism is. Because a much more relevant term – and this is what most people mean when they talk about metabolism – is basal metabolic rate. This is the energy (measured in kilojoules or calories) a person expends over the course of a day just to keep the body functioning. Maintaining body temperature, breathing, blood circulation and repairing cells are all essential requirements for a functioning body. These processes are always happening and use a lot of energy.

Your basal metabolic rate is the most significant component of your total metabolic rate, accounting for about two-thirds of the total calories expended daily for the average person. Of course, that percentage of BMR will drop the more active a person is, but it is still a large number.

BMR is slowest when a person is sleeping, but it is usually measured in a room with a comfortable temperature when the person is awake and lying still after a restful sleep and an overnight fast. A similar measure of energy output – called the resting metabolic rate (RMR) – is slightly higher than the BMR because its criteria for recent food intake and physical activity are not as strict.

Everyone's metabolic rate is different, as many factors can influence how fast (or slow) our body uses or converts energy. For the most part, the BMR is highest in people who are growing (such as children, adolescents and women who are pregnant) and those with considerable lean body mass such as physically fit people.

In general, the more a person weighs, the more total energy is expended on basal metabolism, but the amount of energy per kilogram of body weight may be lower. Let me explain: take for example the BMR of an adult which might be 6500 kilojoules per day and compare that to an infant’s which may be only 2000 kilojoules per day. But, when adjusted for body weight, the infant’s BMR could be twice as fast as the adult. Similarly, a normal-weight adult could have a metabolic rate one and a half times that of an obese adult when adjusted for bodyweight because lean tissue is metabolically more active than body fat.

There are a variety of online calculators that use different equations to estimate your BMR based on your age, sex and body weight. All of these are estimates only as an accurate BMR can only be measured by monitoring the amount of oxygen inhaled and carbon dioxide exhaled. For most people, it is utterly irrelevant to know what your BMR is. If your goal is weight changes, and your current diet and physical activity plans aren’t moving it, then you either need to eat less or move more – preferably, both.

Metabolism slows as we age. That’s because we gradually lose muscle mass with age which equates to a decrease in basal metabolic rate of approximately 1% to 2% per decade.

Your height also affects your metabolism. If two people weigh the same, the taller, thinner person will have the faster metabolic rate – reflecting the greater skin surface area through which heat is lost by radiation in proportion to the body’s volume.

Environmental temperature also affects metabolic rate. The body uses as much as 40 percent of its total energy expenditure in an attempt to keep its temperature stable. So, if you are exposed to extreme temperatures, your body will have to work harder to regulate your core temperature.

Health status and certain medical conditions can also influence metabolism. For example, one regulator of metabolism is the thyroid gland. If not enough thyroid hormone is made as is the case with hypothyroidism, metabolism may decrease and result in weight gain. Whereas, if the thyroid produces too much (which is called hyperthyroidism), this typically contributes to weight loss. Don’t get too excited or start wishing you could develop hyperthyroidism to help you lose weight – it is a nasty medical condition that also causes rapid heartbeat, anxiety, excessive sweating, insomnia, hair loss, diarrhoea and so the list goes on.

Having a fever can also affect a person’s basal metabolic rate. For each increase of half a degree Celsius in a person’s internal body temperature, their basal metabolic rate increases by approximately 7 percent.

So, for the big question: can you change your metabolism? Firstly, there are some things that you cannot change about your metabolism. For example, you can't change your age or sex. But there are some things that you can do that may change your metabolism. These include being more active either through exercise or just moving more throughout the day. Adding muscle through resistance training can also help to increase metabolism.

The problem though is that it’s very difficult to change your resting metabolic rate because you can’t change the number of calories that your brain needs or your heart needs or any other numerous internal processes that keep you alive.

And while your muscle mass does burn calories even when you’re not doing anything, it still only amounts to a small amount of the total resting metabolic rate. But there are lots of other good reasons to be active and keep your muscle mass growing, especially with advancing years.

So, can a “sluggish metabolism” be blamed for weight gain? Except for certain endocrine disorders such as hypothyroidism, the answer is a clear no. People who are overweight actually have higher resting metabolic rates on average than people of a lower body weight. As someone gains more weight from storing more fat, the body needs to support that excess mass to move it around. Imagine you had to live with a 20 kg weight tied around your waist. You would struggle to deal with this for the first few weeks, but over time you would build up extra muscle – especially in your legs – to help support it. Slow and insidious weight gain just gives more time for your body to adapt. And more muscle equals a higher metabolic rate at rest. Also, with an increase in body size, there is a change in internal organ size and fluid volume, which further increases the metabolic rate.

So, is it possible to speed up metabolism? There are many pills, supplements and foods that claim to boost metabolism and burn fat. Most of these claims are unproven. Some substances such as caffeine and chilli do have a small effect on metabolic rate, but not in supplement form, and the effect is very small.

It is true that some foods do take more energy to digest than others. It is called the thermic effect of food and it is the energy required to digest and assimilate food. It can differ depending on the macronutrient content of the meal with fat having an energy cost of about 5%, carbohydrates about 10% and protein around 25%. Before you get too excited about all of this, you can’t ‘eat yourself thin’. Think of the thermic effect of food as more of an energy tax on food, but most of the energy in the food you will still make use of. But there is some really interesting research to show that highly processed foods take less energy to digest than whole foods. Which is yet another way that eating too many of these types of foods will more easily lead to weight gain – we simply have more of the calories in them available to us as the body has less work to do in chewing, digesting and absorbing them

Rather than focusing on specific foods or supplements anyone hoping to ‘boost their metabolism’ should consider their diet and lifestyle as a whole. A diet rich in protein and minimally processed foods combined with regular activity, with a focus on muscle building resistance exercise will definitely keep you healthier than any transient effects on your metabolism.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.