Let’s Talk About Metabolism, Fast and Slow


You’ve heard the claim (or perhaps you’ve made the claim) that a person’s weight comes down to having slow metabolism or fast metabolism. Is this really a thing and can we boost our metabolism to burn more calories?

What is metabolism?

We need to take a step back and understand what metabolism is. What it is not is the primary cause for being overweight.

Metabolism is the internal process by which your body converts the calories you consume into the fuel your body needs in order to breathe, circulate blood, grow and repair cells, and everything else it does to survive

Did you know you can find out if your metabolism is slow or fast by taking an at-home metabolic rate blood test? This is quick, and cheap. You don’t need a doctor’s referral and you will receive doctor review results and recommendations within 24 hours.

Complex chemical reactions, linked by metabolic pathways, are constantly taking place inside your body to keep your cells alive and healthy. Catabolism is the breakdown of nutrients – carbohydrates, proteins and dietary fats – to create energy. Anabolism uses that energy to build and develop the larger complex molecules needed for the growth and maintenance of our tissues and cells.

Your body burns energy, measured in kilojoules, in three ways.

Burning Calories 1: Basal Metabolic Rate

Your Basal Metabolic Rate (BMR) is your resting metabolism. This is the energy you burn when seemingly doing nothing, while behind the scenes every cell in your body is working hard to keep you functioning. 

Your BMR is the minimum energy your body needs to run smoothly. It is also the most energy used by your body (estimated at 50-80% of your daily energy use) and is the part you have no control over.

Burning Calories 2: Thermogenesis

The energy used to digest, absorb, metabolise and dispose of nutrients from the food we consume is known as the thermic effect of food or thermogenesis. This accounts for 5-10% of your energy use.

Some foods have a higher thermic effect, and this is where you can make small changes to your diet to boost your metabolism. For example, protein takes longer to digest and absorb than carbohydrates and fats and therefore uses more energy. Caffeine and green tea have been linked with burning more calories. And hot or spicy food such as chili peppers, cayenne pepper, horseradish, mustard and ginger are considered metabolism-boosting foods. 

Burning Calories 3: Physical Activity

The energy we use in physical activity varies depending on how much we move during a day. This includes any kind of movement, from stroking the cat or playing on the Nintendo Switch to planned exercise. A moderately-active person taking daily exercise will expend up to 20% of energy use. High-intensity interval training (HIIT) and resistance training can increase weight loss and calorie burn and, according to the National Library of Medicine, may speed up your metabolic rate in the hours following a workout. 

So, does metabolism affect our weight?

Can we boost our metabolic rate to burn more calories? We are all born with a different metabolism. Genetic predisposition influences whether your metabolic rate is fast, slow or average. As does your gender. Age plays a role too, with metabolism becoming more sluggish with age. 

The impact of dietary changes and physical exercise on metabolism and calorie burning will differ from person to person depending on genetics and individual body composition. So while we can certainly make some dietary and workout adjustments to charge our metabolism, our weight is ultimately determined not by our metabolic rate, but by the amount we consume and how much physical exercise we do.
Metabolism tests look at the levels of key hormones that may affect your metabolic rate. Nabta Health offers convenient at-home testing and tailored advice.


The truth about metabolism, Harvard Health Publishing, March 2021 https://www.health.harvard.edu/staying-healthy/the-truth-about-metabolism

The acute effect of exercise modality and nutrition manipulations on post-exercise resting energy expenditure and respiratory exchange ratio in women: a randomized trial, National Library of Medicine, December 2015 https://pubmed.ncbi.nlm.nih.gov/27747847/

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