What Is Metabolic Adaptation?

Metabolic adaptation, also known as adaptive thermogenesis or metabolic damage refers to the slowing down of one’s metabolic rate (metabolism) after long-term undereating and substantial fat loss in an attempt to preserve stored energy (body fat).

There is always a lot of conversation in the fitness industry about metabolism, metabolic damage and metabolic adaptation. The latter two are in fact the same thing. Albeit adaptation is a far more accurate description of the physiological events taking place.

Understanding how your metabolism works is key to understanding the impact this can have on your goals and key to ensuring you recognise when adaptation has occurred and that you need to change your strategy. It’s not voodoo, it’s not some evil process your body initiates to some unlucky folk in order to keep them overweight, it is a natural and logical metabolic change that can be managed successfully.

What is metabolism?

Your metabolism is made up of several chemical processes that occur within the body, the sum of which equates to your ‘total daily energy expenditure’, or TDEE. Put plainly, this is the number of calories you use for energy each day. So what does TDEE consist of?

Basal Metabolic Rate (BMR)

This is the sum of all bodily functions needed to keep the body alive. Things like breathing and the processes our organs go through each day.

I’m sure you’ve heard the terms ‘fast’ and ‘slow’ metabolism and likely heard this used as a reason for weight gain or loss. A review by William T Donahoo et al, from the University of Vermont, USA shows that extremes are pretty rare, 96% of people are within 200-300 kcals of the average human metabolism and there is very little to correlate weight gain or loss with the BMR — those with higher or lower than average BMR usually eat to compensate for the difference.

Thermic Effect of Food (TEF)

Thermic effect of food or TEF refers to the number of calories needed by your body to digest, absorb and metabolise the food you eat. For an individual consuming a standard, balanced diet, around 10% of the calorie intake will be used by your body to process the food, so a relatively low level. However, different macronutrients require differing amount of calories for this process.

Fats - 9 cals per gram with a TEF of 0-3%

Carbs - 4 cals per gram with a TEF of 5-10%

Protein - 4 cals per gram with a TEF of 20-30%

You can see that protein, therefore, contains a low amount of calories and you get a much higher amount of those calories being used for digestion. It’s plain to see why high protein diets work right? You take in fewer calories compared to dietary fats and your body expends significantly more via TEF. Not to mention, it’s muscle-building properties and (as if that wasn’t enough good news), it’s also very satiating, so you feel fuller for longer.

Exercise Activity Thermogenesis (EAT)

As you would expect, this is the sum of energy utilised for exercise of the conscious kind. So running, resistance training, HIIT etc would all fall within this category. This can range from 15% up to 50% of the TDEE, depending on the activity levels of an individual and is something we have control over. We can’t make big changes to how many calories our body use to function and using protein to increase the TEF can only go so far, but we can increase our exercise levels to burn additional calories and create a calorie deficit, eliciting weight loss.

Non-Exercise Activity Thermogenesis (NEAT)

NEAT accounts for all your subconscious physical activity. Activities such as fidgeting, we all know someone who fidgets, bites their nails, or is constantly on the go with chores, cooking etc. These activities all need fueling and will all be adding to the NEAT levels. This also accounts for a good chunk of energy expenditure and is well within our control to impact in a positive way. For those with a desk job, getting up and walking every 30-60 minutes will have a positive impact on your NEAT.

Now we understand what metabolism is made up of, that it rarely differs between people to extreme levels and how it can be increased, let’s look at how metabolism can be adapted.

Decreased TDEE

It’s a logical conclusion that losing weight reduces your TDEE. You will inevitably be eating less food (albeit, lots of protein, if you are dieting smart), you will have decreased in size so there will be a nominal drop in the amount of energy needed to sustain your body (the heavier you are, the harder your body needs to work - this is not a positive thing!) and due to reduced calories, your body is more sensitive to various hormones that regulate how the energy you expend is used. In short, your body will expend fewer calories in activities to control hunger levels and conserve energy for the vital roles it is needed for.

The good news is, as a sensible dieter, you won’t be in a calorie deficit forever. A diet that reduces calories to below the TDEE should be a short term measure to reach a healthy weight, it’s not a long term approach. When you do return to normal energy balance (calories in balance with calories out) in order to sustain your fab new weight and an awesome body, your BMR will progressively return to normal. Many dieters who hit plateaus use this is a tool to kickstart weight loss again. A ‘reverse diet’, ‘diet break’ or ‘refeed’ can be used to trick your body into thinking you aren’t dieting so hard. Calories consumed is increased for a period of time, hormone sensitivity is reduced, the body realises that there are now additional calories at its disposal, and the body may be happy to start upping the calories it expends on activities, this is when you would return to a calorie deficit with the advantage of a higher TDEE.

Increased TDEE

Some sure-fire ways to increase your TDEE are by leveraging the influence you can have over NEAT and EAT. Exercise regularly, focus on anaerobic activities (high-intensity exercise, such as weightlifting, HIIT or short intense bursts of running) which will burn calories even after exercise and build muscle – muscle needs energy so you’ll burn more calories, increasing your TDEE. Move often and avoid long sedentary periods with regular breaks from your desk. You should, of course, not forget to eat a protein-rich diet, containing between 1.4 - 2 grams of protein for each kilogram of bodyweight.

What have we learned?

Does losing weight slow down your metabolism, yes, of course, you are a smaller person and your body therefore needs to work less hard to maintain its functions. But, does it slow down to such an extent that you can no longer lose weight? Absolutely not. You just need to understand what your new TDEE is and use that to fuel your nutrition and training. Changes to your body aren’t barriers, they are the catalyst for change and that change will allow you to reap rewards.