Diet Principles #2: Metabolic Adaptation

Welcome to the second article in the Diet Principles series. If you have missed the first post – Calories In VS Calories Out – Please give it a quick read as it is an essential predecessor to this article.

With that said lets get stuck into Diet Principles #2: Metabolic Adaptation.


First of all, what is the metabolism?

On a very basic level, metabolism is the process in which your body converts food and water that you have consumed throughout your day into energy. This energy then fuels everything you do, from obvious physical activity to the very basic human functions such as breathing. Your metabolism nevers sleeps or ‘breaks’, it is constantly operating from the minute you are conceived until the second you die. How efficient and well optimised your metabolism is however can vary, and this is partly due to metabolic adaptation.

You often hear people talking about their metabolism in terms of speed. For example, people may say they have a slow metabolism who struggle to lose weight. What people are talking about when they say things like this is their metabolic rate. This is how many calories their metabolism requires each day to maintain basic bodily functions. Someone with a ‘fast metabolism’ essentially burns more calories maintaining their basic bodily functions than someone with a ‘slow metabolism’ who burns fewer.

There are many factors that can determine your metabolic rate which include gender, body composition (muscle/fat/skinny etc), age, daily activity and genetics.

So what is metabolic adaptation?

The body is very smart. It is designed to survive. It will do what it thinks is right to keep you alive. How nice?

Well, it can be a bit annoying when you are trying to lose weight. When pursuing weight loss, two things happen. We impose a calorie deficit on our bodies (either by restricting food intake or increasing excercise – or a bit of both) and due to this we begin to lose body weight (mostly body fat mass). Now in our own conscious minds this is great, this is exactly the results we are looking for. Our bodies however see this very differently. It does not know that we are deliberately eating in a deficit and instead only notices that energy supply is low and therefore adapts accordingly.

To adapt your body decreases your energy expenditure or ‘slows down’ your metabolism as to try reserve as much calories as possible. It may also alter hormone levels to promote hunger (make you feel hungrier to make you more inclined to eat) as well as other hormone alterations. This is what is referred to as Metabolic Adaptation.

How does this affect me when dieting?

When your primary goal is to lose weight, metabolic adaptation can be a bit annoying. You may have began a diet and for a few weeks it is going very well and you are consistently losing weight on your weekly weigh in. Next thing you know, everything seems to have stopped. You have not changed anything. You have been consistent with your diet and exercise yet you have barely lost anything. This is because your body is adapting your metabolism to try and make up for the decrease in calories.

As a result of this you then have to either decrease your calories further or increase your exercise to put yourself in a deficit again. How annoying?

This unfortunately is what has to be done in order to continue losing weight. This is why we never recommend cutting your calories by a drastic amount when you begin to diet and only decreasing calories incrementally by small amounts. This is so that you don’t put yourself in a 500 calorie deficit and then when your body adapts,  you then have to cut even more calories. Instead begin dieting by going on a relatively small deficit such as 100-200 calories. Increase by small increments when you begin to notice the weight loss slowing down or halting altogether to keep it going. Remember losing weight is not a sprint. To be done healthily you need to pace yourself.

So does that mean you are stuck on these calories when you reach your goal weight? Absolutely not, metabolic adaptation works both ways.

Metabolic Adaptation Works Both Ways

Luckily the metabolic adaptation also works the other way. This means that after you have been dieting for a certain amount of time, say for example you have reached your target weight, you can begin to introduce more calories to your diet and allow your body to adjust to this. This is often referred to as ‘reverse dieting’. You cannot just go on a pizza binge and expect your metabolism to increase overnight however. Reverse dieting takes time and requires small increments to your calorie intake and enough time for your body to adjust to this slight increase.

The amounts you increment your calorie intake varies from person to person and by how resilient you are to staying at an exact weight. If you are not too worried about gaining a few extra pounds (say after a bodybuilding show) then these calorie increments may be slightly higher whereas the increments may be lower if you are really wanting to stay as close to your current weight as possible.

The best way to do this is again, by taking your time and pacing yourself. Choose a calorie increment and then weigh yourself after your first week on this increment and monitor how your weight has fluctuated. If you have stayed the same you can then increase by another increment. If you have maybe increase bodyweight you may want to either stick to this same increment for another week to allow your body to adapt or even slightly decrease the increment depending on just how much you are wanting to remain at a certain bodyweight.

Unfortunately after dieting, most people do not take the advice above and just begin to drastically increase their calorie intake again. This is a bad idea and is often why a lot of people end up regaining all the body fat that they have spent so much effort losing and in some cases actually end up gaining more fat than they initially started out with. This happens as the body is now burning a lot less calories than it did before due to the metabolic adaptation that took its course during the diet. A sharp increase in calories will then put your body at a much higher surplus than you may realise and therefore fast fat gain will occur. The same principle of weight loss should then also be taken when it comes to reverse dieting or adapting your metabolism to an increase in calories – slow and steady wins the race. It may be harder and take longer but it will provide better and lasting results that you will not be able to achieve by trying to rush things.


We have now had a look at metabolic adaptation and how this effects weight loss and also how you can speed up your metabolism efficiently after a prolonged perioud of dieting or once you have reached your weight goal. A more in depth guide will be posted in the near future which will take a closer look at reverse dieting so keep an eye out for this.

The next post in the Diet Principles series will take a look at Macronutrients. This is an important factor in maintaining/increasing muscle mass and keeping energy levels at as best a level as possible.

As always let us know what you think in the comments below, and if you have any questions or would like to discuss further don’t hesitate to ask.

Get Smart, Train Smart, Achieve Goals.

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