“Losing weight is a constant battle”. This is what most of my patients say.

Despite all the diets, medications and strictly following the advice by experts, weight loss is elusive. People do lose weight only to put it back on. Why is that? In this article, I will discuss metabolic adaptation.

Some people resign to the fact that “slow metabolism” runs in their family. The feel they are now condemned to live off lettuce to prevent weight regain while others can indulge in lush food and never gain a pound. I also hear people say that they destroyed their metabolism when they went on a diet. They usually blame the following diets

  • Very low calorie diet
  • Low Carb diet
  • Atkins diet
  • High protein diet

People feel they have messed up with their metabolism and metabolism is so slow that no matter how little they eat, they struggle to lose weight.

Does metabolic adaptation actually exist? we will discuss this after understanding some basic facts about our metabolism


How does metabolism work?

To explain what happens when we diet, it is worth first talking about our metabolism. There are three ways our body uses energy.

Firstly, there is the energy that we use to keep our body alive and functioning properly. This constitutes around 65-80% of all the energy we burn. Energy is used to keep all the vital organs in our body functioning.

Secondly, our bodies also use energy to digest our food and this constitutes 10% of all the energy we use.

Lastly, there is the energy that we use when we move around or exercise, accounting for 10-30% of total energy.

As you can see, exercise or any activity normally uses up to 30% of the total energy intake.

The speed of our metabolism or in other words our metabolic rate varies from person to person. Metabolic rate depends on several factors. These factors include our sex (women tend to burn fewer calories than men), age, level of fitness, amount of muscle mass, weight (heavier people generally have higher metabolic rates to meet the need of their bigger bodies) and of course the underlying genetics.


Energy balance

To maintain weight, we need to provide energy at a level our body uses it. This means that if we eat more energy than your body needs, we will gain weight and conversely if we eat less than our body’s demands, we will lose weight. This however is not a straight line. There are several factors in addition to energy in/energy out theory which accounts for weight loss.

Now, if food is abundant and easily available, we will use the energy that comes from it, to ensure our body functions properly. If, on the other hand, the food is limited and our body receives less than it needs, it will be forced to become very efficient and use up as little of the available energy as possible to support our body’s functions. Scarcity of food would lead to storing energy as fat so as to be used at later time.

This is a survival mechanism often referred to, as metabolic adaptation. Metabolic adaptation means the ability of our bodies to adjust its metabolism according to what we eat. Metabolic adaptation is, therefore, our body’s natural response to starvation, which in our society most often comes in the form of dieting. When we diet and lose weight our energy requirements go down.

The following changes can happen when we diet:

  • The energy used to digest our food goes down because we eat less
  • The energy used to maintain our bodily functions decreases because our body becomes smaller
  • We burn fewer calories during exercise because we weigh less

Eating less means we feel more hungry and are more prone to food cravings and are at bigger risk of giving up on dieting.


Metabolic adaptation and weight loss

Let us go through a scenario, which most of you are familiar with.

Sally needs 2000kcal every day to maintain her current weight. She eats that amount consistently and stay the same size. Then one day she decides to lose weight. She cuts her calorie intake down to 1600kcal. The number on the scales starts going down for a while. Then all of a sudden, she  stops losing weight and maintains her new weight, despite still eating as little as 1600kcal.

Why is that?

Her body adapted to the smaller supply of calories to prevent further weight loss and starvation. This means that 1600kcal is her new maintenance level of calories, which will keep our weight stable. That is her new Basal Metabolic Rate(BMR). In order to continue losing weight she would have to either cut more calories or increase her physical activity. At some point, this may become impossible as her calorie intake is already low and it is difficult to sustain such a low-calorie diet without feeling hungry or run-down. Metabolic adaptation ensures she gains weight so as to ensure she is able to function well, physically and mentally.


What is the standard advice for weight loss?

Please see below the standard advice provided by nutritionist for weight loss.

1. Up your protein intake. Not only will protein help you keep your muscle untouched during your weight loss and will make you feel full for longer, but it will also use up more energy to be digested than either carbohydrates or fats.

2. Eat your 5 a day. Remember to have plenty of fruits and vegetables throughout the day. These contain fibre and are low in calories but high in volume so will keep you satiated for long

3. Choose healthy carbohydrates. These will give you the energy to stay active

4. Adjust your intake if your weight plateaus. You will need to lower your calorie intake further to continue to lose weight so be prepared to adjust your portions

5. Stay consistent. It can be challenging to always watch your intake and occasional slip on the way will happen. However, as long as you get back on track straight away, it shouldn’t jeopardise your progress.

6. Stay active. A combination of resistance training and cardio would be best but any activity is better than no activity at all. You can introduce small changes at the beginning. Stand when you commute, take the stair rather than a lift, get off one stop too early and walk.

7. If you struggle to estimate the amount you eat, you can start tracking your intake to gain an idea of what you get with your food.

8. Be patient. Weight loss should be slow and steady, and calorie restriction possible to stick to. Therefore, it is best to take small steps and aim for weight loss of approximately 0.5-1% of your body weight per week.


Science behind metabolic adaptation?

Restrictive diets leads to successful short-term weight loss, however  most people regain the lost weight.

Physiological compensatory changes and adaptations results in overeating. During metabolic adaptation, there is  decrease in energy expenditure, fat oxidation and changes in anorexigenic hormones levels(Leptin).

In addition, there is increase in appetite, craving, increase in hunger hormone( ghrelin) and other complex psychological and neurological changes in the brain.


What is the solution to prevent weight regain?

We are different genetically, physiologically and we all I’ve in a different environment. Solution should be individualised. this is why, no diet works for every one. In the last 40 years no country in the wold has shown that their obesity prevalence has come down.

Individual assessment by a specialist and treating the underlying problem is the key to long term solution.


Simplyweight’s Specialist Online Weight Loss Plan has been designed to bring decades of clinical experience to people at an affordable price. To learn more, start your 7-day free trial today: https://app.simplyweight.co.uk/subscribe/free-trial



Dr C. Rajeswaran FRCP(UK);MSc
Consultant Physician
Obesity, Diabetes & Endocrinology