Metabolic Adaptation

Metabolic Adaptation

Previously I discussed why fad diets and restrictive eating often don’t work in the long term. This article is going to continue that conversation and look a little closer at something called metabolic adaptation. 

At the beginning of a diet, many people start out by eating less and they start losing weight right away, until eventually the weight loss stops or slows down drastically, this is what we call metabolic adaptation. Generally, when people stop losing weight they go back to their previous eating habits and the weight returns. Read on to find out why this happens, how to avoid hitting a plateau, and how you can avoid gaining the weight you lost back.


  • Basal Metabolic Rate (BMR): how much energy (calories) your body needs to function per day at rest, this does not account for your activity level. Accounts for 60% of Total Daily Energy Expenditure (TDEE).
  • Non-Exercise Adaptive Thermogenesis (NEAT): Smaller movements you make throughout the day that require energy, such as fidgeting or yawning.
  • Thermic Effect of Food (TEF): Accounts for 10-15% of TDEE and is the amount of energy required to breakdown a specific macronutrient.
  • Exercise Activity (EA): Number of calories burned through exercise.
  • Total Daily Energy Expenditure (TDEE): the amount of energy (calories) you burn per day. TDEE = BMR + NEAT + TEF + EA
  • Metabolic Adaptation (MA): the process of how efficient your body is at turning your food into energy. 


Metabolic adaptation (MA) is an evolutionary biological process that acts as a response to starvation. Think about it in the sense of our prehistoric ancestors. When there is plenty of food, starvation was not a threat to your body. When there is no need for the body to store food/calories as fat for use later (because there is plenty of food around), calories are used to fuel regular biological functions, like organ function, body temperature, hormone regulation, etc. In times of starvation, such as famines, people's metabolisms had to be extremely efficient and only use the minimum number of calories required to maintain body functioning. The rest had to be stored for use later, to prevent starvation.

To apply this concept to modern day dieting we need to look at the fundamentals of metabolism. 

Let’s start with Total Daily Energy Expenditure (TDEE) and what it's comprised of. Your TDEE is the sum of your BMR, NEAT, TEF, and EA. Your BMR is the amount of calories you need per day to maintain your body’s functions at rest (body temperature, etc…). NEAT accounts for the energy you need to perform smaller movements throughout the day such as yawning, coughing, or fidgeting. TEF is the amount of energy it takes to break down a specific macronutrient. This can differ because not all macronutrients are broken down the same. For example, it takes more energy to metabolize 1g of protein compared to 1g of carbs. Finally, EA accounts for the number of calories burned through exercise. Now let’s look at how all of this applies to dieting.

When we start a diet our body recognizes the drop in calories as starvation, comparable to when our ancestors went through a famine in prehistoric times. As a result, each of the components that contribute to the TDEE are decreased, so that your body can continue to function with a lower number of calories. 

This explains a few things. One is how someone can maintain a caloric deficit for a few weeks or months, lose weight, and then suddenly stop losing weight while eating the same number of calories as they did at the beginning of the diet. After a few weeks at a specific caloric intake, the amount of calories our body is able to process changes to match the number of calories you are eating. 

For example, let’s say Sarah wanted to lose 30 pounds. First, she determines her maintenance calories to be 2200 (the number of calories she needs per day without gaining or losing weight). Sarah decides to go on a diet that decreases the number of calories she is eating to 1500 calories per day, while keeping her exercise the same. For a while Sarah is in a caloric deficit and is losing weight. However, Sarah’s body recognizes that the number of calories she is consuming has decreased, but her energy expenditure has stayed the same. In order to balance the calories that are coming in with those that are going out, Sarah’s metabolism adjusts so that she won’t lose weight (our body does not want to lose weight, it wants to hold on to that energy so it can use it later). Now her metabolism has balanced with her caloric intake meaning her body is now accustomed to burning 1500 calories a day, the same number she is eating per day. This tells us that our metabolism is dynamic, meaning it changes. So after a few weeks or a month of being in a calorie deficit, Sarah now realizes she has stopped losing weight. 

Now let’s look at the second thing that happens with metabolic adaptation. Many people will get frustrated at this point (where they aren’t losing weight while on a diet) and decide to quit the diet and immediately go back to what they were doing before the diet. In Sarah’s case that means she starts eating 2200 calories per day. After a week of eating 2200 calories per day Sarah realizes she has gained weight back. Why is that? Well, Sarah has trained her metabolism to be able to process 1500 calories per day, 1500 is her new maintenance calorie number. Overnight, she increased her caloric consumption by 700 calories and her body doesn’t know how to process that many more calories at once anymore. Anything above her maintenance number can be stored as fat, because her body has been in starvation mode for the last 5 weeks. 

What does all of this tell us? Metabolism is not static, it doesn’t stay the same, if we lower the number of calories we are eating our metabolism does it’s best to find homeostasis and will slow down to match how many calories we are giving it. Now that we know all of this, how can we use this knowledge to benefit our overall health and sports performance and avoid excess weight gain?

If you are at the tail end of a diet and want to quit the diet but don’t want to gain the weight back, you’ll most likely have to go through a refeed or reverse dieting period. Instead of reintroducing more calories all at once, reverse dieting is when you gradually reintroduce calories to your diet; which gradually increases your maintenance calories to a comfortable amount. It can be a slow process and requires a diet mindset, because you might only introduce 20-50 more calories each week. In the long run the slow introduction of calories allows you to work back up to that maintenance level without gaining weight back.


Most people want to change their body composition in one way or another. Most commonly the goal is to lose weight (body fat %), or to gain muscle. You can now use what you know about metabolic adaptation to help you reach your goals. But where do you start?

In order to figure out what changes you need to make, you have to know what and how much you are eating right now. I recommend using an app like myfitnesspal to log all of your food. The majority of people underestimate how much they are eating so don’t be afraid to measure. Once you know how much you are eating, this tells you how many calories your metabolism is currently able to breakdown. If your calorie intake isn’t consistent than your metabolism is constantly trying to catch up with how many calories you consume each day. 

Nutrition coaches can use the process of metabolic adaptation and other components of nutrition to help you determine what you are putting in your body, what you need, and how to make changes to reach your goals! If you start working with a nutrition coach and they don’t ask what you are eating now before making recommendations, I’d encourage you to ask them how they know those changes will help if they don’t know what you’re already doing or not doing. 

If you have questions or are confused about metabolic adaptation please reach out to me via email: 

Happy Training!
Tunnel Marathons Personal Trainer