Metabolic adaption (MA) is the process by which the body alters how efficient it is at turning the food you eat into energy. MA it is an evolutionarily conserved biological process in response to starvation, and this process makes a lot of sense when you look at it through the lens of our prehistoric ancestors. For example, when food was plentiful it meant starvation was not likely. There was no need for the body to store calories as fat for later use, so as many calories as possible were used to fuel regular biological functions such as organ function and maintaining body temperature. But, in times of famine, it was essential that one’s metabolism was extremely efficient, only using the minimum number of calories to maintain biological homeostasis because the rest must be stored as fat for later use to prevent starvation. 

Now that we understand MA in terms of starvation, it will be much easier to think about it in terms of dieting, which is how it is most often discussed today. How does MA translate to weight loss or weight gain? Let’s start out with the fundamentals of metabolism.

To understand metabolic adaptation, it is first important to understand Total Daily Energy Expenditure (TDEE) and all of the components that comprise it. TDEE is the total amount of calories that you burn in a day and is comprised of four different processes: Basal Metabolic Rate (BMR), Non-Exercise Adaptive Thermogenesis (NEAT), Thermic Effect of Food (TEF), and Exercise Activity (EA). BMR accounts for ~60% of the TDEE and is the number of calories it takes for your body to carry out regular biological functions such as maintaining body temperature and organ function during rest. NEAT can be defined as all the smaller movements you make throughout the day that aren’t necessarily conscious exercise, but that require energy such as fidgeting or yawning. TEF comprises ~10-15% of TDEE and is the amount of energy required to breakdown a specific macronutrient. For example, protein has a rather high TEF meaning to get your full caloric return, you have to invest a bit more energy to metabolize 1g of protein than 1g of carbs. Lastly, EA is the number of calories burned through exercise. So, how do all of these contribute to metabolic adaptation in the context of dieting?

Remember that MA is a response to starvation, and for most of us, dieting is the closest we’ll ever get to famine. Nonetheless, your body recognizes this net decrease in calories from dieting and perceives it as starvation, just like it did in prehistoric times. In response, each component of TDEE decreases. Your BMR decreases (costs less energy to keep the lights on), your NEAT decreases (you fidget less), and EA decreases, all the while becoming much more calorically efficient in the activity that you do perform. Concerning TEF, the TEF of macronutrients doesn’t change but the number of calories partitioned to breaking down these macronutrients decreases overall mostly due to a net decrease in calories. Changes in TEF probably contribute least to metabolic adaptation.

This process can explain two phenomena that we see quite often in fitness. First, it explains how someone can maintain a caloric deficit for a few weeks, lose weight, then suddenly stop losing weight while eating the same number of calories. After a few weeks at a specific caloric intake, one’s maintenance calories tend to shift. For example, let’s say John wanted to cut. He established his maintenance calories (the number of calories he eats per day without gaining or losing weight) at 2700 calories. To cut, John decides to decrease his calorie consumption to 2200 calories while still maintaining his current activity levels. For several weeks, John is at a caloric deficient, and thus, is losing weight. But the body recognizes this and is working to decrease John’s TDEE to balance the calories he’s taking in to the calories he’s burning. In this case John’s metabolism is adjusting so he WON’T LOSE WEIGHT. Low and behold, a few weeks later John stops realizing weight loss because his new maintenance calorie set point is now 2200, equivalent to the number of calories he’s eating per day.

There is also another phenomenon that’s been integral to fitness for years, mostly prominently observed in bodybuilding, that has metabolic adaptation written all over it. The detrimental cycle of bulk, cut, compete, OVERFEED. Let’s go back to our guy John as an example. John is a bodybuilder and he’s been dieting. Now remember, we discussed how the body perceives dieting as starvation and thus is decreasing all facets of TDEE i.e. its preparing for famine! John’s body thinks it is starving, so he is really efficient with calories, let’s say his maintenance calories are 2200, and any calories that are not used for TDEE will be stored as fat to prevent starvation. John competes in his show, wins first place, then rewards himself with a huge cheat meal from McDonald’s totaling up around 5,000 calories. John’s metabolism is primed for famine, I mean he’s been in starvation mode for the last 6 weeks, so anything above John’s 2200 maintenance calories is being stored as fat. There is new data that suggest that overfeeding like this can actually INCREASE the number of adipose cells (cells that store fat), and this gives scientific validation to the claims from bodybuilders that they gain more weight during each bulk and cutting is increasingly difficult each cycle.

Now that we understand what metabolic adaptation is and why it exists, how can we leverage this knowledge to achieve our fitness goals and avoid excess weight gain post-diet? 

To prevent the differentiation of new adipose cells and excess fat gain post-diet, it is important to perform a control refeed, or reverse diet. This is where you gradually reintroduce calories, and therefore gradually raising your maintenance calories to a comfortable amount rather than reintroducing them all at once. Ideologically, this is a simple process, but often much harder to apply. It requires keeping somewhat of a “diet mindset” after your diet is over, only introducing 20-50 calories more per week. But, long-term can allow you to increase your caloric intake while limiting weight gain.

Is my metabolism broken? How to identify detrimental metabolic adaptation.

Something that is thrown around in the health and fitness sphere is the idea of a broken metabolism. When used correctly, the term “broken metabolism” is really just referring to extreme metabolic adaptation that is detrimental to one’s overall body composition goals. Extreme metabolic adaptation usually manifests after an extended period of improper dieting, overeating, or a combination of the two. Specifically, detrimental metabolic adaptation could be an obese person whose maintenance calories are relatively low for their BMI, making it difficult not to overeat. Also, detrimental metabolic adaption could look like a former cross-country runner who has relatively high maintenance calories for their BMI, making it difficult to gain weight. Obviously, these are two extreme cases, but that’s what detrimental metabolic adaption is…extreme. For most people, this is not the reason they have trouble changing their body composition. More commonly people underestimate or overestimate their caloric intake, and this is why tracking macros, at least at the beginning, is so important. But for those who truly are experiencing detrimental metabolic adaptation, don’t worry, there’s a relatively straight forward solution.

As you might have noticed by now, a “broken metabolism” is usually a maintenance calories issue. Your maintenance calories are either too low for your BMI and lifestyle, resulting in consistent overconsumption, or too high, making it difficult to achieve a caloric surplus. To fix this problem, first identify your maintenance calories. This can be done establishing your BMR (equations such as the Katch-McArdle or Muller are good for this) then multiplying by 1.55. This will give you a rough estimate of your maintenance calories. These numbers should also be stacked up against a real-world measurement of your maintenance calories, which consists of monitoring your weight daily while also tracking calories. When your weight stays consistent for ~2 weeks, you’ve found your maintenance calorie set-point. From there, if you want to increase your maintenance calories, slowly introduce calories on a per day basis then once you reach your maintenance calorie goal, stay there for a while. A general recommendation is 50-100 calories per day until you reach your target maintenance calories, but this will be individualistic based on how much fat accumulation is tolerable. Conversely, if you wanted to go in the opposite direction and decrease your maintenance calories, slowly reduce calories until you reach your target set point, then continue to eat there for a while. 

Concluding Remarks

Ultimately, metabolic adaptation is just one part of metabolism and dieting. It factors in heavily in some cases, but realizing weight loss and weight gain starts with a collection of traits, among which the most important are adherence to a proper nutrition regimen and consistency with training. In my experience, something that aids tremendously to adhering to a “fit lifestyle” is proper training programming. This is something that all of the MAPS programs offer, evidence-based programming that help you develop consistency in your fitness practices. Starting small with a MAPS program will enable you to build a STRONG foundation so you’re ready to take on complicated biological processes such as metabolic adaption. 

Stay tuned for more evidence-based articles.