Chapter 15: Metabolic Adaptation

Chapter 15: Metabolic Adaptation

In most things health and fitness related we seek adaptation. However, from a metabolic standpoint we never want adaptation. Unfortunately, the rate of metabolic adaptation cases that exists is only increasing, largely due to the extreme nature of previous popular dietary protocols.

To start, metabolic adaptation may better be described in its plural form – metabolic adaptations. These can include changes in energy expenditure, mitochondrial efficiency, and circulating hormone levels. All of these changes will come as a result of long term caloric restriction, or any form of energy deficit, usually resulting from the pursuit of a lower bodyweight and/or leaner physique. Originally we saw this trend primarily with the physique industry (bodybuilders, etc.) and wrestlers (or other weight-class focussed sports), but most recently we have seen it crossing into nearly every population.

To better understand metabolic adaptation let’s look at each physiological component that can be affected by the dietary process.


We have discussed hormones at various points throughout this text but the hormones that will be most affected by caloric restriction or a prolonged energy deficit are leptin, ghrelin, testosterone, cortisol, and thyroid hormones (primarily T3, or active thyroid).

Recall that leptin, the satiety hormone, is also responsible for helping to regulate energy expenditure. Adequate levels of leptin are crucial for hunger regulation while in a caloric deficit.

As previously discussed, ghrelin is the hunger hormone. It will increase in fasted states and decrease after food consumption.

Testosterone is a sex hormone commonly thought to assist in decreasing fat mass while also increasing fat free mass (sometimes referred to as anabolism).

Cortisol has various roles and functions (as previously discussed), but in terms of metabolic adaptation it is essential to understand the role of cortisol in muscle protein breakdown. High levels of cortisol will yield a breakdown in muscle proteins, as well as a decrease in leptin levels which we know will decrease satiety.

Thyroid hormones, specifically active thyroid hormone T3, is largely responsible for fat loss and regulation of metabolic rate.

Clearly, every hormone listed above has an important role in maximizing lean tissue retention and body fat loss. Unfortunately each of these hormones is also greatly affected when in an energy deficit and the longer and more extreme the deficit, the more the body’s regulation of these hormones becomes affected. You are likely to see a decrease in leptin, an increase in ghrelin, a decrease in testosterone, an increase in cortisol, and a decrease in thyroid output. Based on the above information about those hormones this leaves us with more hunger, less satiety, less of an ability to burn fat while maintaining lean tissue, more muscle breakdown, and less overall metabolic function.

And the biggest problem of all is that these hormonal effects can continue even after the pursuit of weight loss has stopped!

Changes in Metabolic Rate

Recall that Total Daily Energy Expenditure (TDEE) is the sum of Exercise Activity Thermogenesis (EAT), Non Exercise Activity Thermogenesis (NEAT), and the Thermic Effect of Feeding (TEF).

In a chronic energy deficit each of these is greatly affected.

The body is amazingly smart. As body weight (and body fat) drop we usually see a drop in Total Daily Energy Expenditure. This means that the net effect of doing certain activities will yield less caloric output. Essentially the body is trying to restore homeostasis or “set point” as it is often referred to.

Naturally, as body weight and body fat decrease the number of calories burned through Exercise Activity (EA) is also decreased. Less body mass yields less energy necessary to perform an activity therefore less calories burned. What is often overlooked is that even external loads can still have a smaller effect. This is thought to be a result of skeletal muscle efficiency.

With the knowledge that most activities will yield less of a caloric burn we also see a reduction in Non Exercise Activity Thermogenesis (NEAT). Not only is this directly correlated to energy output during an activity but this is also somewhat central nervous system regulated. The brain recognizes a drop in body mass and wants to negate this. This produces fatigue and a general lack of desire to do most things previously classified as NEAT. So less activity and less of an impact from activity will absolutely yield less caloric output via NEAT.

While the Thermic Effect of Feeding (TEF) is relatively unchanged, it is still impacted in a caloric deficit. This is simple in nature, as less calories in will yield less TEF. This is not a product of reduced metabolic rate but has an impact on Total Daily Energy Expenditure.

Ultimately, the human body is always looking to navigate back to set point. Because of this it reduces the components of TDEE which results in a slowed metabolism. For the body, a slowed metabolism is great, as it will keep itself closer to a homeostatic balance, but for our clients a slowed metabolism is not great as it will only diminish the results of their efforts and can sometimes last well beyond the active diet phase.

Putting It Together

So what exactly does all of this mean for you working with your clients?

We will examine this from two perspectives:

  1. Helping your clients avoid metabolic adaptations
  2. Working with metabolically adapted clients

1. Helping Your Clients Avoid Metabolic Adaptations

It is important to understand that no matter how hard we try, we will never completely avoid the metabolic adaptations associated with weight loss and/or improved body composition endeavors. However, we can absolutely minimize them, and we can always remain aware of them. This should be the goal of any working relationship with your clients.

This is best achieved by maintaining the minimum calorie deficit needed to create change along with maintaining as much lean tissue as possible during the dietary phase.

Additionally, always having an awareness of the metabolic adaptations that will occur is necessary. By monitoring biofeedback you can ensure that the client is never too deep into any adaptation and that it won’t persist after the active diet phase. This will yield a series of caloric deficits followed by subsequent “reverse diets,” or periods of increased calorie intake, to restore hormonal and metabolic function.

2. Working with Metabolically Adapted Clients

Unfortunately, a large number of clients that you will encounter will have some degree of metabolic adaptation. This usually comes as a result of having tried several other dietary methods with no success but each effort likely yielded a larger calorie deficit than the method previously attempted. As outlined above, this is a recipe for disaster.

The current protocol to manage this, although not fully supported by science, is the reverse diet protocol. This involves decreasing the energy deficit by consuming more food, decreasing output, or a combination of both. It is important to understand that this will be fearful for a client, so the next chapter (The ART of Coaching) will be very important to this process.

It is important to understand that the goal of a reverse diet is simply to restore metabolic and hormone functions. Recall from earlier that hormones like leptin, ghrelin, testosterone, cortisol, and active thyroid hormone are negatively affected. Without proper function of these hormones, no dietary effort will be successful. Communicating this to your client is essential to their long term compliance – remember, they likely came to you wanting to lose weight, they did not come with an understanding that they have hormonal issues that need to be addressed first.

There are two reverse diet protocols commonly used:

  • A long, slow approach that consists of incremental increases
  • A quick restoration of approximate maintenance calories

The long, slow approach will be preferred by most clients as it will typically minimize any of the negative “side effects” associated with reverse dieting. And if the degree of adaptations is not severe, you will likely see progress towards the results you are trying to achieve. This occurs because you are actively restoring hormone levels at a rate that allows for bodyfat loss.

Unfortunately, the world is not full of hyper responders and the likely result with your clients will be one of maintenance and/or weight gain. The information above explains the reasons behind this but it is worth reiterating that educating your clients on this is essential to long term success.

This approach begins by a caloric increase of approximately 10-20%. The larger the initial deficit the larger the initial increase will be. From that point, assessments must be made approximately every 10-12 days. Assuming the client is still comfortable, further increases of 1-3% of total calories can be made. This process will continue until approximate maintenance calorie intake is achieved. At this point you should observe a change in the client’s biofeedback that indicates hormonal restoration. With a homeostatic balance restored you are now able to begin actively dieting the client.

The other method of reverse dieting involves simply eliminating the calorie deficit and taking your client immediately to approximate maintenance calories. This will usually come with some degree of rapid weight gain.

Choosing which method to use will come from your comfort level with your client, your ability to articulate the process, and your client’s ability to keep the big picture vision in mind. Slowly reversing can be a difficult process, especially when social media is full of “twelve week transformations.” However, seeing the scale increase rapidly can be equally if not more difficult and can lead to a client reverting back to restriction behaviors.

Ultimately both methods have anecdotal evidence to support their use so you must make the decision as to how you will move forward with your clients. It is worth noting that even the practice of reverse dieting is not yet scientifically “accepted,” so COACHING your client through this process becomes even more essential.

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