Is Metabolic Adaptation Real?

Metabolic adaptation is a hot topic in the fitness industry right now, largely driven by fitness influencers suggesting it's the primary reason people struggle to lose weight and keep it off.

But what is it, and is it something you really need to worry about?

What is Metabolic Adaptation?

To understand metabolic adaptation, you first need to know how you burn energy on a daily basis.

Your "Total Daily Energy Expenditure" (or TDEE for short) is the term used to describe the total amount of energy you burn each day. This is broken down further into four categories, being:

• Exercise activity thermogenesis (EAT), which is the energy you burn through formal exercise (i.e., weight training and cardio)
• Non-exercise activity thermogenesis (NEAT), which is the energy you burn moving about throughout the day.
• Thermic effect of food (TEF), which is the energy you burn breaking down and digesting the food you eat, and:
• Resting metabolic rate (RMR), which describes the energy you burn performing the cellular functions your body needs to stay alive.

Now of these factors, the largest determinant of your TDEE is your RMR, which accounts for around 70% of your total energy expenditure.

With this in mind, metabolic adaptation describes a process whereby your energy expenditure decreases, meaning the amount of energy you need to consume to stay the same weight (or lose weight) decreases [1].

Why Does Metabolic Adaptation Occur?

Metabolic adaptation is thought to occur when you are exposed to a prolonged period of low energy availability (i.e., during a diet).

Historically speaking, this process makes sense. 

Back when humans were hunter-gatherers, food was scarce. And during times when food was hard to come by, metabolic adaptation would be desirable because it would help you sustain essential body fat levels and survive without food.

However, in modern day, we don't have a food scarcity problem. Instead, the most likely instance of metabolic adaptation is when someone tries to lose weight. 

The Drivers of Metabolic Adaptation

When it comes to metabolic adatpation, there are two main drivers: a physical loss of weight and a change in hormone secretion.

The first one is simple to understand.

The heavier you are, the more energy you burn moving around on a daily basis. You also spend more energy on the physiological processes that keep your body running because there is simply more of you to run.

But, when you lose weight and get lighter, the amount of energy you burn in this manner decreases.

This is one of the key factors that contribute to lasting (but expected) changes in energy expenditure (and, by extension, metabolism) after you finish dieting and lose weight.

The second is a little more complex and related to the hormone leptin [2].

Leptin is a hormone produced by fat cells, but its production is only high when those fat cells are full. When you lose weight, your fat cells store less energy and literally shrink in size. This causes a reduction in leptin production and secretion.

Now, leptin plays a number of key roles in the human body, some of which include the regulation of hunger and energy levels.

With this in mind, when you enter an energy deficit and start losing weight, your low leptin levels are likely to cause an increase in hunger, a reduction in energy levels, and, therefore a reduction in NEAT -- all of which further reduces your daily energy expenditure.

So, considering this, it should be apparent that metabolic adaptation is a very real phenomenon -- but is it something that has a large impact?

The Impact of Metabolic Adaptation

Given the level of interest in metabolic adaptation, it should come as no surprise that it has been researched quite extensively -- and the results have indicated that it can indeed have a measurable impact on energy expenditure.

A well-regarded review by Rosenbaum and Leibel explored the topic in detail and found that if someone loses ~10% or more of their body weight, their TDEE will drop by somewhere between 20 and 25% [3].

But where exactly does this come from?

As I have already outlined, some of this reduction is explained by simply being lighter, but this cannot explain all of it. 

In fact, the change in TDEE tends to be slightly larger than what you would expect based on changes in body weight alone -- which means there must be an additional adaptive component.

And this can almost entirely be explained by reductions in NEAT.

Research has shown that if someone loses ~25% of their body weight, they will see a reduction in TDEE that is ~25% greater than what could be caused by just a loss of physical mass [4]. 

However, their resting metabolic rate changes will only account for about ~2% of this. This means that reductions in NEAT explain the other ~23% of metabolic adaptation.

NEAT is Important

Most people balk when they hear this because they perceive NEAT to be somewhat unimportant -- but I want to reiterate that reductions in NEAT go beyond just doing less incidental activity.

It implies that you are subconsciously becoming more efficient.

This might mean making more efficient movement strategies to get around the house. It might mean unknowingly fidgeting less to preserve energy. It might even mean taking the elevator instead of the stairs because you feel too fatigued to take another step.

Changes in NEAT are very real, and they are often outside our control.

How Long Does Metabolic Adaptation Last?

So we know that Metabolic Adaptation does happen, but the good news is that it doesn't always happen and doesn't last forever.

Firstly, metabolic adaptation is not going to happen to a notable degree unless someone is spending a very long time in an energy deficit and looking to lose a large amount of weight, or if someone is looking to get down to extremely low levels of body fat (i.e., less than 8-10%).

In both of these instances, we would expect to see a larger degree of metabolic adaptation due to the more extreme nature of the energy deficit. But if you are looking to lose a little bit of weight, it will not be a huge concern.

As you move through a weight loss phase, you will be forced to reduce calories to continue losing weight. Although you will not be able to reverse the adaptation coming from being a lighter body weight (unless you regain that weight, which probably ruins the point), the reduction in NEAT tends to return to baseline soon after returning to maintenance calories.

The reason is that losing weight is not the primary cause of metabolic adaptation, whereas being in a constant state of energy restriction is.

To minimize the already small amount of metabolic adaptation, the goal should be to increase back to maintenance calories relatively quickly after reaching your goal body weight [5]

Final Thoughts

Metabolic adaptation is indeed a very real phenomenon.

But it is unlikely that you need to worry about it unless you are looking to lose a considerable amount of weight or get as lean as a bodybuilder on stage.

If you are someone who is simply looking to lose a bit of weight so you can feel more comfortable at the beach, it is good to know that it exists, but know that it is not going to impact you in a particularly negative manner.

References:

1. Trexler, Eric T., Abbie E. Smith-Ryan, and Layne E. Norton. "Metabolic adaptation to weight loss: implications for the athlete." Journal of the International Society of Sports Nutrition 11.1 (2014): 7.
2. Kelesidis, Theodore, et al. "Narrative review: the role of leptin in human physiology: emerging clinical applications." Annals of internal medicine 152.2 (2010): 93-100.
3. Rosenbaum, Michael, and Rudolph L. Leibel. "Adaptive thermogenesis in humans." International journal of obesity 34.1 (2010): S47-S55.
4. Weigle, David S., et al. "Weight loss leads to a marked decrease in nonresting energy expenditure in ambulatory human subjects." Metabolism 37.10 (1988): 930-936.
5. Hall, Kevin D. "Metabolic adaptations to weight loss." Obesity 26.5 (2018): 790-791.

Thanks for the feedback on my fat burning zone article.

It’s true if you are carbohydrate deficient that you will begin to metabolise muscle tissue. If you are depleted in carbs and are performing a high intensity cardio session working aerobically, fat is not able to supply a sustainable energy source, simply because fat is metabolised quite slowly. Muscle tissue on the other hand is utilised far more effectively than adipose (or fat) tissue.

The key with high intensity cardio is to ensure that you do obtain adequate carbohydrates prior to your training session. A big mistake is to perform this cardio on an empty stomach first thing in the morning for this very reason – you will be carbohydrate deficient. It is also unwise to perform high intensity training when you are following a particularly low carbohydrate diet – you will most likely lose significant amounts of muscle tissue.

Hope this helps mate. Carbs are so very important when losing weight. They have received a very negative “stigma” in the past decade, but this is really due to fad dieting myths rather than sound scientific research.

Personally, I have never investigated the Lite n Easy diet program in too much detail, but I do believe that there can be many benefits by combining a healthy approach to nutrition with an appropriate exercise regime.

I have actually had one personal training client in the past that hasn't had the time to cook her dinners after a full day at work and then her workout at the gym. What we found was an effective solution in her circumstances was to order a Lite n Easy dinner every day, which worked out quite nutritionally sound. This fit in effectively with the remainder of her exercise and dietary intake. While she was losing weight, I was able to educate her as to the benefits of correct nutrition, while she was being supplied with healthy meals.

A couple of things that you need to look out for with Lite n Easy. It's a great convenience model approach to weight loss. However, you do need to ensure that you implement an appropriate exercise regime into your lifestyle in conjunction with the changed eating habits. In my example above, my client found that the integration of just one meal a day and our online personal training worked exceptionally well for her.

You also need to approach such a program as the Lite n Easy diet as a lifestyle approach. Do not expect to subscribe for a finite amount of time, lose weight and then expect to be able to revert back to old lifestyle habits. If you plan on changing your eating habits, you must implement them into the long term so you achieve sustainable results. If you plan on learning how to eat in a healthy fashion by subscribing to such a programme, you must be able to continue these healthy eating habits if you plan to eventually quit and cook for yourself.

Having said this, Liz, who wrote an article "Getting Started - A Guide for the Obese Individual" raises a very important downside to the Lite n Easy diet. She has been obese and lost a phenomenal amount of weight - yet the Lite n Easy diet failed her, but rather by hiring a personal trainer. She believes, and I agree with this based on what I have read, that the Lite n Easy approach to nutrition does not work in the long-term because they do not educate you effectively about nutrition. According to Liz, they provide you with the food and calories required to eat to lose weight, but do not teach you how to sustain this in the long-term.

So, Lite n Easy can be advantageous if approached in the correct fashion, but only in the correct circumstances. It can be quite convenient in conjunction with a personal trainer who can be your "personal co-ordinator"  between healthy eating, exercising, education and generally following a healthy lifestyle. If you would like some specific advice, please do not hesitate to contact us regarding our online personal training services.

Great question.

Research has strongly concluded to date that the most effective form of cardiovascular exercise for weight loss is high intensity interval training (HIT). Considering that there are no medical concerns and that you have been cleared by a professional (both medical and fitness) to perform this style of cardio safely, then this is the form of cardio that you should be considering.

Cardio exercise on an empty stomach with high intensity training does have significant drawbacks as I'll explain below:

Intensity

With high intensity cardio that you will be performing, the primary energy source that you will be utilising during your workout will be carbohydrate. Carbohydrate is available both from the foods that you consume and also glycogen (carbs stored within the muscles).

If you exercise having not eaten for over eight hours, your ability to source carbohydrates will be greatly diminished. Your glycogen levels will be quickly depleted and you will have no ready access to carbs from your diet. Thus, your intensity will greatly diminish. A lower intensity means that fewer calories will be expended, potentially resulting in a decreased ability to oxidise fat AFTER your workout has completed. Also, a lower intensity means that your body's fitness response will be reduced.

This also brings us to the second point:

Muscle Catabolism (or muscle breakdown)

Since carbohydrate is not readily available, your body has two other desirable (in it's eyes) options: fat tissue and muscle tissue.

Fat tissue is slowly oxidised (or broken down) - hence why it is a primary energy source for low intensity cardio. When it comes to high intensity cardio, fat cannot provide the required energy quickly enough to sustain this level of output. Consequently, muscle tissue is utilised at a higher priority. This means that a significantly higher degree of muscle tissue is broken down to generate energy to fuel your body through the workout.

In order to reduce the degree of muscle that is lost during (and after) your workout, the optimal approach is to consume a carbohydrate rich food prior to your workout, in addition to a protein source also.

Optimal Fat Oxidation (or fat breakdown)

The majority of fat loss occurs after your workout, when you go through a period of "excess post-exercise oxygen consumption" (or EPOC). The notion that it is more effective to perform cardio on an empty stomach is based on the premise that most of the fat loss occurs during your workout and thus by exhausting other energy options, you can "target" fat oxidation more effectively. However, at a high intensity, minimal fat loss occurs "during" the workout. The vast majority of fat loss occurs after the workout, during the EPOC period.

Here are a few articles for further reading that I strongly recommend you review if you haven't already:

Myths Under the Microscope - Fat Burning Zone

Great question. Often supplements geared at raising the metabolism do so through a thermogenic effect.  Thermogensesis is the process of heat production in organisms, so a thermogenic supplement aims to dissipate more heat, thus expending more energy and creating a greater calorie deficit.

Personally, I am not familiar with this particular supplement as Australia is highly regulated in the supplement industry. Consequently, all the thermogenic supplements sold through our online supplement store adhere to strict Australian standards and are often composed of different blends than are found in other countries.

I would strongly advise against taking a supplement of this nature, unless instructed to do so by a medical professional. Thinning of the blood can result in some undesirable consequences.

You’re right on the money when you suggest that raising your metabolism naturally would be ideal through exercise and nutrition. The combination of both exercise and nutrition can have a far more profound effect upon raising your metabolism and burning fat tissue than any supplement on the Australian market can do. Supplements are only of value once you have established an exercise and nutritional regime that is conductive toward your goals. From there, a supplement can “enhance” your results. Always keep in mind that a supplement is there to “supplement” exercise and nutrition – not to replace it.

You may be interested in reading more in my blog post entitled The Best Fat Loss Supplement