The 4 Metabolic Types - The Key To Understanding How Your Metabolism Works

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There are many genetic and environmental factors that determine an individual's metabolic type and how they respond to various dietary protocols.

At the genetic level this includes muscle insulin sensitivity, hormone levels, protein turnover ratio, cellular oxidation rate, sympathetic nervous system drive, methylation rate, mitochondrial efficiency, muscle fibre type, and brown adipose tissue.

At the environmental level metabolism is influenced by body fat, climate, gut microbes, energy intake, activity thermogenesis, and previous diet history.

Discussing each of the above in detail is beyond the scope of this guide. However, over the years in working with hundreds of people I have identified that there are generally 4 metabolic types that majority of people fall under, which takes into account all of the above.

The 4 Metabolic Types Are:

  1. Stable
  2. Inefficient
  3. Efficient
  4. Adaptable

Once you have identified which of the 4 types you fall under you will start to understand which diet strategy is most suitable for you, and why you should NOT compare yourself to other people.

Generally the stable and inefficient types are going to have the easiest time losing weight while the efficient and adaptable types are going to struggle more.

All hope is not lost though. Anyone can lose weight and keep it off if they follow the right plan for them. Each of the types has both advantages and disadvantages.

Let’s take a look at each of the types in more detail and discuss the best dietary strategies for each. Buckle up you’re in for a ride!

The Stable Metabolism

We are going to start with the stable metabolic types first because they are the easiest to address. The stable metabolism is just as it sounds. It does not fluctuate much in response to under or overfeeding. These types can gain or lose weight pretty easily simply from increasing or decreasing calories.

I am good example of a stable metabolic type. I can easily lose weight on about 3200-3300 calories but I start putting on weight if I go too much above 4000 calories. My predicted maintenance is around 3800-3900 calories, so it does not vary too much either way.

I can get all the way down to comp shape on 3200-3300 calories but to maintain a respectable body fat in the offseason I can’t go too much above 4000 calories.

I’ve even had my resting metabolic rate tested in a lab the week before stepping on stage and it was no different than in my offseason. Contrast that with some other studies where a drop of 40% in resting metabolic rate has been observed in competitive bodybuilders.

Now that may be partly genetic but it could also be that I’ve spent so many years maintaining a relatively lean condition at near maintenance calories that my metabolic set point is higher even at a relatively low body fat.

My good friend and former client Mark Carroll is another example of a stable metabolic type. When I worked with Mark to prep him for his first photoshoot we never dropped his calories below 2700 the entire 12 weeks. His predicted maintenance at that time was around 3300 calories.

Sure we implemented regular refeed days but from experience that’s generally not enough to offset metabolic adaptation unless someone has more of a stable or inefficient metabolism.

Mark is another example of stable type who can get shredded on 2700 calories but can start putting on bodyfat he goes too much above 3300 calories.

Stable types are usually meso or ecto-mesomorphs and they tend to distribute their body fat fairly evenly across the whole body. They generally respond best to a moderate protein, moderate carbohydrate, and moderate fat diet.

With these types I usually spread their macros fairly evenly across all their meals. I usually recommend a 20% deficit for fat loss and a 10% surplus for lean mass gain without too much fluctuations. I will usually incorporate refeed days with these types because they can slip into a catabolic state if left in a deficit for too long, and they can also handle them reasonably well.

The Inefficient Metabolism

Next on the list is the inefficient metabolic type. In research they are referred to as having a spendthrift metabolism. Out of all the types these guys have the easiest time getting lean and staying lean without even trying. Their challenge is actually gaining weight.

These individuals have a higher expression of genes involved in energy expenditure, and a lower expression of genes involved in energy conservation. Interestingly their resting metabolic rate doesn’t differ much from the average person. The extra energy expenditure usually comes from activity thermogenesis.

These types naturally have a higher level of spontaneous activity. They are the fidgeting type. Fidgeting alone can burn up to 1000 calories per day. On top of that they dissipate more heat during physically activity equating to greater caloric burn. In other world when an inefficient type walks from point A to point B they will burn more calories than the next person.

Studies have also shown that when you overfeed inefficient types their energy expenditure goes through the roof, making them more resistant to weight gain. On the other hand when you reduce their calories their metabolism doesn’t drop much.

Inefficient types are usually ectomorphs. They tend be naturally quite lean and are generally high strung individuals who secrete a lot of stress hormones. That’s why they are sometimes referred to as hard gainers.

In a mass gain phase they will generally need to take their calories to 20% above baseline or more. On the plus side when they do gain weight they will usually gain mostly muscle and very little body fat.

Loosing fat for them is fairly easy but they are also more prone to muscle loss when in a deficit. I usually recommend no more than a 15-20% deficit for them.

They generally do best on a higher carb diet because they have good muscle insulin sensitivity and the carbs help manage their cortisol levels throughout the day. I will generally give them carbs with every meal especially before training .

Here are two examples of inefficient metabolic types that I have worked with in the past.

The first example is Isaac. Isaac was already very lean when we started. He was sitting at around 7% body fat on the skinfold callipers. His goal was to gain mass. We ended up taking his calories to 120% of his predicted maintenance and kept him there for almost the entire 12 week block. At the end he only gained 0.5% body fat and 6-7kg of lean mass.

Isaac spend nearly 12 weeks in a caloric surplus and the whole time he only gained 0.5% body fat.

The second example is Matt. I helped Matt prepare for his first Men’s Physique contest. He was already lean when he started his prep sitting at around 10% on the skinfold callipers. We ended up dropping him to 5% in about 12 weeks without any lean mass loss. He actually gained a small amount of lean mass.

The entire time his calories never dropped below 80% of his predicted maintenance and his carbs never dropped below 50% of his total calories. Every 3rd week we actually spiked his calories to 120% of maintenance which coincided with his deload weeks. We used those deload weeks and the increase in calories to offset muscle loss.

Even to get stage ready Matt never dropped below 80% of his maintenance calories and every 3rd week we took him to 120% of maintenance.

Of all the types the inefficient types respond best to more aggressive and/or prolonged refeeds. Longer refeeds can help them prevent or reverse muscle loss and their metabolisms adapt upwards so quickly that they can get away with the extra calories without spilling over.

The Efficient Metabolism

Efficient metabolic types are the opposite of inefficient types. In research they are referred to as having a thrifty metabolism. They’ve been shown to have more efficient mitochondria which enable them to conserve energy instead of dissipating it as heat.

In these types if calories go up, energy expenditure does not increase proportionally and they are much more likely to store the excess calories as fat. On the other hand during caloric restriction their highly efficient metabolism allows them to extract more energy from fewer calories making them more resistant to weight loss.

They are also much more likely to regain weight after a diet because their metabolisms downregulate more than any other type and it takes a while for them to come back up. If they come out of their diet too quickly not only are they likely to regain all the weight they lost but potentially gain back more.

While it may sound like the efficient types are doomed when it comes to fat loss I can assure you that is not the case. Our genes are expressed in accordance with our environment. From an evolutionary standpoint thrifty genes helped ensure our survival in times when food supply was scarce and we were much more physically active.

Up until 40 years ago we did not have an obesity epidemic and our DNA has not evolved since then. Diet and lifestyle are still going to play a major role.

Efficient types are generally endo or endo-mesomorphs and they tend to distribute the majority of their fat around the trunk and upper back. Because central adiposity has been linked to inflammation and insulin resistance these types will generally do best on a lower carb, high protein diet.

In these types a lower carb, high protein diet helps manage their blood sugar levels, improves satiety, reduces cravings, and increases the thermic effect of feeding. I generally recommend starting them out on a 30-35% deficit. In some cases you may need to go even lower. Once they lean out you can start increasing calories and carbohydrates gradually.

On the plus side these guys can generally gain and/or maintain muscle mass fairly easily. Remember every negative has a positive and vice versa. In a mass gain phase I generally don’t recommend taking them too much above their maintenance calories.

Also these types generally don’t do well with aggressive refeeds because their metabolism is very slow to adapt upwards. When I use refeeds with these types I generally let them have a couple of hundred extra calories when they feel like they really need it to prevent them from crashing or binging.

Here are two examples of efficient metabolic types that I’ve worked with in the past.

The first example is Tony. Tony was very overweight when he first came to see me and he was also very inflamed from years of no exercise and very poor eating habits. But in only 5 months he dropped 30kg of body weight.

With clients like this I like to use a more aggressive approach in the beginning because loosing weight alone will improve a lot of their metabolic markers. After that we focused on reintroducing more calories and carbs into his diet so that he could maintain it.

Clients like Tony will generally need to restrict calories and carbohydrates more aggressively in the beginning then gradually add them back in as they lean out.

The second example is Navid. I am using a very different example here to illustrate a point. Metabolic efficiency exists along a continuum. No two people are exactly alike. Navid was much leaner than Tony to start off with and he was also carrying a lot more muscle mass. His goal was to get shredded for a physique competition.

His metabolism was still very efficient thought because we had to gradually reduce his calories from 3400 all the way down to 1700. That is substantially lower than I take most of my other guys even for comps.

To get comp shredded Navid had to reduce his calories all the way from 3400 down to 1700.

On the plus side, in the offseason he can grow muscle like a weed, he just has to be careful of putting on too much body fat by increasing his calories gradually.

The Adaptable Metabolism

Adaptable metabolic types have a tremendous capacity to adapt in both directions. During caloric restriction they respond more like an efficient type and conserve energy, while during overfeeding they respond more like an inefficient type and their energy expenditure increases significantly.

As a result they are able to maintain their body weight within a fairly narrow range at relatively high and low caloric intakes. This is highly beneficial for someone simply trying to maintain their weight because they can almost eat whatever they want.

On the other hand if they are trying lose weight or gain weight they are going to encounter the same problems as the efficient and inefficient types. They will generally need to drop calories quite low to lose weight, and they will need to go quite high to gain weight.

From my experience adaptable types are usually females, especially those with a gynoid body type who store the majority of their body fat around the hips, buttocks and thighs. This could at least in part be mediated by Estrogen which has a dual impact on metabolism.

Estrogen improves leptin and insulin sensitivity and helps regulate metabolism. On the other hand Estrogen upregulates alpha2A-adrenergic receptors which makes mobilizing body fat a lot more difficult. Most females have a much higher concentration of alpha2A receptors around the hips, buttocks and thighs which is why those are often referred to as the stubborn fat areas.

My wife Clair is a good example of an adaptable metabolic type. She can maintain a fairly lean physique on around 2200-2500 calories per day, but whenever she’s had to get ready for a show and lose that last bit of stubborn fat she’s had to go below 1400 calories.

My wife Clair 7-months post pregnancy on 2200-2500 calories per day.

Now when you start approaching very low body fat levels everyone’s metabolism will compensate to some degree but there is a huge variance between individuals. I’ve also worked with plenty of people at higher body fat levels with very adaptable metabolisms.

I’ve had some clients increase by more than a 1000 calories per day when reverse dieting without gaining any bodyfat, yet we still had to bring them down to almost where they started to get them losing.

An argument can be made that they didn’t stay at maintenance long enough for their metabolic setpoint to reset, and there is probably some truth to that. However, the time course needed to stay at maintenance may be a lot longer than most people are willing to commit to.

A good example of this is one of my former clients Kat. When she came to see me she had already spent 8-9 months in a mass building phase. During her mass building phase she had progressively taken her calories up to 2700 per day and had gained a fair bit of lean muscle while maintaining her body fat around 25%.

She thought she was going to cruise through her cutting phase because of how much she had increased her muscle mass and her metabolism. However, to keep her losing body fat we still had to gradually take her below 1700 calories over the course of 12 weeks.

That was even with incorporating structured 3-day refeeds every 11 days for the first 6 weeks. We eventually dropped the 3-day refeeds because they weren't doing much to preserve her metabolism and were just slowing down weight loss. From that point she just took single day refeeds as needed.

Kat had spent 8-9 months at 2700 calories with minimal fat gain but she still had to eventually drop below 1700 calories to continue losing body fat.

Adaptable types can handle longer and/or more aggressive refeeds pretty well in terms of not spilling over but then they adapt back down so quickly that the effects on metabolism are negated. I usually prefer giving them short refeeds when needed to prevent them from crashing, then every 6-12 weeks giving them a full 1-2 week diet break to reset.

So what metabolic type am I?

After all that you might be wondering where does that leave you as far as what type you are. In reality pure types are rare. I used more extreme examples here to illustrate a point but most people usually lie somewhere along a continuum.

Everyone’s metabolism is adaptable to a degree. The questions is to what degree does your metabolism adapt in either direction?

If you can gain or lose weight pretty easily chances are you have more of a stable metabolism.

If you can lose weight easily but have a hard time putting on weight chances are you have more of an inefficient metabolism.

If you can gain weight easily but have a hard time losing weight chances are you have more of an efficient metabolism.

And if you don’t gain weight easily but also find it hard to lose weight chances are you have more of an adaptable metabolism.

Use the guidelines above for yourself or your clients as a starting point then fine tune it from there in accordance with the needs of the individual. As you have seen everyone’s metabolism behaves differently and there is no one size fits all approach.