Tip: Muscle Growth During Keto

Is it possible? Some say yes, some say no. The real answer, as always, is more nuanced. Here it is.

Here's a question I received recently:

"I've been on a keto diet for 8 weeks and I've lost fat, but now I'd like to build muscle. Can I do that while on keto?"

It depends on how much time you have! If you eat enough protein and you're in a caloric surplus, you can gain some muscle while on a ketogenic diet.

However, several things make the keto diet inefficient at maximizing muscle growth. First let's look at the positives of a keto diet when it comes to muscle growth:

The Pros of Going Keto

Adequate Protein Intake

Many would say that a true keto diet isn't that high in protein. A lot of people are on a very low carb diet, but actually not in ketosis because they consume too much protein, which gets converted to glucose. But keto normally provides an ample amount of protein to support muscle growth and contribute to triggering protein synthesis. This is especially true if you're ingesting a caloric surplus.

Possible to Get Enough Calories In

While you don't have to be in a caloric surplus to build muscle, it makes the process easier and faster. And it's absolutely possible to eat a surplus when on a keto diet. After all, fat is energy dense (it provides a lot of calories per gram).

Good Hormonal Support

Diets too low in fat normally lead to lower testosterone (and estrogen) levels. This obviously won't be a problem with a keto diet, which will provide more than enough fats for sex hormone production. However, once your body has sufficient fatty acids to support hormone production, eating more fat won't lead to an equivalent increase in testosterone.

Elevated Dopamine and Adrenaline Levels

A keto diet tends to lead to higher dopamine and adrenaline levels than a diet higher in carbs. This is partly because of the higher protein intake, which is needed to fabricate both neurotransmitters, but also because of the high cortisol level that comes with a keto diet.

Cortisol increases the conversion of nor-adrenaline into adrenaline. The more cortisol you have, the higher your adrenaline will be. A keto diet leads to a higher cortisol level (all other things being equal) because one of the main functions of cortisol is to mobilize stored glycogen and break down muscle into amino acids (to be able to make glucose from them) when blood sugar is low.

Since blood sugar is lower on a keto diet, cortisol is higher. In fact, that's why a lot of people have more energy (initially) on a keto diet: more adrenaline. That adrenaline can help you train harder which helps stimulate more growth. But as you'll see in a second, it comes at a price.


The Cons of Going Keto

Here's what makes keto suboptimal for building muscle:

Lower IGF-1 Levels

Insulin facilitates the production of IGF-1 by the liver (for optimal IGF-1 production, you need growth hormone and insulin). IGF-1 is the most anabolic hormone in the body. When you go keto, insulin release is so low that it will automatically lead to lower IGF-1 levels, which decreases how much protein synthesis you can trigger.

Less mTOR Activation

mTOR is an enzyme involved in cellular growth, including muscle growth. The more activated it is, the more muscle protein synthesis you can get, and the more growth you'll stimulate. mTOR is mainly triggered by mechanical factors (stretching a muscle fiber while it's producing a lot of tension) but nutrition also has an impact. Specifically, insulin and certain amino acids (like leucine and glycine) can increase mTOR activation. While you can get the amino acids from a keto diet, you don't really get much insulin, so you'll also miss out on some mTOR activation.

However, lower IGF-1 and mTOR levels on a keto diet are actually a positive of that diet when it comes to potentially slowing down aging and even the growth of cancerous cells. It's just not good for muscle growth.

Less Insulin

Insulin is often seen as the big bad wolf of body composition. It's really not. In fact, if you want to maximize growth, insulin can be a solid ally by increasing nutrient uptake (including protein) by the muscles, increasing protein synthesis, and reducing protein breakdown. Again, you get less insulin production from a keto diet due to the very low carb intake.

More Cortisol

All things being equal, you get a higher cortisol production from a keto diet than from a diet containing carbs. The reason? One of the main functions of cortisol is to help the body bring blood sugar up when it's too low.

Keto advocates like to talk about glucagon as the hormone that'll bring blood sugar up when it's too low because it doesn't have the bad rap that cortisol does. But in truth, both work together. Cortisol is the main "breakdown" hormone in that it'll break down stored energy when it's needed.

You may need to mobilize energy either because you're in a deficit or if blood sugar is low (it can be even if you're in a caloric surplus, especially on a low carb diet).

Because you're not eating as many carbs on a keto diet, you need to rely on stored glycogen or on amino acids to regulate blood sugar levels. This will lead to higher cortisol levels. Obviously, if you need to break down muscle tissue into amino acids to maintain stable blood sugar levels, it's not great for muscle growth.

Peripheral Insulin Resistance

This is something I noticed with bodybuilders. If they spent a lot of their contest prep on a low carb diet, when it was time for them to carb up for the competition (to fill the muscles with more glycogen, making them look bigger) it just didn't work!

It seems liked the muscles remained flat and they just got bloated. By studying this phenomenon, I found out that a low carb or keto diet leads to peripheral insulin resistance as a way to try to protect the body against hypoglycemia (low blood sugar).

Essentially, when you don't eat many carbs, blood sugar will tend to be low. If it's too low (hypoglycemia) it's dangerous. One adaptation to a very low carb intake is to make the muscles resistant to insulin. This means that the muscles stop responding to it.

So when you do release insulin on a keto diet (there is some insulin release even when you eat protein) the glucose in your blood will tend to stay there instead of going to the muscles, reducing the risk of hypoglycemia. That peripheral insulin resistance makes it hard benefit from carbing up, and makes it harder to bring amino acids into the muscles – which makes muscle growth difficult.

Lower Lifting Performance

A pure strength workout (low reps, long rest periods) isn't affected that much by keto, at least not on the energy front. But there can be some strength loss due to lowered passive stability.

Heavy lifting doesn't rely on glucose for fuel. It uses mostly phosphagens. As we saw, a keto diet tends to be high in creatine. However, traditional hypertrophy training (higher reps, longer time under tension, shorter rest intervals, more volume) will absolutely work better when using glucose for fuel.

YES, ketones can work too, but they're less efficient than glucose for that type of work. If your training involves more volume and longer sets (anything from 20 to 120 seconds per set, or more), a keto diet will hurt your performance.

Caveat: Your lifting performance might increase at first because of the higher adrenaline level. This can somewhat compensate for less efficient fueling. But it won't last, as you'll see.

Greater Training Burnout

I explained how a keto diet leads to higher adrenaline levels. This can be cool at first because it gives you the illusion of more energy, drive, and motivation. But it comes at a risk: downregulating the beta-adrenergic receptors.

When adrenaline is elevated too much or for too long you can quickly desensitize its receptors (beta-adrenergic) which makes you respond less and less to adrenaline. And if you reach a point where downregulation is too pronounced, you'll start to suffer from the following:

  • A decrease in muscle strength and power
  • Less muscle tone
  • Loss in coordination
  • A drop in motivation, drive, and energy
  • Less mental acuity
  • A decrease in endurance due to lower heart contraction strength potential

This is what I call a "training burnout" and a keto diet is more likely to lead there because of the higher adrenaline and cortisol release.

Furthermore, it's harder to "calm the brain down" after a workout when you're on a keto diet. That's because carbs, by increasing blood glucose levels, are very effective at lowering cortisol and thus adrenaline. A post-workout drink with the right carbs can help you bring cortisol and adrenaline down after your session. You obviously don't get that on a pure keto diet.

Less Passive Stability

Some people call it "joint packing." I call it passive stability. Normally the tissues around a joint create pressure on that joint, and that pressure helps to stabilize the joint. Muscle volumization is one of the main elements in passive stability. If you fill up the muscle as much as possible, it expands and puts more pressure on the joint nearby.

Glycogen and water are the two main elements involved in muscle volumization. Both will decrease on a keto diet. In general, a keto diet can lead to strength loss, especially in pressing exercises involving the shoulder joint. Being the most unstable joint, it's the most at risk of performance decrease from less stability.

Can you prevent that from happening? Sure. If you do lots of exercises to improve your shoulder active stabilization and if you consume a boatload of electrolytes to try to minimize water loss. Consuming micronized creatine will also help, since it too can volumize muscle cells. But it's an uphill battle.

Here's a video for more on that topic:

You can build muscle on a keto diet, but it's not ideal. At the very least I'd include some carbs around your workout to get more IGF-1 and mTOR activation (and lower cortisol). One dose of Plazma™ intra-workout is not likely to kick you out of ketosis if it's already established and it can go a long way in helping you build more muscle on a keto diet.

Christian Thibaudeau specializes in building bodies that perform as well as they look. He is one of the most sought-after coaches by the world's top athletes and bodybuilders. Check out the Christian Thibaudeau Coaching Forum.