How Keto Prevents Muscle Loss On A Diet

11 min read

The pendulum may be swinging in the diet world, but there’s ground to make up. People still view keto as a diet that gets the job done, but makes you feel like hell while doing it. A weapon for weight loss, but not so effective at keeping muscle. 

As a result, it tends to be used by the general lifting population as a short-term diet, saved for a sharp burst over a few weeks, rather than something to fill the entire calendar. Meaning that most of the time, it functions and ends like any crash diet. 

Even in the realms of professional bodybuilding, better seen as competitive dieting, low carb diets are rarely actually ketogenic and often get balanced out with carb refeeds to alleviate the suppressive effects of restricting carbs. 

So why is keto apparently so dangerous for muscle? The thought process follows logical lines, but then misses out on the general principle of metabolic flexibility.

The Argument : Keto’s Muscle Problem

1. You Can’t Lift Heavy On Keto

Muscle is built by lifting heavier weights, and going for the higher intensities means using glucose as the primary fuel source. With keto, that fuel source is steadily depleted as sugar intake is restricted altogether and liver and muscle glycogen lose their supply.

So without carbs in the tank, your squat sessions will be using triglyceride and ketone bodies to do the majority of the work. This energy system is slower, less explosive, so you’ll experience a drop-off in performance. 

2. The Lack Of Insulin : The Master Anabolic Hormone

To add an extra dose of whammy, muscle protein synthesis (MPS) is initiated by insulin. Which happens to be the hormone that experiences the biggest drop over the course of a ketogenic diet. While this shift is great for fat loss, as insulin usually blocks lipid mobilisation, it’s not so great for the mechanism of muscle building. 

Since a decent fat loss programme means carrying a sizable caloric deficit across a span of months, with diminished MPS, it’s hard to see how the diet won’t consistently tap away at your muscle stores.

3. The Fall In Leptin

Leptin is another master hormone, heavily influencing the levels of ghrelin, thyroid (t3), and others that modulate the energy expenditure and appetite signalling during dieting. Leptin correlates to glycogen levels, and going keto will naturally cause it to fall. 

While this is great for obese individuals with leptin resistance, low leptin in lean individuals doesn’t work so well. The resulting cascade of hormonal shifts can result in an excessive energy drain that puts the dampener on training intensity.

This is a big part of the reasoning for the popular carb cycling I mentioned before, as a large 24-36 hour spike in carbs usually gets leptin to jump up and alleviate some of the suppression.

4. Not Getting Enough Protein

Protein shows its best performance during a diet, being the most satiating macronutrient, and playing a crucial role in holding on to muscle mass during increased protein turnover. Bodybuilders naturally make the most of that, and push their intake up to insane levels. The general recommendation for lifters is pitched at 1.8 – 2.7 g/kg, but it’s not unheard of to take it above 3g/kg and give it the biggest slice of the calorie pie. 

At this point, even if you’re no longer tossing away the egg yolks, that keto diet isn’t actually ketogenic. It’s just low carb. Protein spikes insulin and can potentially be converted to glucose through gluconeogenesis, which in turn suppresses the effects of ketones. With ketones functioning optimally, you’re missing out on the main feature of the diet, and the chief source of fuel goes missing. So the recommendation for protein during a well-crafted keto programme is going to be a tad lower. 

The traditional version is as low as 10% of total calories, and although modified keto is at 25-30%, it can still seem dangerously low for someone who tends to fret about losing muscle during a three day vacation. Compared to the recommendation of 1.8 – 2.7g/kg, modified keto will work out at 1.5 – 1.8g/kg. Keeping in mind this is the flexible version, and most keto dieters don’t even go that high.

The Counterargument – How Keto Prevents Muscle Loss

To give the criticisms their due, I’ve laid out the main worries of keto. And on the face of it, it makes sense. If keto involves depleted glycogen, low insulin, low lepin, and insufficient protein, then surely the muscle is compromised? 

Except ketones are more than just a means of providing fuel, they form the frontline of the body’s fight against starvation, where losing muscle would be a last resort. It creates a state of metabolic flexibility, a shift from sugar fuelled to fat fuelled. And you don’t have sacrifice precious lean mass to get there.

1. Ketones Are Great For Strength – If You’re Keto Adapted

Now there is a good chance that you’re not keto adapted, meaning you haven’t spent a considerable window of time in ketosis. Just reaching ketosis isn’t enough to get ketones performing at the best as a fuel source. But once the body has been given a chance to settle into the new state of affairs, it can become remarkably adept at intensive exercise. Glycogen loss that typically comes with carb restriction is alleviated by a couple of factors. 

For one, ketones are perfectly serviceable as a direct replacement for most intensities, meaning glycogen isn’t needed. Ketones are fuel sparing and increase use of muscle fat during exercise. As a second point, glycogen can be synthesised with sugar, just by recycling lactate and other substrates.  

With the caveat of being keto adapted, which can take a matter of months, even lifting weights of greater that 85% 1RM, doesn’t show any decrements. Ketones are perfectly fine for strength training

If you’re still worrying, you can quell the fears by supplementing 20-40g of simple carbohydrates around training. Some straight sugar will be directly put to use by the muscles, generating extra intensity for when you’re starting to flag. This is known as a Targeted Ketogenic Diet (TKD). The spike in blood sugar gets erased as the invaders get swallowed up by the muscle, placing you straight back in ketosis.

Takeaway – There isn’t any sizable performance decrease on keto, in fact it’s likely going to swing the other way due to the energy sparing effects.

2. A New Source For Muscle Protein Synthesis

While there’s no longer enough insulin to spark MPS through the MTOR pathway, ketosis allows a key amino acid to fulfill the same role. 

Because BHB (the main keto body) now provides the majority of the body’s fuel needs, there’s less of a need to burn up amino acids directly for energy. Which results in increased levels of those proteins in the blood. Leucine specifically can now play a signalling role instead, and slots in at the top of the MTOR pathway, initiating MPS. There’s no need for the body to ramp down on creating new muscle tissues during keto.

Takeaway – BHB decreases Leucine oxidation, allowing it to increase MPS.

3. Leptin Does Fall, But Sensitivity Increases

The general consensus is that leptin levels modulate the body’s response to starvation (diet, if we’re being less dramatic), but you have to also account for the way the body regards leptin. If the brain is resistant to leptin, then the appetite suppressing and thyroid boosting effects might not be processed. Leptin resistance is far more of a problem in the general population than a lack of it. Simply put, it’s a significant risk factor in obesity.

But say we put that aside, because you’re generally quite lean, and probably don’t have any big issues with leptin resistance. Will falling leptin levels be a cause for concern? Potentially, but the level of sensitivity to the master hormone can still improve far across to the other end, and BHB specifically enhances the leptin receptors in the brain.

To put it simply, the drop in leptin is going to be alleviated in the vast majority of cases by better signalling. Less leptin, but with the same cascading effect across the body. This might not be enough for excessively lean lifters, we’re looking at sub 10% here, and that could be where a keto variation like TKD or Carb Backloading can come into play. For most people, it’s not worth dwelling on this issue.

Takeaway – Leptin drops, but leptin sensitivity increases, generating the same effect.

4. The Protein Requirement Is Lower On Keto

Remember how I’ve constantly labelled ketones as fuel sparing. This is going to play a huge role in deciding how much protein you really need. If the hypothetical bodybuilder runs the numbers and finds out that he needs 250g of protein to prevent going catabolic, he’s arrived at a sum that includes much more than protein turnover in the muscle. 

Protein forms building blocks all across the body, and muscle protein accounts for a fraction of that. Delving further, much of the ingested amino acids get burnt off as energy, rather than ending up in storage. This is partly why BCAA supplements are severely overhyped. You’re just paying extra for a sugar replacement.

Rolling back to the ketones, they diminish the use of amino acids as energy, because that’s now their job. When you go keto, you’re tapping into almost unlimited stores of energy. Therefore the proteins that do get consumed, now have better odds of making their way to the muscle pool.

Ketones themselves should be regarded as their own macronutrient. They have their own properties independent to fat cells, and BHB has been shown to have muscle protective effects. Which makes perfect sense, because keto itself is a metabolism that’s adapted to fight off starvation. That won’t go so well if the body just drops muscle at every turn, severely reducing your chances of chasing down your next meal.

The Takeaway – Ketones provide the majority of energy needs, sparing protein that can now be used for MPS.

Wrapping Up The Case For Keto

Assuming you started on the fence, or sat behind it, reading through this will hopefully have helped you realise that ketosis creates a series of complex changes that’s adapted to help you survive during times of starvation. Which any decent diet should be invoking at some point. You’re looking to disturb homeostasis enough to see real changes in shape, it’s not meant to be a cakewalk.

Since muscle is considered by the body to be essential, keto wouldn’t be doing much of a job if it just sat back and let you waste away. So there’s no real reason to worry about muscle loss while going into a diet. 

As far as bulking goes, keto may not be as optimal due to the appetite suppression working directly against your ability to overeat. And while it’s still certainly possible to add weight on keto, it’s in the realms of fat loss where keto really shines.

Find More Keto Guides And Tips On My Blog

Why I Chose To Combine Fasting With Keto

11 Ways Keto Boosts Your Brain

Hey, I’m Sama, a natural bodybuilder who’s bought into the perks of keto and intermittent fasting. Why? When combined, the boosting effect on mental energy is unrivalled on any other diet. And the fat loss isn’t bad either. 

I’ve got a ton of recipes, guides and insights covering both diets, and you check them all out on my blog.

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