Tip: Keto and Bodybuilding Don't Mix

Keto revisionists are saying you can eat plenty of protein and still stay in ketosis, but they're wrong. Again. Here's why.

I've often written about how hard it is to really be in ketosis. It's not a problem if you're an epileptic in a hospital being fed a controlled diet by a team of white-gowned specialists who weigh all your food, along with all your doodie.

But if you're a regular Joe who isn't in total command of his food chain – who doesn't live on a farm and grow all his own food and make all his high fat, unsweetened, almond flour peach cobbler with no peaches – you're liable to slip up sooner or later. All it takes is eating an apple that's too big, a spoonful of hidden sugar in a sauce, or a morsel of matzo in a meat loaf.

Beyond all that is a problem that's probably unique to lifters: They eat an f-ton of protein. Every day. People who are truly in ketosis need to get 80 to 90 percent of their calories from fat, and that doesn't leave much space for protein, which is the lifeblood of a lifter.

Hell, lifters argue all the time about whether they need to eat one entire cow or two every day to best grow muscle, and most keto people, if you threaten to force-feed them a sugary churro, will admit that eating a lot of protein – more than, say, 20 percent of total calories – will take you out of ketosis.

Twenty percent might be generous, though. Even if a generic keto-er could get away with eating a diet of 20% protein, eating such a relatively small amount of protein every day would cause the muscles of most bodybuilders and lifters to start to shrink.

If you don't give your body sugar, the body will break down protein to get it, and that protein will come mostly from muscle. Ketosis itself is your body's way of trying to preserve that protein and ipso facto, your muscles. But take in a sufficient amount of carbs or protein and the body takes a pass on all that keto silliness and goes back to using sugar as its energy source.

The trouble is, there's no one guideline that works for everyone. One person might get knocked out of ketosis for having a diet that's 20% protein, and another person might get booted out for eating a lot less.

Lately, though, people who worship at the keto altar are low-carb waffling on this protein speed limit. They're saying that worries about gluconeogenesis – the process by which amino acids are converted to sugar – are overblown and that it doesn't really happen when keto dieters eat high-ish amounts of protein, at least not to the point where it knocks you out of keto.

Others argue about the actual biochemistry of the phenomenon, saying that gluconeogenesis is a non-factor, and if protein does take you out of ketosis, it's because the excess protein is donating oxaloacetate to acetyl-CoA in the Krebs cycle... but that's getting pretty deep in the biochemical weeds.

What matters is whether the amount of protein a bodybuilder or lifter needs to grow muscle – or even maintain it – is enough to take you out of ketosis, and I think it is, as do a lot of other biohackers, nutritionists, and keto autodidacts. But those who have financial interests in promoting a ketogenic diet disagree.


Some of the keto revisionists point to studies (mostly published in diabetes journals) that showed gluconeogenesis does occur after a high protein meal, but under very unusual circumstances. Even so, they maintain the amount of sugar produced amounted to just a duck snort; not enough to knock a flour beetle out of ketosis.

Granted, those studies do show that dietary proteins contribute very little to glucose production, but the test subjects weren't in ketosis in the first place. Generally, the subjects were run-of-the-mill diabetics, or healthy people who'd just fasted overnight and were then given a high protein, zero-carb meal. Sure, gluconeogenesis occurred, but as keto apologizers claim, only to a minor degree.

Fasting overnight, though, is hardly enough to deplete anyone of their glycogen reserves, so it's not surprising that a significant amount of gluconeogenesis didn't occur in these test subjects.

Keto protein-deniers need to look at studies like the one performed by Veldhorst, et al where subjects were truly depleted of carbs – fed a low-carb diet (0% carbs, 30% protein, and 70% fat) and depleted of glycogen reserves through exercise. They found that the low-carb, high-protein diet led to an increase in energy expenditure, 42% of which was explained by an increase in gluconeogenesis.

That's significant, and enough to knock anyone out of ketosis easily.

If lifters or bodybuilders want to lose fat, they'd best do it the old-fashioned way: reduce caloric intake while eating modest amounts of functional carbs and fat and striving for protein intake of between 30 and 40% of total calories.

  1. Veldhorst MAB et al. Gluconeogenesis and energy expenditure after a high-protein, carbohydrate-free diet. Am J Clin Nutr. 2009 Sep;90(3):519-26. PubMed.