If you haven’t seen it thrown around Reddit, you might have heard it ballyhooed by a gym bro: ketosis just works, bro! You get to eat all the bacon and cream you can stomach, shred fat, maintain muscle, and still dominate your sport.
The very, very high-fat ketogenic diet is one of the hottest trends in nutrition, but while there are some success stories in endurance athletes, there’s very little evidence in strength sports. It may be delicious, but is it a smart pick for your next meet?
What Are We Talking About, Exactly?
Your body kicks into ketosis when carbohydrate intake is so low that the body doesn’t want to use it as a fuel source. Typically, that happens when fat makes up 60 to 70 percent of overall calories, protein 20 to 30 percent, and carbs are under 50 grams per day. It usually takes less than a day for your body to start producing ketones for fuel — a sure sign is when when your breath starts to smell of acetone, a ketosis by-product. (Incidentally, it kind of stinks. Like a mixture of fruit and nail polish remover, in which acetone is a key ingredient.)
“If you look at one of the main fuels the body can burn, carbohydrates and fat are the main two, and a layer down are the sort of ‘subfuels,’ lactate and ketones,” says Dr. Mike T. Nelson, CSCS, an adjunct professor at the Carrick Institute whose PhD focused on metabolic flexibility.
“Historically, ketones have not shown up in the body in enough quantities for the body to use unless you’re in starvation,” he explains. “But you can get there via what’s called a ketogenic diet. When you do that, your body will start producing ketones, which can then be used for fuel. Then you’re in a state of ketosis.”
Though first suggested as a therapeutic tool by the Mayo Clinic in the 1920s, it wasn’t until the late 20th century that ketosis gained popularity as a tool to treat epilepsy and other brain disorders. Some research has shown that more than half of children with epilepsy who go on the diet experience at least fifty percent fewer seizures.
That’s always been its main use: therapeutic. There’s also some shakier evidence that it can help the body to fight cancerous tumors and prevent diabetes.
It’s benefits like these that have spurred some corners of the health and fitness industry to try and stay in ketosis in their day-to-day lives. (Tim Ferriss has claimed it helped to cure him of Lyme disease, and he continues to cycle ketogenic phases to this day.)
It may also help folks to burn more fat while retaining muscle. Naturally, it’s this possibility that caused six pack aficionados to perk up and the diet to spread like wildfire. From there came communities like Ketogains, where some members can be found swearing up and down that all but eliminating carbs increases performance and aesthetics to unprecedented levels.
The problem is that while there’s some evidence that ketosis may not be detrimental for some endurance athletes, there’s very, very little clinical evidence as to whether or not it can benefit strength athletes.
But we know enough about how the body uses different energy systems to have a pretty good idea.
When It Might Not Be So Bad
The short answer: low reps.
“Since we don’t have a lot of direct data, you have to ask what energy source are strength athletes using?” says Nelson. “If we look at Olympic lifting and powerlifting, it’s extremely explosive power, the duration of time is very short, so it’s primarily the ATP-CP energy system. So, ketosis in those athletes may be OK because they’re typically doing brief high output with pretty long rest periods.”
He explains that if you’re keeping sets at between roughly one and three reps with long rest periods of three to five minutes, this may be long enough to regenerate the ATP levels (a method of intracellular energy transfer) even if you’re in ketosis.
“So I would say keto is OK — not great — but it’s OK during peaking phases where volume is very low and you’re having a very high intensity effort as opposed to high volume,” says Dr. Mike Israetel, an assistant professor of nutrition, exercise science, and public health at Temple University and co-founder of Renaissance Periodization. “The higher the total volume of work you perform in training, the more you’re going to rely on glycogen and carbohydrate to potentiate that performance. In strength sports, because the work is typically not as high in duration, people can get away with lower carbs in general.”
When It’s a Terrible Choice (CrossFit and the Ketogenic Diet?)
Functional fitness, strongman, and anything with high volume.
“The higher the volume of training, the worse keto starts to perform,” Israetel continues, saying that he would even caution against it for sets of more than six reps. “CrossFit is maybe the worst category of sports for which you should try to do keto. It’s an incredibly terrible mismatch.”
This is because functional fitness athletes do high volumes of training and a lot of work around the lactate threshold. When exercising at a high intensity for between one and three minutes, the body primarily uses the glycolytic energy system which — as the name suggests — runs off of glucose. If you’re in ketosis, your glycolytic system isn’t running properly and your performance suffers.
What’s interesting is that ketogenic folks don’t necessarily have low glycogen levels in their muscles. Remember that almost all the studies on ketogenic training have been performed on endurance athletes, and when they’re highly adapted, the glycogen levels in the muscles are often fine.
The issue is that if you’re in ketosis and your body thinks it needs to be running on ketones, you may not be able to use those stored carbohydrates effectively. Even if your body has all the pieces to run its glycolytic system, it won’t. (At least not well.)
“It’s an access issue, not the amount that’s being stored,” says Nelson. “It’s like a gas tanker truck being pulled over at the side of the road because it’s out of gas. It’s not like there’s no gas in the tanker truck, it’s that there’s no direct line to the engine.“
While the volume is typically a little lower, the same rules apply for strongman: it’s a sport that typically requires thirty to ninety seconds of more or less continuous output, which means it’s an energy system that runs best on carbs.
“As the events turn from the shorter events to the longer events like stone loading, log for reps, deadlift for reps, you would pay for ketosis,” says Israetel. “You’ll have a couple of reps missed on everything. It’s not recommended for performance.”
Endurance runners can sometimes manage well on ketosis because their sport is performed at a relatively low intensity, so an athlete can have some pretty decent performance using ketones as fuel. But while that may be true, there are still no world-class ultramarathoners who don’t eat carbs.
It’s also important to note that while it may facilitate fat loss, ketosis is probably lousy for muscle gain. That’s in part because insulin, despite misconceptions that it should be minimized at all costs, is actually highly anabolic.
“In bodybuilding circles where low-carb diets like keto are the most popular, you’ll see an interesting relationship where they’re very popular but only in fat loss stages,” says Israetel. “But in muscle gain phases, very few bodybuilders stay on low carbs.”
What About “Train Low, Compete High”?
In some corners of the fitness world, runners will train in ketosis to help their bodies better learn to use fat stores for energy and then, right before an race, they’ll consume a huge serving of carbohydrates. The idea is that the athlete will then be able to efficiently use both forms of fuel, and while it’s a nice theory, it doesn’t really hold up in practice.
“Research didn’t see much of a performance change, and that’s probably because they gave them a whole ton of carbohydrates while the machinery to effectively use them was impaired,” says Nelson, who notes that the right enzymes to effectively use carbohydrates were not present in high enough amounts. “It probably takes at least a couple of days and maybe a few weeks before those enzymes are back up and running at full steam.”
A Surprising Compromise
Ketosis makes an athlete more effective at using fat stores for energy while making him or her less efficient at using carbohydrates for energy. But in his clients (and yes, this is anecdotal), Nelson has found that a good way to produce an athlete who is efficient at using both forms of fuel is intermittent fasting.
“We know that ability to use fat during rest and low intensity exercise is highly variable, ranging from 23 to 93 percent ,” he says. “So some can use it much more effectively than others. If I think someone’s ability to use fat is impaired, I’ll have them do periods of fasting of up to twenty-four hours or even longer to get that acute change in fat use without messing up their ability to use carbohydrates to the highest degree,” he says.
He has his clients do long, slow, aerobic fasted training once or even twice per day in order to minimize insulin and train their bodies to use fat as much as possible without producing the kind of enzyme changes seen in ketogenic athletes that can reduce the ability to use carbohydrates. “I can give them carbs the very next day and they can still use them to a high degree,” he continues. “So I’m not screwing up their ability to do strength and power type activities.”
“People have been looking for the unique benefits of cutting carbohydrates out for a long time, and outside of some benefits in diseased populations, epileptics etc. there ‘s just no benefits, it just wont’ happen,” says Israetel. “Not surprisingly, there’s no big potentiation effect in anything when you remove something from your diet. So I think that situation with keto is, can it work in some places where it’s not terrible? Yes. Is it an enhancer? I’ve never seen anything it enhances outside of some disease conditions.”
We love bacon as much as the next person, but maybe don’t forget the home fries.
- Burke LM, Angus DJ, Cox GR, Cummings NK, Febbraio MA, Gawthorn K, Hawley JA, Minehan M, Martin DT, Hargreaves M. “Effect of fat adaptation and carbohydrate restoration on metabolism and performance during prolonged cycling.” J Appl Physiol (1985). 2000 Dec;89(6):2413-21
- Goedecke JH, A St Clair Gibson, L Grobler, M Collins, TD Noakes, EV Lambert. Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes. Am J Physiol Endocrinol Metab. 2000; 279(6):E1325-34.
- Helge, JW, Fraser, AM, Kriketos, AD, Jenkins, AB, Calvert, GD, Ayre, KJ, and Storlien, LH. Interrelationships between muscle fibre type, substrate oxidation and body fat. Int J Obes Relat Metab Disord 23: 986–991, 1999.
- Nelson, Michael T; Biltz, George R.; Dengel, Donald R. “Repeatability of Respiratory Exchange Ratio Time Series Analysis.” Journal of Strength & Conditioning Research, March 10, 2015
- Nelson MT, Kavalek M, Gannon R, Galpin AJ “A Case for and Against Ketogenic Diets in Athletes” Strength & Cond J: 2017, Feb;39(1) 27–31 doi: 10.1519/SSC.0000000000000269
- Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, Burke LM. “Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration.” Am J Physiol Endocrinol Metab. 2006 Feb;290(2):E380-8. Epub 2005 Sep 27.