Is Keto Good for Athletes?

The keto health craze is here!

And if you’re wondering whether you should try it or not (especially if you’re an athlete), you need to read this!

The idea behind the diet’s popularity is that it can train your body to burn fat as fuel. This means your metabolism changes. You stop burning carbohydrates (your body’s preferred fuel) and start burning fat (and ketones) as fuel.

You become “fat adapted.”

How is this possible? What are the risks and benefits? And how does this apply to athletes?

I hash it all out in this post.

NOTE: Before we go on, know that the whole topic of ketosis is a hotbed of scientific research now. More studies are being regularly published, so keep on the lookout for new information.

Metabolism 101 – Carbohydrates vs. Fats (and Ketones)

To change your metabolism from being carbohydrate-burning to fat-burning, you need to give it a reason to change. Your body prefers burning carbohydrates as fuel. But, we evolved the ability to use a backup fuel for times of starvation (or fasting). Even when fasting you still need to fuel your brain, heart, muscles, and other critical organs to survive. So, what does your body do when there aren’t enough carbohydrates to burn?

It turns to your backup fuel: fat.

The ketogenic diet is a diet that mimics the effects of fasting, without actually fasting. This happens when you lower a number of carbohydrates (think: blood sugar and liver/muscle glycogen) available to the point where your body goes to “plan B.”

When your body starts to tap into its fat storage, it naturally produces a biochemical called “ketones” (or “ketone bodies”).  This is why it’s called “ketosis.”

Normally (when not in ketosis), ketones only account for 5% of the energy provided to muscles. After an overnight fast, the amount of energy your muscles get from ketones goes up to 10%. It can get as high as 20%-50% after 72 hours of fasting.

Another reason why ketosis has drawn such interest lately is that it requires less oxygen to produce the same amount of energy. This makes sense if the state of ketosis is specifically for survival or starvation. Our bodies need to adapt to less food and become more efficient.

Exercise requires a lot of energy. Plus, we have much more fat storage in our bodies than carbohydrate/glycogen storage.

So, these are a couple of the reasons why athletes try to tap into the state of ketosis for improved performance. First, because when in ketosis our bodies become more efficient; second, to tap into our largest reserve of energy (fat).

How to get into ketosis

There are two ways to get your body into ketosis.

The first is by eating a ketogenic diet. As you can guess, this is a very high-fat, very low-carbohydrate diet. There are a few different ways you can do this that I cover below.

The second way to get into ketosis is by using ketogenic supplements. These are new to the market, and research is limited right now. I will give you the scoop on what we do know about these.

FUN FACT: The word “ketogenic” means the ability to GENerate KETOnes.~~~

FOR HEALTH NERDS: When there is a lack of carbohydrates, the plasma glucose (blood sugar), hepatic glycogen, and insulin levels all drop. This stimulates lipolysis (breakdown of lipids) of fat stores which liberates free fatty acids (FFAs) into the blood. It’s these FFAs that are the main substrate for ketogenesis (making ketones). Your liver uses them to produce acetylacetate (AcAc), which is reduced to β-hydroxybutyrate (β-HB).


The β-HB enters the mitochondria and is oxidized to acetyl-CoA for the Citric Acid cycle (TCA cycle). This produces ATP which is the energy needed by your muscles. Because your skeletal muscles make about 40% of your weight, they account for the highest amount of ketone body metabolism at rest.


The first way to “Go Keto” – The Classic Ketogenic Diet

Some people have medical reasons why they should eat a ketogenic diet. For example, certain metabolic disorders like “glucose transporter one deficiency syndrome” or “pyruvate dehydrogenase deficiency.”

Another reason why people “go keto” is to help with drug-resistant epilepsy. Some studies show that seizures can reduce up to 50% in some children. The children on the classic ketogenic diet need to be closely monitored to minimize side effects and ensure they’re getting enough nutrition to grow properly.

For everyone else, it’s optional (and is not without risks, as we’ll talk about soon).

The ketogenic diet purposefully reduces carbohydrate intake and cranks up fat intake. To a very large extent!

How large?

The classic keto diet requires about 90% of your calorie intake to be fat. This leaves just 10% for both carbohydrates and proteins. Many very healthy and nutrient-dense foods contain more than 5 or 10% carbohydrates (think: vegetables). And if you can’t eat a lot of vegetables, you can become deficient in many nutrients. So, this diet often comes with a recommendation to take vitamin and mineral supplements.

Also, because the level of carbohydrates needs to be so low, even the tiny amount of carbohydrates in supplements and medications need to be monitored.

Ideally, to maintain muscle mass, at least 1.3 to 2.5 g/kg of protein is necessary when on low carbohydrate high-fat diets. This can be as low as 5% of daily calories, which might just meet the requirements for the classic ketogenic diet.

It can take 3-4 weeks of eating this way for your body to fully adapt to using fat for fuel.

The second way to “Go Keto” – Modified Ketogenic Diets

There are three modifications to the classic ketogenic diet that make it easier for to maintain the state of ketosis. By “easier” I mean they require less than 90% of the daily calories to be from fat.

The first is the “medium-chain triglyceride diet” (MCTD). This modification allows 73% of calories from fat. However, it is mandatory to include a specific kind of fat called medium-chain triglycerides. This is because your liver makes ketones directly from these special fats. The MCTD recommends that MCTs make up about half of the fats ingested. This means that if you don’t use pure MCT oil, coconut oil would be your main daily fat source.

The second modification to the ketogenic diet is called the “Modified Atkins diet” (MAD). This allows 65% of calories from fat if the carbohydrate intake stays below 5% of calories.

The third modification is the “Low Glycemic Index Diet” (LGID). This one targets 60% of the calories from fat. Because it allows a higher intake of carbohydrates, the carbohydrates eaten must be low glycemic (which means they have little impact on your blood sugar).

So, there are your four standard ways to “go keto” with diet. Classic; Medium-Chain Triglyceride Diet (MCTD); Modified Atkins (MAD); and Low Glycemic Index Diet (LGID).

Who should avoid ketogenic diets?

 Yes, the ketogenic diet is strict and can be difficult to maintain. And, there are many conditions that it can aggravate. Particularly metabolic conditions like carnitine deficiency;

primary carnitine deficiency;

  • carnitine palmitoyl transferase deficiencies;
  • carnitine translocase deficiency;
  • beta-oxidation defects;
  • pyruvate carboxylase deficiency;
  • acyl dehydrogenase deficiency;
  • hydroxyacyl-coenzyme A deficiency
  • If you have any of the above metabolic conditions, don’t “go keto.”

The ketogenic diet can also have side effects in people without any of those conditions. The most common one affects between 14%-46% of people, and it’s constipation.

Other side effects include:

  • Lethargy;
  • Metabolic abnormalities (e.g., dehydration, hypoglycemia, excessive ketosis, metabolic acidosis, and electrolyte imbalance);
  • Gastrointestinal side effects (e.g., nausea, vomiting, and rarely hepatitis or pancreatitis);
  • Kidney stones;
  • Growth failure, and vitamin/mineral deficiencies and their outcomes (including low bone density and increased fractures);
  • Heart and blood fat issues (e.g., cholesterol, etc.). Interestingly, these blood fat problems seem to return to normal after people stop the keto diet.

So this is why people on medically-recommended ketone diets, such as children with epilepsy, should be monitored regularly.

The third way to “Go Keto” – Keto supplementation

Forget the keto diets; Can I just take a supplement?


The ketones your body produces internally are “endogenous” ketones. As you recall, these ketones are produced by the liver from the fats in the blood.

Keto supplements are “exogenous” ketones because they’re not made by the body. These exogenous ketones help your body get into the state of metabolic ketosis, without the restrictive diet.

They are in the form of β-hydroxybutyrate salts (β-HB) or ketone esters and they produce ketosis for 0.5 up to 6 hours. The esters are often buffered with a mineral salt such as sodium, potassium or calcium.

After taking a ketone supplement (usually a powder to be mixed with water), it quickly increases your blood ketone levels. This happens despite levels of blood sugar, glycogen, or insulin.  In other words, you don’t have to restrict carbohydrates to increase your blood levels of ketones with these supplements.

These exogenous ketones are broken down and absorbed by the gut. They get into the bloodstream and go to the liver to be metabolized.
Some of the reported side effects of ketone ester supplementation are flatulence, nausea, diarrhea, and dizziness.

Ketogenic diets for athletes

Lots of athletes are now trying low carbohydrate diets and say they have improved performance.

This is great for them!

There isn’t too much clinical research available as of now, so let’s go over what we do know, shall we?

As an athlete, you use glycogen (stored carbohydrates) as your main fuel. When it runs out while exercising/competing it’s known as “hitting the wall.” Avoiding this is the reason why you use energy drinks and gels – to ensure there are enough carbohydrates to fuel your performance.

If in ketosis, you wouldn’t burn glycogen, you would burn fat and ketones. This has the benefit of using less oxygen below high-intensity rates (improved efficiency). It also produces less lactate.

Sounds good, right?

But when your muscles use the fat and ketones as fuel, you don’t go as fast as when you’re burning glucose and carbohydrates.

Ketosis literally affects your athletic performance for high-intensity exercise.

There seems to be a lack of performance benefits for most athletes who eat low carb, high-fat diets. In fact, at least one study has shown impaired performance during high-intensity workouts.

“…benefits of ketogenic dieting for performance with a high-intensity component are equivocal.” (Burke, 2015)

It’s thought that this is because of how much muscles rely on glycogen, especially during intense exercise.

As for exercise intensity increases, the muscles shift from getting energy from blood fats and glucose, and rely more on muscle fat and glycogen for fuel. In fact, at moderate to high intensities, muscle glycogen becomes the main source of energy.

Here is a quote from Chang, et al., 2017:

“There is emerging evidence that [low carbohydrate high fat] LCHF diets could be beneficial, particularly for performance in ultra-endurance sports. Their effect on field-based sports that require repeated high-intensity activities is also promising. It appears that at least several months of adaptation to an LCHF diet are required for the metabolic changes and restoration of muscle glycogen to occur.”

So, what the science says so far is that ketogenic diet may help with endurance. Especially after eating this way for several months.

When it comes to high-intensity workouts, some studies show promise, some show no effect, and some show impaired performance.

So, what about ketogenic supplements?

Ketogenic supplements for athletes

There is a small difference between ketosis from a ketogenic diet and ketosis from a supplement. The main difference is that, with the supplements, there would still be sugar and insulin in the blood, and glycogen in the muscles.

Ketosis from supplements does a few things:

  • Allows muscles to keep their glycogen stores;
  • Decreases lactate concentrations;
  • Increases fat oxidation.

And they seem to do this, even if you take them along with a carbohydrate supplement.

Ketone supplements show improved energy efficiency (more energy with less oxygen needed). Well, at least they do in rat hearts. However, the question remains whether this is the same for human skeletal muscle during exercise. And if it is, does this translate to more power for the same amount of oxygen consumed (i.e. improved muscle efficiency)?

We just don’t know for sure just yet.
One recent study looked at two groups of cyclists who supplemented with optimal levels of carbohydrates. Some of them also incorporated a ketone supplement, and others had just the carbohydrates. The group who supplemented with both showed a small improvement in performance. They could go 2% farther (400 m) on average than those who only supplemented with carbs.

 So, there may be some benefit to aerobic competitions when supplementing with both ketones and carbohydrates. Particularly in highly trained endurance athletes. But, this was just one small study, so more research is needed.

As I mentioned earlier, there is not a lot of research just yet on the effects of keto supplements on sports performance.

“Although ketone body supplementation has been proposed to be beneficial for endurance athletes and ketone esters are speculated to be routinely used by professional cyclists, to the best of our knowledge there is currently limited information on the effects of ketone body supplementation on exercise metabolism and performance in recreational and elite athletes…In conclusion, based upon the few available data and our current understanding of ketone body metabolism during exercise in a sports specific setting, we conclude there is currently no evidence to support the use of ketone bodies as an ergogenic aid under conditions where optimal evidence based nutritional strategies are applied.” (Pinckaers, 2017)

So, the bottom line with keto supplements is that they may help, but we don’t know. More research is needed.


 The keto diet craze is here, and it may (or may not) be for you.

There are several ways to get into the state of “metabolic ketosis.” One is with the classic keto diet or one of the three modifications you can try. And, of course, there are also ketone supplements that can get you in the state of ketosis for up to 6 hours.

The keto diet is not without risks, though. Because it is restrictive, it can result in metabolic symptoms, gastrointestinal issues, as well as nutritional deficiencies, to name a few.

As for athletes, if you’re an endurance athlete, a ketogenic diet may be beneficial. As for high-intensity, the study results are a mixed bag.

“Unless you’re an ultra-endurance athlete, becoming fat-adapted or adopting a ketogenic diet probably won’t improve your performance.” (Precision Nutrition)

And when it comes to keto supplementation, there is a lot of speculation and little evidence.

“Our current understanding of ketone body kinetics during exercise is insufficient to warrant their use as an ergogenic aid in any practical sports setting.” (Pinckaers, 2017)

More research is needed (and is underway).



Burke, L.M. (2015). Re-Examining High-Fat Diets for Sports Performance: Did We Call the “Nail in the Coffin” Too Soon? Sports Medicine (Auckland, N.z.), 45(Suppl 1), 33–49., C.-K., Borer, K., & Lin, P.-J. (2017). Low-Carbohydrate-High-Fat Diet: Can it Help Exercise Performance? Journal of Human Kinetics, 56, 81–92.

LINK:, P.J., Kirk, T., Ashmore, T., Willerton, K., Evans, R., Smith, A., Murray, A.J., Stubbs, B., West, J., McLure, S.W., King, M.T., Dodd, M.S., Holloway, C., Neubauer, S., Drawer, S., Veech, R.L., Griffin, J.L. & Clarke, K. (2016). Nutritional Ketosis Alters Fuel Preference and Thereby Endurance Performance in Athletes. Cell Metab. 24(2), p256–268. doi: 10.1016/j.cmet.2016.07.010.


Cox, P.J. & Clarke K. (2014). Acute nutritional ketosis: implications for exercise performance and metabolism. Extreme physiology & medicine. 3(1), 1.


Evans, M., Cogan, K.E., & Egan B. (2017). Metabolism of ketone bodies during exercise and training: physiological basis for exogenous supplementation. J Physiol. 595(9), 2857-2871. doi: 10.111

Luat, A.F., Coyle, L. & Kamat, D. (2016). The Ketogenic Diet: A Practical Guide for Pediatricians. Pediatr Ann. 45(12):e446-e450. doi: 10.3928/19382359-20161109-01.

Martin, K., Jackson, C.F., Levy, R.G. & Cooper, P.N. (2016). Ketogenic and other dietary treatments for epilepsy. Cochrane.LINK:

Pinckaers, P.J.M., Churchward-Venne, T.A., Bailey, D., & van Loon, L.J.C. (2017). Ketone Bodies and Exercise Performance: The Next Magic Bullet or Merely Hype? Sports Medicine (Auckland, N.z.), 47(3), 383–391.


Precision Nutrition, The Ketogenic Diet: Does it live up to the hype?


Schoeler, N.E. & Cross, J.H. (2016). Ketogenic dietary therapies in adults with epilepsy: a practical guide. Pract Neurol. 16(3):208-14. doi: 10.1136/practneurol-2015-001288.


Volek, J.S., Noakes, T. & Phinney, S.D. (2015). Rethinking fat as a fuel for endurance exercise. Eur J Sport Sci. 15(1), 13-20. doi: 10.1080/17461391.2014.959564.


Volek, J.S., et al. (2016). Metabolic characteristics of keto-adapted ultra-endurance runners. Metabolism. 65(3), Pages 100–110.




Subscribe to Our Newsletter and Get Your Free Food & Hormones Ebook

Social Media