Ketogenic low carbs diet concept. Healthy eating and dieting with salmon fish, avocado, eggs and nuts. Top view

Is Keto Good for Athletes? Part 1

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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 keto diet’s popularity is that it can literally train your body to burn fat as fuel. This means your metabolism actually 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 published regularly, so keep on the lookout for new information.


Metabolism 101. Carbohydrates vs. fats (and ketones)

In order 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 in order 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 the amount 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 type of 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.


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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, or keto for short. As you can guess, this is a very high-fat, very low-carbohydrate diet. It is not a high protein diet, but rather a ‘moderate’ protein 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 fairly new to the market, and research is limited right now. I will give you the scoop on what we actually 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 (carb stored in the liver), 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 beta-hydroxybutyrate (B-HB).


The beta-HB enters the mitochondria [the cell’s furnace] and is oxidized [burned] 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 have to eat a ketogenic diet. For example, certain metabolic disorders like “glucose transporter 1 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 pretty 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 75-80% of your calorie intake to be fat. This leaves just 5-10% for carbohydrates and 10-15%proteins. These ratios do vary. Some use a 4:1 ratio of fat:carb and protein combine. 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.


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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 actually 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 as long as 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:

  • primary carnitine deficiency
  • carnitine palmitoyl transferase deficiencies
  • carnitine translocase deficiency
  • beta-oxidation defects
  • pyruvate carboxylase deficiency
  • acyl dehydrogenase deficiency
  • hydroxyacyl-coenzyme A deficiency
  • porphyria


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:


  • 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 issues 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 beta-hydroxybutyrate salts (B-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.


NERD ALERT:  For more about why ketogenic diets aren’t all about carbs and insulin, check out Chris Masterjohn’s video reviewing this is DETAIL !



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, diarrhoea, and dizziness.


In Part 2, I’ll cover some of the evidence about whether or not keto diets are good for athletes


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, and mental health.  Follow me on Facebook, Instagram and Twitter.



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