Nutritional ketosis and exogenous ketones for performance

Before we begin on ketosis, please note this is not intended to discuss all of the research around ketosis, as science has proven its therapeutic benefit for the treatment of chronic conditions including epilepsy, cancer and type 2 diabetes. Rather, this article serves as a summary of the key points, benefits and areas of considerations for those with metabolic and/or performance goals.

 What is ketosis?

Ketosis (noun): a metabolic state in which some of the body’s energy supply comes from ketone bodies in the blood, in contrast to a state of glycolysis in which blood glucose provides most of the energy.

Essentially, ketosis is a metabolic state in which you’re predominantly burning stored fat for fuel and converting fat into ketones to be used by the cells. The ketone bodies, acetone, acetoacetic acid, and beta-hydroxybutyric acid (BHB), are usually formed either when liver glycogen is low, or via metabolism of medium chain trigylcerides (MCTs). Ketone levels are regulated largely by the hormones insulin and glucagon.

The exact definition of ketosis refers to blood concentrations of ketone bodies over 0.5 mmol/L, however 1.5-3.0 mmol/L is considered optimal nutritional ketosis and is recommended for maximum metabolic benefits. Please note: these levels do not apply if you are using ketosis for the therapeutic benefits mentioned above.

How to get into nutritional ketosis

  • Low carbohydrate, higher fat (LCHF) nutrition. Find out more and learn what you can eat in our LCHF 7-Day Meal Plan here. For most people, carbohydrate intake will need be <50 grams per day.
  • Smart training, utilizing fasted aerobic training, lowering the volume of intensity, and lifting heavy weights.
  • Lifestyle strategies including stress management, adequate recovery, good sleep and moderating your caffeine intake (a Bulletproof Coffee pre-training is an excellent strategy, but excess caffeine can disrupt your blood sugar control).

 A quick note on measuring ketones

Ketones can be measured by breath, urine or blood. There are two inherent problems here in regards to athletes:

  • The available devices are often based on the metabolically unhealthy, so reference ranges may not apply to healthy athletes, leading to skewed results.
  • The more fat adapted you are, the more efficient you are at utilizing circulating ketones for fuel. This means, less in your system and a potential false negative test result.

Do you really need to measuring your ketones?

The short answer is no. It’s far more effective to develop intuition and use the day-to-day signs that are many of the benefits ketosis can provide. Read 5 Signs That You’re a Fat Adapted Athlete to find out more.

By all means, use measurements at the start to work how you respond, and how individual foods and meal choices impact your metabolism, but do not stress over your ketone levels. The irony here is that stress will limit ketone production, as it can cause glucose to be dumped in the bloodstream in a protective “fight-or-flight” mechanism. Read more on how stress impacts your metabolism here.

How do athletes benefit from ketosis?

Alright, time to get to the fun stuff. Want to know how ketosis can benefit your metabolic and performance goals? Here’s how:

  • Ketones offer an alternative fuel, especially beneficial for aerobic exercise

Using ketones to fuel aerobic activity results in the preservation of muscle glycogen for higher intensity. This is beneficial for athletes from CrossFitters to ultramarathoners, as metabolic flexibility should always be the goal – the ability to use multiple fuel sources well means you will never run out of fuel. You essentially become bonk-proof.

  • Ketones are a higher octane, better quality fuel

Ketones are simply more oxygen efficient and a cleaner fuel to burn. Sugars on the other hand, produce free radicals, and in excess will contribute to inflammation and accelerated aging. Ketones are anti-inflammatory, meaning you will recover faster.

  • Ketones prevent catabolism (protein breakdown)

Well trained athletes have up to 2000 calories of muscle glycogen available, but for extended exercise where these stores are depleted, an athlete can become catabolic in the absence of exogenous fuel. Burning ketones (and therefore sparing muscle) is extremely important and an essential part of exercise recovery.

  • Improved fat oxidation means a biased metabolic profile

Day-to-day you will experience:

  • Improved blood sugar control and satiety
  • Appetite control and a more efficient metabolism – you no longer need to snack every two hours
  • Craving control
  • Increased mental clarity
  • Avoidance of 3.30-itis
  • Weight management
  • Improved recovery
  • Injury prevention
  • Management of chronic disease.

In training and racing this will provide:

  • Stable energy levels
  • Decreased reliance on sports nutrition
  • Logistical ease on race day
  • Avoidance of gastro-intestinal (GI) distress
  • No more “hitting the wall”
  • Your athletic longevity.

What about ketone esters/exogenous ketones?

You may or may not have seen the increasing popularity of exogenous ketones (usually ketone esters) on the market. Here are some key points to consider:

  • From an evolutionary perspective, glucose and ketones work as a seesaw, meaning that ketones will be optimum in the absence of circulating glucose. How then, can it make sense to artificially increase ketones, without ensuring circulating glucose is low? More on this come.
  • There is no magic pill. As a society we need to stop looking for a quick fix, when the answer lies in real food, smart training and optimizing your metabolism.
  • They are great for appetite suppression, but your body still needs nutrients. Outside of experimenting with fasting, please ensure you are still consuming at least two decent sized meals per day (non-starchy vegetables, quality protein and healthy fats).
  • They are very expensive, with some companies charging over $5 per serve and more than $350 per month. Is it really worth the investment? Only you will be able to make that decision with trial and error.

From a performance stand point, please also consider:

  • Ketone esters improve efforts 20 minutes and beyond, meaning their positive impact is very duration specific. Due to the physiology of short and fast intervals, ketone esters simply aren’t necessary.
  • There is a potential that long term elevation of ketones may inhibit glycolysis. If you constantly have 4-5 mmol/L ketones, your body no longer needs to be good at oxidizing glucose. The end result? You lose your top end (i.e. you get slow).
  • And a final consideration, will longer term reliance on exogenous ketones blunt your innate natural production ability? I do not have the answer to this question, but I would certainly like to see strong positive scientific evidence before using ketone esters outside of a short-term cyclical scenario.

The reality is that you’re probably still going to try them, so we would rather you do it properly. If you are going to experiment with exogenous ketone esters, here’s how:

  • Start with JERF/LCHF

One particular multi-level marketing company (not mentioning any names), advises upwards of 200 grams of carbohydrates per day, which is enough to spike insulin levels in even the most metabolically healthy individual. To optimize ketone levels and mimic our evolutionary physiology, please ensure you get into nutritional ketosis first before adding in a purported magic pill (powder).

  • Buy from a reputable source

Multi-level marketing companies who create a proprietary blend and therefore do not need to disclose any ingredient concentration levels just smell fishy to me. Perfect Keto on the other hand, use 11.38g of BHB per serve, which is close to the highest amount of ketone bodies a human can effectively absorb at one time.

  • Use them smartly.

As discussed, using ketones is most suitable to fasted aerobic training. To minimize any impact on your metabolic potential, cycle them for two weeks at a time, and ensure you keep optimizing your metabolism naturally with the strategies discussed.

If you would like to know more on the science of exogenous ketones, I highly recommend the article My experience with exogenous ketones by Peter Attia.

 Do you have experience with nutritional ketosis or exogenous ketones? We’d love you to join in the conversation but please, as always, keep it research based and respectful.


  1. Maree

    Thanks for the information.

  2. Dyan

    Hi Steph,
    I have read comments about athletes switching to a ketogenic diet to benefit their performance and recovery, but am having trouble locating scientific evidence that this is true. This greatly surprised me! At best the dietary choice has be stated to not have had a detrimental effect on the athlete. I greatly appreciate and respect your expertise in this field, and am a subscriber to your podcast, to confirm that. Can you point me in the direction of scientific studies that have demonstrated the benefits of the LCHF practice?
    thank you for your time,


  3. Min Benstead

    Hello Dyan,
    There are a number of links within our article where you will find additional information regarding the benefits of a LCHF practice. Please also reference RFR episode 35 where Steph chatted with Peter Defty regarding his FASTER (Fat Adapted Substrate oxidation in Trained Elite Runners) study.
    Please also refer to Volek’s 2016 study here.
    It is important to remember that the bulk of the old research was conducted on carbohydrate burning athletes so ketosis would be detrimental pre-fat adaptation. 

  4. Dyan

    Ok, thanks for that. Have you heard of a ketone breath test machine? I’d be interested in checking my ketones after eating different foods.

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