The IRONMAN Guide to Ketosis

March 12, 2017

Written by Megan Roberts, MSc, and Tommy Wood MD, PhD  

What if there was a way to:

  • Restore the boundless energy of your youth
  • Improve your body composition and mood
  • Eliminate the gas and bloating that plagues your every race
  • Fuel your races without Gatorade and sugary gels
  • AND regularly indulge in bacon, eggs, and butter???

Sounds too good to be true, right?

Well, the truth is that all of the above (and more) is achievable by embracing some diet and lifestyle changes. The crux of the secret - the ketogenic diet.

Perhaps you’ve heard of the ketogenic diet being touted for its weight loss efficacy. Or maybe you’ve heard it mentioned on Internet forums as the cure-all for everything from migraines to Alzheimer's to the pain in your little toe. But you? You’re an IRONMAN triathlete! You NEED carbohydrates to fuel your races, right??? Unfortunately, following that conventional sports nutrition advice has brought many desperate athletes to their knees, searching for an alternative when their health and training begin to suffer despite eating all those healthy whole grains.

This is the first in a series of articles that will introduce you to the ketogenic diet, specifically for the IRONMAN athlete. At the end of this article, you will have the basics to decide whether or not a ketogenic diet might be right for you.

What is ketosis?

Before answering the big question of how to get into ketosis, let’s define what ketosis actually is. Ketosis is a metabolic state in which you’re predominantly burning fat for fuel. Note that this is not the same as diabetic ketoacidosis, which is characterized by high levels of both ketones and sugar in the blood, particularly in patients with type 1 diabetes. In this case we’re talking about nutritional ketosis, which is a natural metabolic state involving a safe (and healthy) drop in blood glucose and insulin, and a rise in ketones [1]. Most people are highly dependent on carbohydrate, and switching to a fat-based metabolism has some huge benefits. This is particularly true for the endurance athlete.

Why ketosis for IRONMAN?

So now that you know what ketosis is, the next logical question is “why would I want to be in ketosis as an IRONMAN athlete?” Here is just a snapshot of how an IRONMAN athlete could benefit from ketosis:

  • Burn more fat for fuel at a given intensity
  • Lose weight and reach your optimal body composition
  • Tap into your own body fat stores during training and races… forget carrying hundreds of carbohydrate calories with you
  • Obtain a more stable blood sugar – no more bonking!
  • Recover faster from your workouts – keto is anti-inflammatory
  • Prevent the long-term health consequences from consuming copious amounts of processed carbs
  • Get rid of all that gas and bloating
  • Attain a higher degree of mental clarity, both on and off the race course
  • AND achieve this while racing just as fast as your carb-dependent opponents

Who doesn’t want all of the above, right? Now it’s time to dive into the details and learn just how to turn your body into a fat-burning machine.

How to get into ketosis


Changing the way you eat is the first and most important step to getting into fat-burning mode. Let’s talk macronutrients.

Fat: Eat fat. Lots and lots of healthy fat. Do not fear the fat!

Want to burn fat? You’ve gotta start eating more of it! Embracing fat will allow you to reach your energy needs since you’ll be drastically dropping your dietary carbohydrate load. Choose fats that are unprocessed and as close to nature as possible (i.e. no vegetable oils). Healthy options include extra virgin olive oil, coconut oil, grass-fed butter, ghee, avocados, nuts, seeds, egg yolks, and fats from healthy animals. Medium chain triglyceride (MCT) oil has a special place in a ketogenic diet, as (unlike other types of fats) it goes straight to the liver and can be rapidly used for production of ketones [2, 3]. Powdered MCT oil can be convenient and useful for ketogenic athletes on the go.

Protein: Moderate.

Many people make the mistake of thinking keto means low carb, high protein. Excess protein can actually reduce ketone levels which may be counter-productive. However, you also have to remember that eating enough quality protein is vital for muscle repair, recovery, and immunity. Self-experimentation with monitoring (see below) will allow you to find your unique protein threshold. A good starting place for protein is 1.2g/kg/day.

Carbs: Keto ≠ Zero Carb

Often ketogenic diets are misconstrued as zero carb diets. While it’s true that in order to get into ketosis you must drop your carbohydrate load significantly from what a typical IRONMAN triathlete consumes, athletes can get away with a lot more carbs than sedentary folk. Those who are fat-adapted and training hard can often consume upwards of 200 grams of carbs per day while in ketosis. The amount of carbohydrate you can get away with while staying in a fat-burning state is highly individual and dependent on training volume and intensity, as well as overall health (insulin sensitivity). Furthermore, when making the metabolic switch in the beginning, you may need to go lower-carb than when you’re fully fat-adapted down the road. Here are a few things to keep in mind when considering your carbohydrate load:

  • Opt for whole-food, unrefined carbohydrate sources (i.e. starchy vegetables such as sweet potatoes, white potatoes, winter squash, and fruit)
  • Strategically time carbs after intense training sessions
  • 2-a-days? Carbohydrate refeeds after your afternoon or evening workout and before bed can be especially helpful for sleep and recovery
  • Roughly 50 g/day (of net carbs) is a good place to start

Other diet considerations

  • Eat enough calories! It’s easy to under-eat while in ketosis (hence its efficacy for weight loss), but remember - athletes need fuel
  • Don’t forget plants! Bulletproof coffee is great, but don’t forget that colorful, non-starchy vegetables were put on the earth as a vehicle for fat
  • Sodium and electrolyte needs will increase on keto – use salt liberally
  • For race day fuel and long training sessions, think about MCT oil and MCT powder, amino acids, exogenous ketones, and slow carbohydrate sources like UCAN Superstarch

OK, now that we’ve covered diet basics, let’s talk training.

Transitioning to ketosis: how to optimize your IRONMAN training

Fasted morning workouts

Fasted training is an excellent way to prime your body to burn its fat stores instead of relying on calories from conventional sports nutrition. Start small. Even something as simple as a fasted morning walk is a good place to begin. Once you’re comfortable with that, hit the road, trail, or pool for a more focused fasted session.


Use it, but don’t abuse it! Take advantage of that morning cup of coffee. Caffeine is known to decrease the rate of perceived exertion during exercise and stimulate lipolysis (the breakdown of fats) [4, 5]. It can be a great way to enhance your fasted workouts when you’re feeling sluggish, but to get the most benefit, save it for the sessions where you really need a boost.

Slow down!

It’s important to train your body to burn fat using smart training strategies in conjunction with diet. Consider your transition to keto as an optimal time to build a strong aerobic base. The MAF Method is an excellent place to start.


While you should focus the majority of your training on building an aerobic, fat-burning engine, there is a time and place for intensity. Adding in some high intensity interval training will help you keep your top-end speed and remain metabolically flexible.


Dedicating some time every week to strength training will not only make you a better IRONMAN athlete, but will also help keep you injury-free and build the muscle mass and strength that is critical for longevity.


Be prepared to sacrifice short-term training performance for long-term race performance. For example, occasional “sleep low” strategies (skipping the post workout carbs after an evening session) can be beneficial for adaptations at the cellular level [6, 7]. Sure, you might feel slow during the next morning’s workout (enter caffeine), but the adaptations will be well worth the temporary sluggishness.

How do I know my ketogenic diet is working?

The number one way to tell if your new diet and training regimen are working is how you feel. Ask yourself:

  • Can I easily complete a fasted morning workout?
  • Have I abolished that 3pm slump?
  • Am I cognitively sharp throughout the day?
  • Am I no longer “hangry” between meals?

If you answered “yes” to the above, then you’re likely on the right track. You might also notice that your breath smells slightly fruity or metallic. This is acetone - another clue that you’re in ketosis.

But what if you like data and want hard numbers?? Enter: ketone testing. There are a few options as far as testing goes, each with its pros and cons:

Urine test strips


  • Inexpensive


  • Strips don’t provide an exact number
  • Results may be influenced by hydration levels
  • Urine ketones don’t necessarily reflect blood ketone levels
  • Urine ketone levels are higher when beginning a ketogenic diet, and decrease over time

Blood ketone meter


  • Measures beta-hydroxybutyrate (the major circulating ketone body) in the blood
  • Provides an exact number


  • Test strips are expensive

Breath ketone analyzer


  • One-time investment


  • Results can be highly variable depending on the context (i.e. after drinking alcohol)
  • Provides a range rather than an exact number
  • Breath acetone may not correlate with blood beta-hydroxybutyrate



  • Inexpensive
  • Useful for other health purposes


  • Measures blood glucose rather than ketones (but can provide some indirect information)

Remember, numbers may be helpful in the beginning to ensure that you’re on the right track, but testing can be cumbersome and unnecessary in the long-run.

When is the right time to start a ketogenic diet?

If any of the following scenarios sound like you, then now might just be the time to embark on the ketogenic lifestyle.

  • You’re tired of lacking energy or enthusiasm for your daily workouts and life in general
  • Your blood sugar is high (maybe even in the pre-diabetic range) despite the fact that you’re an athlete in excellent cardiovascular shape
  • You’re sick of having to plan your bike/run route to include multiple toilets
  • You’re experiencing symptoms of premature aging and want to increase your athletic longevity

Clearly, the above are some pretty compelling reasons for trying a ketogenic diet. But are there any contraindications to the diet?

Consider this: embarking on a ketogenic diet is a stress, especially in the beginning when you’re building the metabolic machinery to burn fat more efficiently. The dietary switch is the good kind of stress (hormesis), but must be seen in the context of your total stress “bucket”. The body perceives a hard training session the same as being stuck in traffic or drastically overhauling your diet. Be honest. Given the overall stress load in your life, is now the right time to begin keto? Depending on your unique situation, it may be best to take baby steps: switch to a less extreme, lower-carb, unprocessed whole food diet, fix your gut and any hormonal issues, and then begin to implement a ketogenic diet into your life.


You’ve lowered the carbs, upped the fat, and drastically slowed your training pace… But you’re STILL not in ketosis. What gives?!? Consider the following:

  • Are you overtraining and/or under-recovering?
  • How is the quantity and quality of your sleep?
  • How are your relationships outside of training?
  • How full is your stress bucket?
  • How do specific foods make you feel? For instance, dairy can be an issue for some.
  • Are you being impatient? Remember: keto-adaptation is a process. The mitochondrial adaptations that help you become an efficient fat-burner take time.

Overall, mindfulness is key. At the end of the day, if you have a gut feeling that now isn’t the right time, that’s perfectly okay. Ketosis will be there when you’re ready.

A common keto objection

Since you’ve read this far, maybe you’re sold on this keto thing. Or perhaps you’re a bit skeptical, especially if you have been hearing some of the common objections to the ketogenic diet, such as:

Does eating a ketogenic diet cause hormonal derangement?

Not inherently. Consider the following:

Calories. Some people who embark on a ketogenic diet may end up complaining about low thyroid or sex hormones, but association does not equal causation! Typically, the symptoms of low thyroid or sex hormones are simply the result of eating too few calories. Furthermore we know that nutrient availability is critical to proper thyroid hormone activation [7]. Since ketones can suppress appetite, it becomes critical that athletes pay close attention to eating enough calories from nutrient dense foods to both fuel activity and ensure hormonal balance.

Carbs. Apart from simply not eating enough calories, many keto athletes make the mistake of never ever consuming a starchy carbohydrate. They may even become “carbo-phobic” to some extent. But carbohydrates are not inherently bad given the appropriate context. While insulin is often vilified in low-carb circles, healthy insulin levels are necessary for regulation of thyroid hormone production [9]. As mentioned above, they can be strategically used to both enhance performance and ensure you’re sending the “I’m fed” signal to your brain.

Recovery. Overtraining by itself can cause symptoms of hormonal derangement [10]. And lack of recovery added on top of lack of calories is just a recipe for disaster. Consider turning “junk miles” into hikes with family and friends – this is an excellent way to spend time in nature while actively recovering and training your body to burn more fat.

Real-world case study

Theoretically, this whole ketosis thing sounds great…. But does it really work in practice?

It does. In fact, many triathletes have found a high-fat, ketogenic diet to improve their athletic longevity, performance, and health.

Case in point: Ben Greenfield. Ben trained for and completed IRONMAN Canada back in 2013 while eating a ketogenic diet. You can read more about the details of his experience on his blog. Since the race, he also participated in the FASTER study along with a handful of other keto-adapted athletes, demonstrating that extreme levels of fat oxidation during exercise are indeed possible and not detrimental to endurance performance [10]. Ben continues to perform feats of extreme endurance and strength whilst eating a high-fat diet.

Wrapping it up

To summarize the IRONMAN Guide to Ketosis:


Put simply, ketosis is the metabolic state of burning fat (instead of carbohydrate) for energy.


Fuel workouts with your own body fat stores, reap the health and recovery benefits of an anti-inflammatory diet, and experience less gastric distress during training and races.


Diet strategies: Eat lots of healthy fat, moderate protein, cut down and strategically time carbohydrates, and consume enough calories.

Training strategies: Slow down, take advantage of fasted workouts, and recover appropriately.

Practice mindfulness.

There you have it: a comprehensive IRONMAN guide to ketosis. If you’re ready to overhaul your training and health, this is the place to start! Gone will be the days of extreme fatigue and obsession with where you’ll get your next meal. In their place will be a newfound state of boundless energy, health, and freedom in both your training and everyday life.

Next steps

If you’re the ambitious and self-motivated type, simply use this guide to get started whenever you see fit. Share it with others so that more people can reap the benefits of the ketogenic lifestyle. Also, check out the 2016 Keto Summit for expert interviews and invaluable insight from the brightest minds in the community.

If, despite your best efforts, you are NOT getting the results you want, consider there may be something more complex going on. Many of the athletes we treat initially have problems getting into ketosis. When they get their lab work back, we are able to pinpoint and correct the issues preventing the desired performance gains.

Our clients are really, really well-informed - they know what they should be doing. Where they often get stuck is figuring out the sequence. Armed with precision tests and experience getting results for over 1,000 athletes like you, we will help you diagnose the situation, get the data and crack your unique performance code.

Tell us your story and we’ll see if we can help you reach your training goals. Book a free consultation, today!


1. Urbain, Paul, et al. "Impact of a 6-week non-energy-restricted ketogenic diet on physical fitness, body composition and biochemical parameters in healthy adults." Nutrition & Metabolism 14.1 (2017): 17.

2. Bach, Andrè C., and Virgen K. Babayan. “Medium-chain triglycerides: an update.” The American Journal of Clinical Nutrition 36.5 (1982): 950-962.

3. Courchesne-Loyer, Alexandre, et al. "Stimulation of mild, sustained ketonemia by medium-chain triacylglycerols in healthy humans: estimated potential contribution to brain energy metabolism." Nutrition 29.4 (2013): 635-640.

5. Astrup, A., et al. "Caffeine: a double-blind, placebo-controlled study of its thermogenic, metabolic, and cardiovascular effects in healthy volunteers." The American journal of clinical nutrition 51.5 (1990): 759-767.

6. Marquet, Laurie-Anne, et al. "Enhanced endurance performance by periodization of CHO intake:“sleep low” strategy." Med Sci Sports Exerc. doi 10 (2016).

7. Hawley, John A., and James P. Morton. "Ramping up the signal: promoting endurance training adaptation in skeletal muscle by nutritional manipulation." Clinical and Experimental Pharmacology and Physiology 41.8 (2014): 608-613.

8. Lartey, Lattoya J., et al. "Coupling between nutrient availability and thyroid hormone activation." Journal of Biological Chemistry 290.51 (2015): 30551-30561.

9. Ortiz, Lourdes, et al. "Transcriptional control of the forkhead thyroid transcription factor TTF-2 by thyrotropin, insulin, and insulin-like growth factor I." Journal of Biological Chemistry 272.37 (1997): 23334-23339.

10. Meeusen, Romain, et al. "Prevention, diagnosis, and treatment of the overtraining syndrome: joint consensus statement of the European College of Sport Science and the American College of Sports Medicine." Medicine and science in sports and exercise 45.1 (2013): 186-205.

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