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Diet and Ironman performance: appreciating the individual

It’s been a while since we last posted. The Plews has been training the house down to have his crack in Kona, while I’ve had my head down in my new initiative called HIIT Science, which teaches the science and application of high-intensity interval training (HIIT). If you’re a coach, athlete or sport scientist, you’ll want to check it out. #PlewsandProf are your lecturers for triathlon of course.

I needed to take a pause in that project for now to describe my experience as the coach involved with a recently published case study (9) in the International Journal of Sport Nutrition and Exercise Metabolism by friend and colleague, Iñigo Mujika.

As you can read, Iñigo does well to describe the challenges faced by a high-level triathlete I had the privilege of coaching for a short time.


But before venturing into that story, now may be a great time to appreciate a relevant topic doing the rounds at the moment, called Dunning-Kruger effect, depicted in Figure 1.

Fig 1. The cognitive bias of illusory superiority described by social psychologists David Dunning and Justin Kruger.

The Dunning-Kruger effect is an important concept for all of us to appreciate. It describes our evolution of both confidence and knowledge and understanding in any field as we pass through time, as we age, and gather more experience. In the beginning, we might start on the left side of the graph. This could mean the stage you reach upon finishing a coaching course, a degree or diploma in nutrition or sport science, publishing a manuscript in a journal, or whatever level of experience you feel you have gained in your life. Once the stage of competence is reached, we might be labeled an expert! Confidence is high. But continue moving towards the middle of the graph and beginning to work in the field, things don’t necessarily go as might be expected. Confidence is diminished as part of the natural process of testing hypotheses and not getting expected results. The important point I want to make relates to the famous related quote by Bertrand Russell, which states that:

“the fundamental cause of trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.”

Thus, when you view comments on social media, etc., consider how they appear to line up on the graph. Are they full of confidence or are they a bit more open? I’ll put my own hand up and say that I’ve been on the Dunning-Kruger journey, and at times may have wrongly displayed the cocksure behaviour associated with the left side of the graph. But I too have progressed towards the middle of the graph. There’s more to this than I thought.

If this resonates with you, it might be worth having a listen to Sam Harris’ recent podcast on the topic with Jonathan Haidt, discussing how social media is crushing nuance. That certainly appears to be the case in this sometimes-frightening arena of nutritional debate over a few macronutrients as they relate to exercise performance. So as you read this, I hope you’ll be open to considering all sides of the situation, displaying what Martin Buchheit describes as Type 3 behaviour. The post leads us to conclude that nutrition, as it relates to athletic performance, is extremely personal, individual and complicated.

My history

A quick bit of background on me so that my biases are clear. I was a long time ‘semi-pro’ triathlete from the 90’s, lived and raced the high carb life, and formerly designed an app that calculated the optimal carbohydrate proportions for Ironman racing called never-bonk. Shortly after designing the app, I found myself getting a bit too fat and going slower. Giving LCHF a try as it gained mainstream popularity, low and behold, I lost 10 kg, felt better, got healthier, and went sub-10 at IM NZ, my fastest race ever as a 43-year old. I had an experience that the published science I had read and believed did not support.

Since then, together with The Plews, we have helped a number of athletes through similar journeys through a combination of both training and nutritional advice. Typically, the scenario involves talented athletes that approach us with the general complaint of a diminishing performance as they age; the performance hampered by gastrointestinal discomfort issues in the back half of these long races. With patience and persistence over a ~2-month time course, issues tend to be ameliorated after reverting to the LCHF diet. Phil Maffetone and I describe the general procedure here in this published case study (7), with adjusted carbohydrate for key sessions as described (4, 5, 13).

We have written more on these successful case studies in a previous blog post. These transitions have been extremely successful for some of our athletes, and we are proud to be associated with 7% of the pro male field lining up in Kona this year.

A notable absence from the mix

Now to the important case that didn’t go well. Many of you will know or know of Eneko Llanos. Eneko is both an exceptional athlete and wonderful human being, as demonstrated through his willingness to consent for both Iñigo to write the published case study (9), as well as for me to write this blog post. At the end of the day, all of us mentioned in the article, whichever side of the fence their biases may sit on, simply hope the work contributes to helping others learn, consider different options, and solve their own individual performance puzzles.

I met Eneko in Kona in 2016 after a disappointing performance for him, where he described the typical debilitating GI symptoms he was experiencing. The gut issues were getting worse and worse for him the more he raced towards his 40’s, becoming so bad that they would force him to stop and walk from about 20k of the marathon. To be clear, there was no real performance issue from a physical output standpoint – it was the crippling pain in the gut that had become the limiting factor for Eneko. These are well described in the scientific literature (10). Carbs around exercise help the performance, but their use in high amounts additionally increase gut issues (gas, bloating, pain, etc) (10).

So if we’re looking to optimize Ironman performance, we likely all have some individual level of balance between getting too much of a good thing that enhances performance, and reaching a saturation point where too much creates these debilitating gut issues (10). Where that level sits for everyone seems highly individual. Coming to me, Eneko had reached his limit. On the one hand, he needed the carbs to perform, but at the same time, they were killing his race.

From there, I described the strategy we would attempt, and we immediately went on our way of trying to adapt to the LCHF diet. The only challenge thrown my way was that Eneko was a lacto-ovo vegetarian. So, a modified version of the LCHF diet we typically use was going to be required. This limits food selections. Eggs, high fat dairy, olive oil and avocado, alongside low carb veg and nuts become diet staples. At this point it may be helpful to read Iñigo’s case report (9), of which I was a random reviewer of the work, openly revealing my identity as Eneko’s former coach to associate editor Trent Stellingwerff and Iñigo in the process.

To cut a long story short, it was a challenging year for athlete and coach, and we parted ways wishing each other well following his second-place at Ironman Austria, where prior to this race he had reverted back to his normal high-CHO vegetarian diet for about a month. While there was the occasional glimpse of good performances in training during the LCHF period, in general it can be one described as very difficult, with mood low, and power/performance diminished, as described in the report (9). Clearly things were not working as they had for the others.


We have to continue to ask questions.

  • Why have we seen successful outcomes for the former athletes described, but not for Eneko? As Iñigo writes: “Whether his vegetarianism, his age and/or being accustomed to a HCHO diet over his entire triathlon career affected to some degree the potential effects of LCHF on his ultra-endurance performance and subjective wellbeing remains to be elucidated”. Dietary records suggest that micronutrients and protein quantities were similar on high vs. low carb vegetarian diets (9).

  • Was a vegetarian diet itself potentially contributing? There are reports that a vegetarian diet (irrespective of high vs low carb) may be lacking in various micronutrients that include B vitamins, zinc and fatty acid composition. Jan Frodeno is reported to have switched to a vegetarian diet last year before his Kona lead up. Was this a contributor to last year’s challenges over the longer distance?

  • Some have suggested that fat oxidation rates following fat adaptation from the LCHF diet are insufficient for fueling the high exercise intensities needed for performance, but these disregard a number of assumptions about fat oxidation rates (3), and the common errors in calculation.

  • As shown in Figure 2 from Maunder et al. (8), fat oxidation rates can range from 1.1 to 1.5 g/min in elites (8, 12), which become more than sufficient to enable Ironman performance with supplementation of only moderate levels of carbohydrate consumption throughout the event.

  • Trent Stellingwerff, who kindly reviewed the blog, reminded me that an enzyme in the muscle (PDH) responsible for glucose flux in the muscle is downregulated with dietary shifts towards fat (11), which may decrease economy (or increase VO2) at a given/set external load (speed/wattage) when fat adapted (1, 2); carbohydrate oxidation being slightly more efficient at producing ATP over fat (6). However, this idea is not without challenge (14), and we just don’t know the situation in chronically fat-adapted athletes, who obviously still go very well using their strategy.

We can all speculate, but at the end of the day, all we can say is that this strategy was not successful for Eneko in his context. Of course, we wish him well as he strives to solve his performance puzzle. We want to know the solution.

The individual

The final note we should leave on is that these are all n = 1 case studies. And while a vegetarian LCHF strategy did not work for Eneko, the omnivore version of the LCHF diet has worked for others. Kyle Buckingham, for example, described his success with the intervention.

As has Jan Van Berkel, recent winner of Ironman Zürich:

“LCHF worked for me. I believe it’s about doing it properly and sticking to it. I had to re-learn how to cook, how to shop for food and how to think about nutrition. In 2016, I changed my training and my nutrition towards LCHF. I feel it helped me improve my marathon time in Ironman by over 11min, go 7h48 to be the fastest Swiss Ironman athlete ever, winning Ironman Zürich with a new course record by 4min. Importantly, LCHF doesn’t mean I’m racing with guacamole and olive oil in my bike bottles.“

And of course, from The Plews himself, he believes this has been instrumental in taking him from a 9:22 to an 8:35 athlete over a five-year period.

But we really need to finish the post with the other end of the spectrum so that both sides of this debate are appreciated. After Iñigo published the case study, he received the following message from another world class podium-level endurance athlete. She writes to him:

Hi Iñigo,

I was on LCHF for one season. I still ate carbs before and during my training and racing. The biggest changes I made were:

  • a lot more meat and cheese

  • cutting grains out of my diet (So when I did eat carbs it was sweet potatoes, potatoes, squash, fruit)

Initially, I lost weight and performance seemed to go up. But when it went down, it was awful. I stopped menstruating (something that had never happened prior), my hormones were all messed up, and my doctor couldn’t say why. Initially I thought it would just take my body a couple months to adjust, but after several months, no menstruation, messed up hormones, gaining weight, and dropping performance, I stopped the diet. I too was experiencing feelings of depression, which was very unusual for me. It took several months of my normal diet for my menstruation to resume. I know some people swear by it, but LCHF was terrible for me.

Where to from here?

Figure 3. The individual and opposite glucose responses to the same foods in different individuals (15).

For now, only that we are all individuals. As Trent reminds us, the individual variability to food, in terms of both the glucose response (see figure 3) (15), and level of fat adaptation attained (8), is off the charts. Thus, the nutrition rabbit hole might go down as deep as our DNA, with innumerable confounding branches impacting along the way.

All we can say really is that if you want to optimize your diet in relation to exercise performance, you need to figure out what works for you. LCHF is clearly working for some at the pointy end, but not for others. We recognize that there will be every other combination of experience in between, because diet is personal and individual, and is affected not only by what’s put in your mouth, but external circumstances such as stress, sleep and psychology. It’s up to the athlete and coach/practitioner to work together, experiment, and in doing so, learn what works for them. As Iñigo concludes in his article (9), until carefully controlled trials investigating the effects of different diets on the performance of elite endurance and ultra-endurance athletes become available, the careful testimonials of athletes, such as the world class triathletes currently described, can add to our knowledge of how such dietary strategies may be applied in the individual.


  1. Burke LM, Ross ML, Garvican-Lewis LA, Welvaert M, Heikura IA, Forbes SG, Mirtschin JG, Cato LE, Strobel N, Sharma AP, and Hawley JA. Low carbohydrate, high fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol 595: 2785-2807, 2017.

  2. Hawley JA and Leckey JJ. Carbohydrate Dependence During Prolonged, Intense Endurance Exercise. Sports Med 45 Suppl 1: S5-12, 2015.

  3. Hetlelid KJ, Plews DJ, Herold E, Laursen PB, and Sieler S. Rethinking the role of fat oxidation: substrate utilisation during high-intensity interval training in well-trained and recreationally trained runners. BMJ Open Sport & Exercise Medicine 1, 2015.

  4. Impey SG, Hammond KM, Shepherd SO, Sharples AP, Stewart C, Limb M, Smith K, Philp A, Jeromson S, Hamilton DL, Close GL, and Morton JP. Fuel for the work required: a practical approach to amalgamating train-low paradigms for endurance athletes. Physiological reports 4, 2016.

  5. Impey SG, Hearris MA, Hammond KM, Bartlett JD, Louis J, Close GL, and Morton JP. Fuel for the Work Required: A Theoretical Framework for Carbohydrate Periodization and the Glycogen Threshold Hypothesis. Sports Med, 2018.

  6. Krogh A, Lindhard J, Liljestrand G, and Gad-Andresen K. The relative value of fat and carbohydrate as sources of muscular energy. With appendices on the correlation between standard metabolism and the respiratory quotient during rest and work. Biochem J 14: 290-363, 1920.

  7. Maffetone PB and Laursen PB. Reductions in training load and dietary carbohydrates help restore health and improve performance in an Ironman triathlete. . International Journal of Sports Science & Coaching 12: 514–519, 2017.

  8. Maunder E, Kilding AE, and Plews DJ. Substrate Metabolism During Ironman Triathlon: Different Horses on the Same Courses. Sports Med 48: 2219-2226, 2018.

  9. Mujika I. Case Study: Long-Term Low Carbohydrate, High Fat Diet Impairs Performance and Subjective Wellbeing in a World-Class Vegetarian Long-Distance Triathlete. Int J Sport Nutr Exerc Metab: 1-19, 2018.

  10. Pfeiffer B, Stellingwerff T, Hodgson AB, Randell R, Pottgen K, Res P, and Jeukendrup AE. Nutritional Intake and Gastrointestinal Problems during Competitive Endurance Events. Medicine and Science in Sports and Exercise, 2011.

  11. Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, and Burke LM. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. American journal of physiology Endocrinology and metabolism 290: E380-388, 2006.

  12. Webster CC and Smith JA. Comment on: Substrate Metabolism During Ironman Triathlon: Different Horses on the Same Courses. Sports Med 48: 2421-2422, 2018.

  13. Webster CC, Swart J, Noakes TD, and Smith JA. A Carbohydrate Ingestion Intervention in an Elite Athlete Who Follows a Low-Carbohydrate High-Fat Diet. Int J Sports Physiol Perform 13: 957-960, 2018.

  14. Wood T. Lost Metabolic Machinery During Ketosis? Depends Where You Are Looking. Strength and conditioning journal 39: 94-95, 2017.

  15. Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, Ben-Yacov O, Lador D, Avnit-Sagi T, Lotan-Pompan M, Suez J, Mahdi JA, Matot E, Malka G, Kosower N, Rein M, Zilberman-Schapira G, Dohnalova L, Pevsner-Fischer M, Bikovsky R, Halpern Z, Elinav E, and Segal E. Personalized Nutrition by Prediction of Glycemic Responses. Cell 163: 1079-1094, 2015.

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