Low Carb Training and Racing in Glycolytic Endurance Events

As a coach and athlete who’s focusing on carbohydrate restriction as a performance boost, way too often I get asked about why’s and how’s. Especially when it comes to glycolytic (sugar depended) high intensity efforts. Thus I decided to repost one of the articles covering one of my low-carb experiments and its application to obstacle races (by far one of the most intense endurance efforts).


Enter the world of low carb athlete.

Macronutrient ratios play a major role in a whole host of factors such as body composition, weight loss/gain, physical and mental performance, among others. So unquestionably, changing the ratio of any one macronutrient (carb, fat or protein) will have a strong effect, positive or negative. The fitness industry has known this for a long time, which is why we’ve seen fads like the low-fat diet movement (which now seems to be dying out), the bro-bodybuilder craze over protein consumption, high carb diets for the ultra (endurance) athletes and many more.

Every athlete will have their own preference, a tried and tested approach to diet that can best fuel their training and racing. But how can you find the best pick for you? Today we’ll cover one such approach – the ketogenic diet. It’s rather unconventional as it goes against the commonly spouted advice to carb up for endurance events, but we were keen to try it out. Read on to find out how the super-high fat, moderate protein and super-low carb keto approach affected my performance in a Spartan Race and my daily life.

Why low carb and ketosis?

I’m always looking to optimise my mental and physical performance, be it at work or while training. So I’ll gladly listen out for any hacks to help me stay sharp and better able to push past various (often self-imposed) limits. As a guide to incorporating keto into my daily routine I used the following materials: the well-known bio-hacker Dave Asprey’s book ‘The Bulletproof Diet’, fitness guru Ben Greenfield’s book ‘Beyond training’, various studies on fat-fuelled performance in cognitive and athletic fields available on PubMed, and quite a lot of ‘bro science’ articles across the web. These were a great primer to address some of my problem areas in order to achieve these personal goals:

  • Maintain existent physical performance (specifically, strength and endurance) without burning out during training or during a race
  • Heal/avoid various gut problems, effects of food intolerances and brain fog.

You can find out more on the subject by reading my previous articles here, here… and here.

The basic protocol

A few weeks ahead of my Stadium Spartan Sprint, I was fit on the outside, but inside I was struggling with gut problems and carb cravings. I then pushed my body into constant ketosis by putting into practice a modified keto protocol – the bulletproof diet. Here’s what the diet involved:

  • Twenty days of less than 25g a day (in contrast to over 300g net carbs a day, macro profile: Carb-Fat-Protein – 40-30-30. Daily calorie intake before experiment: approx. 3200 kcal, body: 187lbs 6’0)
  • New macro profile: 5-25-70. New fat sources include: grass-fed butter, MCT oils, fish/krill oil caps, coconut oil etc. Approx. calorie intake during the experiment: 4500 kcal. Every single meal to be soaked in saturated fats.
  • Same intensity workout plan consisting of: crossfit training several times a week, endurance and circuit training for extended amounts of time (1.5- 2h at a time), yoga and very few rest days
  • the 25g of carbs were to be delivered through gluten-free, histamine-free and organic vegetables and select fruit (coconut and pineapple are my personal favourites)
  • Daily journaling of: mood, cognitive abilities and training performance. For example, noting down run time for a mile, hunger level throughout the day or throughout training, any discomfort in the gut and other such irregularities. Weight was to be checked every week.

Training in ketosis

The transition to ketosis begins with 2-3 days of feeling terrible – your body is overstressed and in panic mode due to the lack of carbs. It feels as if you have the flu, which must be the typical man flu since none of the ladies ever complain about it. During this period your energy levels are pretty low, your body is burning the remaining glycogen storages and is starting to burn fat instead. As soon as those initial days were over, I could already feel some positive effects:

  • Extreme clarity and mental sharpness, feeling present and focused. Similar to the feeling you’d get from ingesting common neurotropics (smart drugs);
  • Suppressed appetite since stomaching all the fat is a challenge of its own;
  • Feeling light, because by this point some of the water weight maintained by carb consumption had flushed out.

Since I wanted to suss out the effects of keto on my training as well, I kept working out at the same intervals as before. This lead me to the following conclusions:

  • What I might have lacked in physical performance (due to glycogen depletion), I made up for with mental focus and extra dose of grit. These are attained thanks to the large amounts of slow release energy, enabling me to push myself further.
  • During high intensity workouts I would get dehydrated much sooner than during my old, carb-based training. E.g. during keto training of 2 hours with elevated heart rate I would consume around 2 litres of water. Previously, I could train at this same intensity without consuming any water.
  • Sweating more. I am a guy who would hardly break a sweat even during the most demanding exercises, but on the low-carb keto approach, I found myself sweating profusely, even during what I would consider easy warmups.

During the race

Just before my Stadium Spartan Race I fueled up on MCT oil and a modified version of Dave Asprey’s energy bites which contained approx. 70% of grass fed butter. This energy kicked in steadily, but admittedly a bit too late into the race. The first half of the 5k Sprint felt like a very tiring warmup (just like during the training sessions), and in the second half I felt more springy and excited. During training, this did not change much even when I tried to adjust the timing of fat consumption ahead of a workout.

Same as during training, the first signs of dehydration kicked in even before the race had kicked off. I had been drinking electrolyte-rich mineral water and flushing it out right away like a racing horse. To compound my trouble, the race course didn’t include any water stations. So almost an hour of running around and exerting myself was not at all pleasant with a desert-dry mouth and throat.

Final words

The goals I’d set at the beginning, I did achieve in spite of previously mentioned hardships like the constant dehydration. Performance-wise I definitely maintained my strength, agility and overall a-z endurance, even if it was not consistent and it kicked in later in the training session and the race. If you are looking for a very steady release of energy without the constant need to munch on sugar energy gels, you might want to try out racing on fat or in ketosis. Just make sure you know what the half life level of the energy to be released is before you max out.

During keto my gut felt better than ever. Although not feeling hungry might sound great, forcing yourself to chown down super fatty food gets old quickly. Believe me, consuming the total opposite of usually recommended macros was probably the hardest to-do in this experiment. The logistics (of carrying around butter and MCT oil to add to my meals) were a faff and drinking pure MCT oil on-the-go felt worse than that shot of alcohol when you know you’ve already drank too much. The thirst and dehydration are constant, so you’ll probably consume twice the usual amount of water.

Cycling ketosis at least bi-yearly allows me to drop fat quickly and get lighter for the races. Cannibalising some of my mass helps me to go further in a race. Overall, keto was a good experience, however I am not sure I will do it again during the racing season, since it is a tad harder to maintain and to always be prepared.