Cultivating Metabolic Flexibility for Optimal Performance

Posted by Josh Gape on

Athletes, especially those who compete in sports that primarily rely on the anaerobic energy system (where steady power output is required from around 15 seconds to 2 minutes) often believe they need to eat high carb. This is true to an extent, in that carbs are needed to fuel this type of output and therefore should be consumed in adequate amounts around training sessions where the anaerobic zone is being worked. However, the majority of athletes I interact with are eating way more carbs than necessary to the detriment of their health and performance. 


Before we get in to the meat of this article, let’s lay out the energy systems at a high level for reference: 


  • ATP Energy System - relies on ATP stored in your cells and is utilised for maximum intensity efforts under 15 seconds

  • Anaerobic Energy System - relies on muscle glycogen (carbohydrates) to create ATP and is utilised for moderate intensity efforts of 15 seconds to 2 minutes

  • Aerobic Energy System - relies on muscle glycogen and free fatty acids (fat) and is utilised for lower intensity work for longer than 2 minutes


In reality all of these energy systems will be utilised when training or competing. However one will be predominant depending on the level of intensity required in the moment. 


Sports that rely heavily on the anaerobic energy system include; cross-fit, rugby and martial arts to name a few. For example, when a rugby player jogs at pace across the pitch to hit a ruck, then clears the ruck out, only to have to get back to their feet and make a tackle, they’ll predominantly be utilising this system. 


As stated above, the anaerobic energy system relies on muscle glycogen to create energy. Due to this, people often have the simplistic view of; ‘I compete in a sport which primarily utilises the anaerobic system, therefore I need to eat high carb every day.’ 


The body is very intelligent and will adapt to the fuel you’re providing it. Therefore if you are eating high carb every day, it’s going to rely on carbs as much as possible and down regulate your ability to utilise fat for fuel. Even as a predominately anaerobic athlete, this isn’t something you want because during those periods of lower intensity in training and games you’d be better off utilising fat for fuel and sparing your limited carbohydrate stores. 


The average person can store around 1,600 - 2,000 calories (400 - 500g) of glycogen in their muscles and liver. Comparably even lean individuals can store around 40,000 calories (4,444g) of fat. Let’s take a second to appreciate the difference here, our fat energy stores are at least 20 times greater than our carbohydrate stores. As a result, athletes who aren’t metabolically flexible (efficient at using both carbs and fat for fuel) often hit a wall during training or competition once they’ve burnt through their carbohydrate stores. However, if they were metabolically flexible this is way less likely to happen. This is because during periods of lower intensity their bodies will switch to using their huge fat stores, thus sparing their much smaller stores of carbohydrate for higher intensity periods when needed. 


The way I personally cultivate metabolic flexibility is through a Targeted Ketogenic Diet (TKD). This means that on non-training days I follow a Modified Ketogenic Diet (MKD) consisting of roughly 70% fat, 25% protein and 5% carbohydrates. However, on training days I ‘target’ additional carbs before, during or after training depending on the intensity. For example, if I’m doing a hypertrophy weights session in which I’ll be predominantly utilising my anaerobic energy system I’ll add an extra 50g of carbs prior to training. However, if I’m doing a lighter session consisting of some mobility and extras I may only have an extra 20g if that. 


Taking this approach means I’ll still be in ketosis most of the time and therefore will reap the associated benefits, which include; better appetite control, stable energy, increased cognition, etc. ⁣However, will also be able to optimally perform anaerobically, which wasn’t the case when I first started out on Keto and was just following a standard MKD approach. 


In addition to my anecdotal experience, research is now beginning to emerge demonstrating that a TKD approach creates a best of both worlds scenario. ⁣A study by Ryan Lowery compared performance on a standard ketogenic diet with a TKD and a carbohydrate rich diet when calories and protein were matched.⁣ Participants were instructed to complete exercise bouts on a Wingate bike. ⁣The people on a standard ketogenic diet had decreased power output during the initial bouts. However they performed better in the later rounds suggesting their fatigue resistance was much higher compared to the carbohydrate group.⁣ The TKD group performed best, matching the carbohydrate group on initial rounds and the standard ketogenic group on later rounds.


A number of high level athletes are starting to take notice of this. For example LeBron James, potentially the best basketball player of all time and TJ Dillashaw, former UFC Bantamweight Champion both openly utilise a TKD approach for optimal performance. 


In summary, carbohydrates are a great source of fuel but are being over relied upon in my opinion. As an athlete, you’d be much better off cycling down carbs and cycling up fat depending on your training schedule. This will encourage your body to be more metabolically flexible, which will enhance performance. Additionally, you’ll be able to capitalise on all the other benefits associated with being in ketosis as laid out above. 


To quote Charles Poloquin, one of the greatest strength and conditioning coaches ever to do it, ‘you need to earn your carbs.