As an endurance athlete, should you be on a low carb, high fat diet? Getting the nutrition right is essential to ensuring you’ll perform at your best come race day, no matter your sport. In endurance based activity, it is particularly important, though it is the often forgotten part of these events. A common question of late revolves around should you be on a low carb, high fat diet for your endurance event?
This topic of ‘fat adaptation’ has been one of the most hotly discussed topics in sports nutrition recently, with many individuals shouting the benefits from the roof tops, or the finish lines. The question is, will a low carb, high fat diet help improve your performance?
Lets take a moment to move back to the science
Figure 1: Romijn JA. et al. (1993) Am J Physiol. 265(3 Pt 1):E380-91.
Figure 1 shows in a great pictorial form which type of fuel is being used for which type of activity. At low intensity exercise, free fatty acids in the blood are the main source of fuel, with some sugar from the blood, and fat from the muscles being used. At moderate intensity, mostly glycogen is used, along with fat from both the muscles and the blood and a little blood sugar. Glycogen is carbohydrate in it’s stored form. At higher intensities, glycogen is overwhelmingly the fuel of choice.
What does this actually mean?
At lower intensities, whilst more fat may be used as fuel, in an endurance event, you want to be going at your ‘maximum sustainable pace’, not a low intensity pace, for the duration of the event. Lower carb diets can result in limiting intensity of the workout. Why? Both carbohydrate and fat are broken down to a substance called ATP, for it to then be used as a fuel source. Carbohydrates require less oxygen for this process to occur than fat does. As a result, carbohydrate can be broken down more quickly, which is particularly important when exercising at higher intensities.
A research team from the AIS recently completed a study into LCHF, periodised carbohydrate intake (ie planning carbohydrate intake around training sessions), and high carbohydrate intake in elite race walkers. I can hear you thinking ‘walkers’. If you’ve never watched an elite walking race, I suggest you tune in. The qualifying time for the last Olympics was 84 minutes for a 20km race; that’s faster than many people can run! The key findings of the paper indicated that periodised and high carb groups had 5.3% and 6.6% better performance than baseline in a 10km test, whereas LCHF showed no improvement in performance.
Should I go low carb?
Reducing carbohydrate intake increases rate of fat use in physical activity. However, actual performance benefits are yet to be seen. If for some reason the individuals’ maximum sustainable pace for the overall time is not being achieved (for example pacing someone through a race at a slower pace than your maximum sustainable pace), it is likely more fat will be used for fuel in a session like this. However, in competition or training for competition, it is unlikely this will be the case. As such, carbohydrate availability is important.
Whilst it is important to include some fasted sessions, to help improve the body’s ability to use fat as a source of fuel, it is important to not do all sessions fasted, or all sessions with low carbohydrate availability. This can then actually make it harder for the body to utilise the carbohydrates when you go back to normal training, or using carbs in a race.
For some individuals with sensitive stomachs, modifying carbohydrate intake is also recommended. In some instances this may mean low carb, however impact on performance, and access to alternative products should also be taken into consideration.
Some people may wish to experiment with a LCHF style diet, which is entirely up to them. And yes, it does seem to work for some individuals. In most cases though, where performance is a goal, planning intake of carbs more strategically around training sessions is likely better for both health outcomes, and performance outcomes.
Chloe McLeod is an Accredited Practicing Dietitian and Sports Dietitian from Sydney. She is Director of the online course, The FODMAP Challenge, and Co-Owner of nutrition consulting company, Health & Performance Collective.