Can Low Carb Improve Sports Performance?

Can a Low-Carb High-Fat Diet Improve Sports Performance?

As someone who participates in endurance events, you no doubt know how important it is to get your nutrition right (well… I hope you do if, you’ve been following these blogs!).

This topic of ‘fat adaptation’ has been one of the most hotly discussed topics in sports nutrition in recent times, with many individuals shouting the benefits from the roof tops, or the finish lines. But as a triathlete, should you be on a low carb, high fat (LCHF) diet? Will it help improve your performance?

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. As can be seen, 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 utilised.

At moderate intensity, mostly glycogen (aka stored carbohydrate) is used, along with fat from both the muscles and the blood and a little blood sugar. At higher intensities, glycogen is overwhelmingly the fuel of choice.

Low Carb Leads to Limited Intensity

Lower carb diets can result in limiting intensity of the workout. The main reason for this is because 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 out of the Australian Institute of Sport recently completed a study into LCHF, periodised carb intake, and high carb 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, however there was evidence of increased fat oxidation.

Should you 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 doing a training session with someone who is slower than you, or pacing them 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.

I’ve discussed in a previous post about incorporating fasted sessions into the day to day training program, in an effort to improve the body’s ability to utilise fat as a fuel source. It is important though to not do all sessions fasted, or all sessions with low carbohydrate availability, as 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.

Featured photo credit: Christine Cowen via / CC BY-ND

Chloe McLeod
Chloe McLeod
Chloe McLeod has had a keen interest in nutrition from a young age due to food intolerances as well as a realization about the important role food plays in an active lifestyle. She has a bachelor’s degree in Nutrition & Dietetics, a master’s degree in Public Health, has received Sports Dietetics training through the Australian Institute of Sport, and has earned qualifications for ISAK Level 1, and is a member of DAA, SDA, and PINES. She is a two-time marathoner, avid trail runner, and also enjoys staying active through snowboarding and Pilates.