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Are low carb diets effective for sports performance?

It’s been five years since we spoke with Professor Louise Burke about low-carb diets for sports and we ask her if anything has changed.

Professor Louise Burke OAM PhD APD is Chair of Sports Nutrition at Australian Catholic University and has nearly 40 years of experience with elite athletes. She was Head of Sports Nutrition at the Australian Institute of Sport (AIS) from 1990 to 2018 and continues at the AIS as Chief of Nutrition Strategy. 

Has the low-carb, high-fat (LCHF) trend in sports nutrition fizzled out or is it still going strong? 

The most recent cycle of the LCHF diet in sports nutrition started in about 2012, so it’s definitely peaked and is on the downward trend but a decade is a long time in the life of a popular dietary idea.  This is the third time I’ve seen a wave of interest in high fat diets (in different versions and different sales pitches) in my dietetic career, but this time it’s been a more emphatic campaign. 

Why do you think this is?

I think we can blame the power and reach of modern social media for this. Any cycle usually starts with a surge of interest from strong influencers within both the science and lifestyle communities, and this time, both groups had their platforms amplified by social and lay media. The next phase involves a race between researchers to test out some of the claims and industry to monetise the interest - new books and education opportunities to spruik it, and new restaurant menus and food products to allow people to bring the diet to their own food environment.  While this promotes the interest and the uptake of the diet in the first instance, I think it eventually leads to its downfall.  Some of this is because the information about the diet and its marvellous benefits are often oversimplified and generalised.  Without the nuances, many people who take it up don’t do it properly or don’t have the characteristics to which it might be best targeted.  While the loudest voices proclaiming the benefits still make most of the noise, the growing experience is that it doesn’t achieve miracles.  The high-performance marathon runners and their sports science team discover, by trial and error or by reading the emerging studies, that there’s a sound biochemical/physiological roadblock to the use of fatty acids and ketone bodies to fuel an Olympic marathon. 

It’s been five years since we last interviewed you about whether the LCHF diet for sport was all hype, based on your published review at the time. Has anything changed?

(Last time Professor Burke said her review concluded that there is no new evidence that high fat diets improve performance across the range of sports in which athletes need to be able to work at high intensities/speeds/power outputs, even if it is only for a small but crucial part of the event.)   

Since our last review, we’ve done many complex studies with elite athletes to test out whether we’d missed any of the claimed benefits of the low carb high fat diet in our previous work.  The iteration of the diet that we studied in the early 2000s was carbohydrate-reduced rather than carbohydrate-restricted and ketogenic.  So, this time we followed the new dietary principles of < 50 g of carbs per day.  Our findings reinforced the concept that it is difficult to fuel high-intensity endurance events with fat, and that the ketone bodies don’t seem to provide a significant fuel source for the muscle.  

And we rediscovered one of the limitations to fat-adapted sports performance – that fat requires a greater amount of oxygen to produce energy/power/speed etc.  So that even if you can adapt your muscle to be a great fat oxidiser, there is a limit to the intensity of exercise that it can support due to the required oxygen supply.  Carbohydrate oxidation can produce energy more economically and has an oxygen-independent pathway.  We followed up by testing out lots of models to try to periodise LCHF with an additional fuel source to make up for its energy ceiling.  We restored glycogen, we provided carbs during exercise, and we experimented with ketone ester supplements.  But no strategy could reverse the impaired performance of sports conducted at ~80% maximal aerobic capacity and above associated with the LCHF diet. 

Are there any sports for which keto might be helpful?

The best opportunity for the keto diet in sports/exercise involves scenarios of prolonged low-moderate intensity exercise in which fat oxidation can meet the required rate of fuel production.  Even more so for situations or individuals who can’t consume carbohydrate during the event to sustain a muscle which prefers to burn carbohydrates – for example, self-supported treks or individuals who have gastrointestinal problems during exercise.

The Commonwealth Games are heading to Brisbane in 2032. Do you think there will still be debate about carbohydrates in sports performance then? What are your predictions for the future when it comes to the science of Sports nutrition? 

There will always be debates about carbs, and I hope there will always be evolution of our knowledge and practice.  I think the new frontiers will embrace more nuance – periodising nutrition according to specific workouts and differences in our unique needs and characteristics.  I hope there will be more research about the specific needs of female athletes – they are underrepresented in every theme of sports nutrition research.

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