Excising carbs a futile exercise

New MacKillop research finds that low-carb, high fat diets may actually impair elite athlete performance.

Despite testimonials from some high-profile athletes and sports science professionals promoting the benefits of adopting a low carb high fat diet for endurance performance, new research from Mary Mackillop Institute for Health Research at Australian Catholic University and the Australian Institute of Sport, has revealed that a high fat, low carb diet can actually impair the performance of elite athletes.

Professor Louise Burke, Head of Sports Nutrition at the Australian Institute of Sport and Professorial Fellow at the Mary Mackillop Institute for Health Research, studied the performance of elite male race walkers, including a seven-time Olympic and World Championship medallist, over a three week period of intensified training.

The study was the first of its kind to examine the effect of a low carbohydrate, high-fat diet (LCHF) on metabolism and performance over the range of intensities at which endurance athletes train and compete.

In a crucial finding for competitive athletes and sports scientists, the study not only demonstrated how carbohydrates can improve exercise performance, it revealed that a LCHF diet can cause increased oxygen demand during exercise, reducing the efficiency by which athletes transfer metabolic power to mechanical power.

Professor Louise Burke said although it is clear that LCHF diets can increase the muscle’s ability to use fat as a fuel source, there was a lack of evidence to suggest that this improved sports performance, at least in endurance events in which there is still a need to work at high intensities, either for sustained periods or for the critical phases that determine competition success.

“Despite historical research confirming the benefit of strategies that promote carbohydrate as an exercise fuel, today’s published and social media tend to focus on popular theory about the benefits of switching the muscle’s fuel preference to its relatively greater stores of body fat.

“Contrary to popular belief that dropping carbs can help athletes to excel, our research found that athletes who consumed carbohydrate-targeted diets made performance gains after the training block, whereas the group who consumed the LCHF diet failed to improve their race times even though they had also become more aerobically fit.  While it’s clear a LCHF diet can change the muscle’s fuel use, the findings reiterate that further research is required to fully understand the extent to which LCHF can impact sports performance,” she said.


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