Keto diet may ramp up fat burning but comes at direct expense of elite performance

The ketogenic diet may turn elite Olympic athletes into fat-burning machines, but new ACU research has found it does not improve their endurance performance.

A new study from researchers at the Mary Mackillop Institute for Health Research, published in Medicine & Science in Sports & Exercise, found the low-carbohydrate, high-fat (LCHF) diet, also known as the ketogenic diet, impairs performance.

It showed elite racewalkers who consumed the keto diet in combination with ketone supplements were six per cent slower during a 10km race compared to athletes who consumed a high carbohydrate diet.

Lead researcher Dr Jamie Whitfield said the LCHF diet also increased the concentration of ketones – substances produced by the liver that the muscles and brain can use as fuel – in the blood.

The study follows on from the original 2016 Supernova study – led by ACU’s Professor Louise Burke, a world leading performance nutritionist and former head of sports nutrition at the Australian Institute of Sport – which found adherence to a LCHF diet turned elite racewalkers into fat-burning machines but compromised metabolic efficiency.

Professor Burke has been the team dietitian for five consecutive Australian Olympic teams, from 1996 to 2012 and is currently at the Tokyo 2020 Olympics.

Previous research had suggested ketones were a more efficient fuel compared to carbohydrates or fats, and that supplementing with ketones may improve performance.

However, this study found that taking a ketone supplement prior to exercise did not offset the loss of efficiency seen with the LCHF diet or improve performance.

The ketogenic or “keto” diet has become increasingly popular with athletes looking for a performance boost and people wanting to lose weight because of its ability to increase the rate of fat-burning during exercise, but there is long-standing debate over whether it enhances performance.

Dr Whitfield said when it comes to Olympic-level athletes, their performance suffered in the trade-off for ramping up fat-burning ability. Critically, he said athletes lost the ability to summon quick bursts of energy – crucial for those race-winning moves needed to cover changes of pace – when they needed it most.

“We’ve seen performances anywhere from four to six percent worse when consuming a LCHF diet whether it’s for three to five days or three to four weeks,” Dr Whitfield said.

“We have completed a series of studies looking at different dietary interventions with the ultimate goal of improving elite Olympic level athletic performance. This finding is very consistent with what we have shown in our earlier Supernova studies, so we think it is the LCHF diet that is the overwhelming negative here.”

Dr Whitfield said the LCHF diet throttles the body’s ability to use carbohydrates and to quickly move from one energy source to the other.

“We are not saying the keto diet is bad for all scenarios because that’s not what we have investigated,” he said.

“There is potentially a role for the keto diet or ketone supplements in other situations, but when it comes to high-intensity exercise on the Olympic program we haven’t seen a situation where it is beneficial.”

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