NEW YORK - A drink that provides energy for the body in the form of ketones, rather than sugar or fat, helped competitive cyclists ride farther during a half-hour ride, according to a new study.
Usually, energy for muscle cells comes from carbohydrates or fat, but when those fuels aren't available and the body is in "starvation mode" the liver will break down fat stores into ketones to use as fuel.
Ketosis, or production of ketones by the liver, "is a natural response to energy crisis and is of vital importance to us as it allows us to survive 'insults' such as starvation and even the first few hours after birth when fuel levels are low," said lead author Pete J Cox of the University of Oxford in the UK.
In the new study, researchers found that when ketones are provided in a drink, the body will use them for muscle fuel.
Ketone-powered workouts resulted in less lactate, a by-product of breaking down sugar that causes muscle cramps and soreness.
The researchers studied 39 high-level athletes, including former Olympic cyclists, to see how their metabolism changed after consuming the ketone drink and exercising.
Ketone uptake in the muscles increased as exercise got more intense.
In long-distance workouts, muscles used more ketones as fuel rather than breaking down glucose.
But in short bursts of high-intensity work, like sprints, muscles work anaerobically, without oxygen, and can't use ketones as fuel, since ketones can't be broken down without oxygen.
To examine athletic performance, eight athletes fasted overnight before completing two bicycle exercise trials of one-hour steady-state cycling and a 30-minute time trial.
For one trial, the cyclists drank a carbohydrate drink, and for another they had a drink with carbohydrates and ketones.
After the ketone drink, the cyclists travelled an average of 411m further in the half-hour time trial than after the carbohydrate drink, as reported in Cell Metabolism.
"Hopefully this finding will help many athletes realise that optimum fuelling for sport is not simply to ingest as much carbohydrate as possible before, during and after exercise," said Timothy Noakes of the University of Cape Town in South Africa, who was not part of the new study.
Most athletes will perform better by simply training more and eating fewer carbohydrates, Noakes told Reuters Health by email.
Safety studies have found no adverse effects of the ketone drink, but "taking excessive amounts of ketones from any source (ie more than the normal physiological levels our body is designed to cope with) can alter the acid balance of the body and this is not advisable," Cox said.
"Currently the drink is not commercially available, and is difficult to make even in a laboratory (patent protected), meaning it may be some time before this drink, or ones like it can be made readily available to the public," he said.
A University of Oxford company is now developing the ketone fuel to be commercially available later this year and the authors of the study may receive royalties from its sale.
It is still unclear whether the effects are greater in trained athletes, he said.
For the average athlete, the potential benefits of the drink are probably too small to be worth the effort, Noakes said.
Cox told Reuters Health by email that being able to switch the body to using ketones may be beneficial in certain settings, such as when patients need to sustain function in disease.