Elite endurance athletes who eat very few carbohydrates burned more than twice as much fat as high-carb athletes during maximum exertion and prolonged exercise in a new study -- the highest fat-burning rates under these conditions ever seen by researchers.
The new study by Ohio state University researchers published in the journal Metabolism 2015, is the first to profile elite athletes habitually eating very low-carbohydrate diets, involved 20 ultra-endurance runners age 21-45 who were top competitors in running events of 50 kilometers (31 miles) or more
"These low-carb athletes were spectacular fat burners," said lead researcher professor Jeff Volek.. "Their peak fat burning and the amount of fat burned while running for three hours on a treadmill was dramatically higher than what the high-carb athletes were able to burn.
"This represents a real paradigm shift in sports nutrition, and I don't use that term lightly," he said. "Maybe we've got it all backwards and we need to re-examine everything we've been telling athletes for the last 40 years about loading up on carbs. Clearly it's not as straightforward as we used to think."
Ten low-carb athletes ate a diet consisting of 10 percent carbs, 19 percent protein and 70 percent fat, and another ten high-carb athletes got more than half their calories from carbs, with a ratio of 59 percent carbs, 14 percent protein and 25 percent fat. In all other respects, the athletes were similar: elite status, age, performance, training history and maximum oxygen capacity. "They all had the same engine, so to speak," Volek said.
It can take weeks or longer for the human body to fully adjust to a ketogenic diet, so the low-carb athletes in the study were eligible only if they had been restricting carbs for at least six months. Their average time on a ketogenic diet was 20 months.
"The goal was to characterize their metabolic response to a standardized exercise test," Volek said. "This is the first time we've had the opportunity to peek under the hood at what a long-term low-carb, fat-adapted athlete looks like."
Despite their low intake of carbs, these fat-burning athletes had normal muscle glycogen levels -- the storage form of carbohydrates -- at rest. They also broke down roughly the same level of glycogen as the high-carb runners during the long run, and synthesized the same amount of glycogen in their muscles during recovery as the high-carb athletes.
"The low-carb guys go beyond what you can achieve with good genetics and extensive training," Volek said. "The high-carb runners were very healthy, and were awesome fat burners by conventional standards -- yet their peak fat burning is less than half that of endurance athletes eating low-carb diets. This shows that we have far underestimated how much fat humans can burn. There is a large reserve capacity that can only be tapped if carbs are restricted.
The whole "Carb-Loading" approach that is adapted by many endurance athletes is not a healthy approach for long term health of the athlete in my opinion. If you engage in endurance sports It might be a good idea to try out a low-carb diet for a while - but remember to give adequate time-frame to keto-adapt in order to access the results