Endurance athletes who restrict carbohydrates burn more than twice as much fat as high-carbohydrate athletes.’ The headline-grabbing study from Ohio University made news as ‘fat expert’ professor Jeff Volek proclaimed it the highest fat-burning rates he’d ever seen.


The study involved 20 top-end ultra-endurance runners. One group of 10 were habitual low-carb consumers, their daily diet consisting of 70% fat, 19% protein and just 11% carbs. The 10 high-carb athletes’ fuelling plan comprised 59% carbs, 25% fat and 14% protein.

Volek had the subjects run at 64% of maximal oxygen capacity for 3hrs to determine metabolic response. The low-carb group’s fat-burning rate was 2.3 times higher than the high-carb – 1.5g per minute compared to 0.67g.

“This represents a paradigm shift in sports nutrition,” says Volek. “Maybe we need to re-examine what we’ve been telling athletes about carb-loading for the last 40 years.”

Volek’s suggestion that endurance athletes switch from a high-carb to a high-fat diet to race stronger for longer isn’t confined to the labs. Cycling teams such as Tinkoff-Saxo and Team Sky are known for fuelling their winters on a high-fat diet… then reverting to a high-carb diet as the race season approaches.

The study revealed that during sub-maximal exercise, fat contributed to 88% of the low-carb group’s expenditure compared to 56% in the

high-carb group. Ultra-endurance athletes, such as recent Deca Worlds victor Dave Clamp, race at a lower intensity than a sprint- or Olympic-distance athlete. The shorter, faster distances demand a more maximal effort and there’s irrefutable proof that at high exercise intensities (over 80% of VO2max), carbohydrate is the main fuel regardless of diet. This might not be a problem. “Keto adaption [your metabolism shifting from relying on carbs to fat] increases fat oxidation across intensities,” says Volek. 

Volek’s findings also showed that the fat-burning group had normal muscle glycogen levels.

So what does all this mean for you?

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High fat isn’t the green light to pop out the Pringles. Look for good fats from foods such as avocados, nuts, coconut oil and pumpkin seeds.