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?
While the jury’s still out on athletes going high-fat all year round, periodising your nutrition might work better. Choose nutrients to match the demands of training. In winter, when workouts are less intense, choose quality fats. As intensity rises, up the carbs.
Note how the low-carb group not only burns more fat during exercise but at rest and recovery too.