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26.10.2014

Endurance athletes prepare better for races with a low-carb diet

Endurance athletes who are preparing for competitions may achieve better results if they cut their carbohydrate consumption right down, and replace the carbs with unsaturated fatty acids. Polish sports scientists drew this conclusion after performing a study in which 8 experienced male mountain bikers followed a low-carb ketogenic diet for four weeks.

Endurance sports paradox
There's something strange about the diet that most endurance athletes follow. While performing endurance sports the body burns mainly fat, but many endurance athletes eat huge amounts of carbohydrates (and often the kind that would give anyone with a bit of nutritional knowledge the heebie jeebies).

You'd expect that endurance athletes would be better off following a diet that provides most kcals in the form of fat – which would encourage their body to learn how to oxidise fats.

Study
That was the reasoning behind the Polish study, which was recently published in Nutrients. The researchers gave their subjects a standard diet for four weeks, and then put them on a ketogenic diet for another four weeks. The emphasis in the ketogenic diet was on unsaturated fatty acids. During both periods the subjects also followed a demanding training routine.

Cholesterol
For a start the ketogenic diet was good for the participants' heart and blood vessels. After four weeks on the low-carb diet the mountain bikers had significantly more 'good cholesterol' HDL in their blood. The effect on the 'bad cholesterol' LDL was not significant.

Slimmer
The low-carb diet also made the subjects slimmer. They lost no muscle mass whatsoever, but they did lose three kg body fat.

Muscle damage
After each diet period the researchers got the subjects to cycle for 90 minutes at moderate intensity, and at the end of that time to cycle to the point of exhaustion while the level of exertion was increased every minute.

The researchers monitored the concentration of the enzymes LDH and CK in the athletes' blood. The higher the concentration, the more muscle damage there is. From their measurements the Poles could see that the low-carb diet reduced muscle damage incurred during exertion.

Performance capacity
The low-carb diet boosted the body's oxygen uptake. After the ketogenic period the subjects' VO2max had risen.

On the other hand the subjects' maximum workload had decreased – at least, after the low-carb diet the athletes generated fewer Watts. From this the Poles concluded that a ketogenic diet is probably ideal preparation for competition, but that just before and during races endurance athletes are probably better off eating carbohydrates.

Conclusion
"High fat diets may be favorable for aerobic endurance athletes, during the preparatory season, when a high volume and low to moderate intensity of training loads predominate in the training process", the Poles write.

"High volume training on a ketogenic diet increases fat metabolism during exercise, reduces body mass and fat content and decreases post exercise muscle damage. Low carbohydrate ketogenic diets decrease the ability to perform high intensity work, due to decreased glycogen muscle stores and the lower activity of glycolytic enzymes, which is evidenced by a lower maximal work load during the last 15 min of the high intensity stage of the exercise protocol."

Source:
Nutrients. 2014 Jun 27;6(7):2493-508.

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