Do Endurance Athletes Actually Need High-Carb Fueling?

There's a debate emerging in the endurance training world.

One camp says carbs are your friend, while the other says ditch carbs entirely in favor of fat as a preferred fuel.

The high-carb crew is seemingly well ahead, powered by the long held support of carbs for endurance training, along with many high-level endurance athletes who were pushing the limits on their ability to consume as many carbs as possible in their events and training.

One athlete, David Roche, who broke the trail record at the Leadville 100 last year, reported taking in 120g-140g of carbohydrates per hour.  I thought this Rich Roll podcast with David was an awesome look at his training theory.

And this article by Alex Hutchinson covers the surge in popularity of high-carb fueling even further.

However, a new study just dropped that adds some fuel to the fire for the low carb crew.  If you're interested, this blog by one of the researchers on the paper is probably easier to digest than the article itself.

They tested competitive triathletes on high-carb and low-carb diets, and here's what they found:

• Performance was the same. Both high-carb and low-carb groups performed equally well in a ride to exhaustion at 70% VO2 max, a moderate intensity at the upper end of a comfortable talking pace.

• Tiny carb doses worked wonders. An important twist on the study is that during the trial, they either gave them 10g/hour carb or a placebo drink. The carb intake boosted performance by 22% in both groups by eliminating exercise-induced hypoglycemia.

• Low-carb requires time. The low-carb athletes needed 4 weeks of adaptation to hit their stride—emphasizing the importance of patience when changing your diet.

The first point is that if you're pushing your performance for over an hour, either as part of training or at an event, then you should probably at least consume some carbohydrates.

But based on this study, it doesn't need to be much. According to Tim Noakes, one of the study's lead authors, you just need enough to cover the brain's glucose demand; otherwise, you "hit the wall."

More evidence is needed to answer whether more significant doses are beneficial. Until then, eat how you like and fuels you the best, and we'll have to see what shakes out of the research.

I personally would like to see similar studies but with some modifications.

1. Simulate the environment and intensity of a race. Based on the subjects' training level, I expected the time to exhaustion at a relatively moderate intensity to be much longer. Rather than examining the impact of carbs, this study may have just found the threshold that a human can spin on a bike in a lab.
2. What happens to performance when you give 20, 40, 60, or 80 grams of carbohydrates per hour?  And how do these needs differ between the elite endurance athlete, the age group competitor, and those there to just have fun.