Owner's Manual: Burn More, Run Faster
New study says you might be able to increase your on-the-go fuel
By Scott Boulbol
As featured in the November 2008 issue of Running Times Magazine
As a marathoner, you've probably developed and tweaked a refueling plan through years of trial and error. Eat a gel before the start, drink at every aid station, and take another gel every 10K, or something along those lines.
While your fine-tuned system might be working pretty well, new sports nutrition discoveries suggest you might want to tweak it again. The new focus is on what types of fuel to use -- not just when to fuel -- in order to achieve optimal racing performance.
Recent research finally proves two long-held assumptions in the athletic world: that consuming a combination of carbohydrates during prolonged exercise (more than two hours) results in higher absorption rates than a single source such as glucose; and that this increased absorption results in improved performance.
For years it has been known that consuming carbohydrates during endurance events is beneficial. But it was also commonly agreed upon that the body could absorb and process up to only 60 grams per hour from a single source of carbohydrates.
But there is a way to get the body to take in and burn more fuel -- and ultimately perform at a higher level. So says Dr. Asker Jeukendrup, professor of exercise metabolism at the University of Birmingham in England. In 2004 he proved for the first time that, by dramatically increasing intake and using various combinations of carbohydrates, the body can absorb up to 75 percent more than the accepted 60g max. But that study of increased absorption did not necessarily result in better performance.
Then, in February, Jeukendrup published his latest results in the journal Medicine & Science in Sports & Exercise. During a 3-hour stationary bike ride for several test subjects, the increase in absorption with a 2:1 ratio of glucose and fructose -- the combination with the best absorption rates in the earlier studies (though all combinations showed substantial increase) -- resulted in an increase in performance of up to 8 percent over just glucose, and an 18 percent increase over water alone. That new approach could be a big benefit to runners. For example, a 3-hour marathoner, in theory, could shave 14 minutes over 26.2 miles just by adjusting their refueling habits.
"This is the first study to show clear performance benefits of glucose plus fructose over and above the effects of glucose ingestion," Jeukendrup wrote in the original report. "These findings, in combination with previous studies in our lab, suggest that increased exogenous carbohydrate oxidation [when muscles utilize food-source carbs instead of their own stored glycogen] can be linked to increased performance."