Photo by Walk.Jog.Run.net
One of the first things I remember having many questions about when I first started running, is how to fuel for long runs and races. Admittedly, even after several years of training and racing, I still feel as if I am learning about fueling – there’s obviously a lot of trial and error. But one nutrition principle I always follow is one that has been vetted and supported by various nutrition experts, and yet it’s surprisingly unknown to many runners.
If you’re a marathoner (or half marathoner), you’re probably well aware that a high carbohydrate meal before an endurance race will help you go the distance without hitting the wall. What you might not know, is that eating your pre-race meal a couple of hours before race-time can actually hinder your efforts. Here’s how:
Studies have shown that high glycemic carbohydrates, or simple sugars, consumed at least 3 hours prior to an endurance event results in greater resistance to fatigue (versus when no meal is eaten at all). But when such a meal is consumed within two hours of commencing exercise, performance may actually decrease.
When food enters the body, serum insulin is released to help sugar/glucose (from the foods we eat) enter cells. Glucose is then broken down to provide energy. However, when it’s mostly high glycemic carbohydrates that enter the body, blood sugar spikes rapidly, causing excessive insulin production, and in turn causing a low blood glucose level.
Excessive insulin levels also inhibit the body’s ability to burn fat, and in endurance events, optimal fat utilization is desirable when glucose stores are eventually depleted.
Finally, high insulin levels push blood sugar into cells, forcing an increase in carbohydrate metabolism, which equals faster depletion of glycogen stores!
The best way to avoid all of the above is to eat at least 3 hours before races, allowing for insulin and blood glucose levels to return to normal. If eating 3 hours before a race seems impossible (due to an early morning start time for example), you can get away with consuming a small snack about 5 minutes before the race; one or two gel packets, or half an energy bar for example. In this case, glycogen depletion shouldn’t be a problem because you’ll already have started moving by the time blood sugar levels are elevated and insulin is released.
For a more thorough explanation, read this report by Hammer Fueling Expert, Steve Born.
Kraemer, William J., Fleck, Steven J., Deschenes, Michael R. Exercise Physiology: Integrating Theory And Application, 2012. Print.