I've been chatting with various running groups who're training for fall races, and I've heard variations on this question quite a few times:
"Can I make it through a half marathon (13.1 miles) or full marathon (26.2 miles) without eating anything and drinking only water?"
The short answer is yes, but it could be a pretty uncomfortable half marathon, and a BRUTALLY miserable marathon. And when I say brutally miserable, I’m talking about despondent feelings, crying, hallucinations, lead-feeling legs, falling down in a dramatic crumple, and/or completely ending your race.
It doesn’t make you weak to consume carbohydrate during your race. It makes you smart. It also makes it more likely you’ll have a fun time and less likely you’ll have a race day horror story to share.
To understand why we benefit from taking in carbs for races longer than 75-90 minutes, consider our body draws on two sources to create energy for exercise:
1. Carbohydrates (glucose stored in muscles as glycogen or in our blood from recently eaten carbohydrate)
2. Stored fat.
Imagine carbohydrate in your body as a tiny vial of rocket fuel: It’s your body’s most efficient and easy-to-use fuel, but you can only store a small amount of it. It powers hard efforts like sprinting and running up a hill, where you can’t catch your breath or talk comfortably (aka anaerobic exercise). Your brain also feeds off of that tiny vial of fuel.
When you think of the stored fat in your body, imagine a great big jug of fuel with a tight lid that requires a key for opening. And that key is oxygen. Even the skinniest of us has hours and hours of fat to burn. We burn fat during easy efforts, like walking (aka aerobic exercise). During easier effort, you’re breathing comfortably and getting oxygen to your cells to convert fat to fuel.
You’re not burning solely fat OR solely carbohydrate during your full or half marathon. You’re burning both, but depending on your intensity of effort, you're burning more of one than the other.
So now let’s imagine race day: Even with fully loaded carb stores, running at full tilt, it would only take an hour, two hours absolute max, to burn through that tiny vial of stored carbohydrate. When you’ve burned through the breakfast you ate, and emptied that vial of stored carbohydrate, your body and mind feel like they’re going to shut down, also referred to as bonking or hitting the wall. What is the best way to prevent running out of those stored carbs in a half or full marathon?
• Don’t go out at full tilt. By starting out at a more comfortable pace, you'll burn more fat (BIG jug!) and less carbohydrate (small vial). Go out too fast and you risk depleting that precious and tiny store of carbohydrate. Once you've hit the wall, it's not an easy process to bounce back
• Make sure that you have a proper breakfast on race day with a decent source of carbohydrates so you’ve topped off your carb stores
• Supplement on the course with carbohydrates, either in a drink, using sports nutrition products (the goo, gels, gummies, beans and the like) or for some very sensitive folks, with real food (dates, applesauce and other sugary, easy-to-digest foods). Depending on your size, 30-60 grams of carbohydrate an hour is the typical recommended range for carb consumption during a race longer than 75 minutes. That’s a sizable range, so experiment during your training. Don’t wait until race day to try out a drink or gel—that’s a rookie mistake with GI implications I don’t have room to address in this post!
UPDATE 9/1/16: I'm offering a discounted three-session Fueling Tune Up for half and full marathoners--more on that service here!