In reading the research, I’ve found fueling for exercise to be a very personal thing. Some people can’t handle any food for hours before a run, whereas others run with full bellies. I have a finicky digestive system, and I’ll try to describe it to you without grossing you out.
I seem to have the worst of both worlds: If I don’t eat before a run, I bonk. “Bonk” is a highly technical term referring to a sudden feeling where you run out of gas due to low blood sugar and performance suffers. A lot. In the middle of nowhere I once begged a muffin from some hikers, and another time I got my arms scratched up raiding a roadside blackberry bush to get enough fuel to make it home.
If I eat too much, however, well… let’s just say I’ve been in a rush to find the nearest bathroom.
I finally solved my problem by following a simple rule: Eat little before a run and bring food. I know people are fond of things like energy gels and other expensive things you can buy at a running store, but I just use those Sunrype Fruit Source bars because they’re cheaper and do the job. I’d bring a banana instead, but that would get awfully mashed up in my pocket.
Over time I’ve figured out the right balance so that I can usually make it about 12-14K without needing food. I still bring it just in case, but most times don’t need it. A recent post at the New York Times Health Blog discourages eating while running (or doing other sports) for most people. The reason is simple: the majority of us won’t exercise long enough to need it.
In my marathon training going on longer distances I’ve had no choice but to bring both food and water, but if you never go further than 10K then chances are you can do it without needing to eat during the run. You may wish to bring food in case you do bonk, but my advice is to not actually eat it unless you feel as though you need it, because it can upset your stomach and may be adding calories you don’t actually need, which can interfere with weight loss if that’s your goal.
This is one of those cases of listening to your body. If you feel that eating during a run/cycle/swim etc. is necessary to keep going and keep performance up, then do it. However, don’t do it just because you think you should. Your body will let you know when it needs food.