Rough Stuff

In theory, fiber should be a runner's best friend. The nutrient, found in fruits, vegetables, beans, and whole grains, fills you up fast with few calories and keeps you feeling satisfied for a long time. On the road, however--as most runners will find out soon after eating a big bowl of bran cereal topped with a banana--fiber can also be a pain in the, um, gut.

If fiber causes runners to make so many unexpected pit stops, why bother with it at all? Because what makes it so hard on the digestive system is exactly what makes it so good for you. Fiber (your grandmother calls it "roughage") is an undigestible complex carbohydrate found in plants. It slows down the digestive process, which is good because your body receives a steadier supply of nutrients. There are two different types of fiber, and runners benefit from both. Water-soluble fiber, found mostly in fruits, vegetables, and beans, helps to lower cholesterol levels by transporting cholesterol to the liver, where it's destroyed. It can also help control blood-sugar levels. The other type--insoluble fiber, found mostly in whole grains--keeps the colon clean, which may help prevent colorectal cancer and other digestive disorders, such as diverticulitis. In fact, fiber is so good for you that the Institute of Medicine upped the daily-recommended intake to 25 grams per day for women and 38 grams per day for men (higher for men because of their higher calorie intake). That's a lot of beans and brown rice, and you're probably not getting enough. "Very few people eat enough fiber," says Lisa Dorfman, R.D., a spokesperson for the American Dietetic Association. "Most people don't even get 15 grams of fiber a day."

But they should, because fiber also helps keep your weight down. "The number of calories in fiber is very small, only one to two calories per gram," says Kristine Clark, Ph.D., director of sports nutrition at Penn State University. "Foods that are high in fiber fill you up on fewer calories, and they slow down the eating process because you actually have to chew them well." Fiber-rich foods not only take longer to eat, they also satisfy you longer. So if you're doing a 20-miler, eating complex carbohydrates that contain some fiber before you head out will provide you with the energy you need over the long haul.

For runners, however, the problem with fiber is that it can create a feeling of heaviness in the stomach and lower GI tract. Exercise only makes matters worse. So, how can runners reap all the benefits of fiber without experiencing the nutrient's nasty side effects? "Timing is everything," says Leslie Bonci, R.D., director of sports nutrition at the University of Pittsburgh Medical Center. Since it takes about two hours for the fiber you eat to leave the stomach and work its way into the intestine, you need to plan your intake accordingly. For instance, if you run in the morning, save the high-fiber cereal for after your run. Or if you plan to run at 6 p.m., don't have a bean burrito at 5. "If you usually run late in the day, it's a good idea to have most of your fiber at breakfast and lunch because it'll be digested by the time you head out," says Bonci. And Dorfman recommends limiting broccoli salads and lentil loafs, and trading multigrain breads and cereals for simpler carbs such as white-flour pasta and bagels a couple days before a big race, since race-day jitters and your higher-intensity effort will stress your digestive system.
Runners don't have to go totally fiber-free on the days they run. In a recent study at Penn State University, researchers had runners eat snacks containing about 100 calories and up to five grams of fiber 30 minutes before going for a 30-minute run (the choices were a Pria bar, a banana, or a serving of dried plums--a.k.a. prunes). "They expected to feel bloated and uncomfortable, but not one of them had any GI upset," says Clark, who was involved in the study.

The Penn State researchers concluded that the snacks were well tolerated because they contained only a moderate amount fiber, which means it's not only about when, but also about how much. "Try for five grams every time you eat, instead of going for 20 grams in one meal," says Bonci. If your current fiber intake falls drastically below what's recommended, take your time adding it to your diet. "It takes anywhere from a few weeks to several months for your body to adjust to the fiber you're eating," says Dorfman. Experts recommend adding no more than three to five grams of fiber per week. "Go about it gradually, the same way you would go about increasing your mileage," says Clark. For example, the first week, switch from white bread to whole wheat. The next week, eat an extra piece of fruit per day. The third week, mix a small amount of high-fiber cereal into your usual morning bowl. Your stomach will thank you.

The best way to include fiber in your diet is to have a little at each meal, says Leslie Bonci, author of the American Dietetic Association Guide to Better Digestion.
 

Sally Wadyka

Sally Wadyka is a freelance writer and editor based in Boulder, CO. She specializes in health, nutrition, fitness and beauty topics. When she's not writing, Sally can be found doing activities that feed her body, mind and soul—like hiking, trail running, rock climbing and skiing in the Rockies. Check her out at www.sallywadyka.com and on Twitter @SallyWadyka.