Many exercisers are plagued by gastrointestinal (GI) distress when they run or otherwise work out at moderate-to-high intensity, with symptoms such as bloating, gas, diarrhea, or abdominal pain. By some estimates, GI problems interfere with exercise performance or recovery in some 30 to 50 percent of endurance athletes—and as many as 90 percent of ultramarathoners.
One proposed dietary culprit behind the phenomenon is a class of carbohydrates given the acronym FODMAP, which refers to “fermentable oligosaccharides, disaccharides, monosaccharides, and polyols” (polyols are often referred to as “sugar alcohols” on the Nutrition Facts labels of packaged foods). These are short-chain carbohydrates found in varying amounts in a wide range of foods, including dairy products, legumes, wheat, rye, cashews and some other nuts, many fruits (like apricots, pears, apples, and watermelon) and vegetables (like cauliflower, onions, asparagus, and mushrooms), and honey and agave.
These carbohydrates are poorly absorbed in the intestines and subsequently digested by bacteria in the large intestine, where they produce gas. This gas, in turn, can cause flatulence and abdominal discomfort, including pain, cramping, nausea, or the urge to defecate. It’s no surprise that these uncomfortable symptoms can negatively impact an athlete’s performance.
To determine whether going on a low FODMAP diet—a diet increasingly used to manage irritable bowel syndrome (IBS)—might help people who experience GI issues during exercise, researchers conducted a study on 16 healthy recreational runners, ages 34 to 54, who had a history of at least mild exercise-related GI symptoms (but not a history of IBS). The participants ate either a low or a high FODMAP diet for a week, and then, after going back to their normal diet for a week, switched to the other diet intervention for another week.
Before and after each diet phase, the runners reported their digestive symptoms (for example, did they think bloating during exercise was noticeably different across the dietary periods?), as well as the duration, frequency, and intensity of their exercise during the week.
Published in the Journal of the International Society of Sports Nutrition earlier this year, the study found that when the runners followed the low FODMAP diet, most of them (69 percent) had reductions in symptoms, specifically abdominal pain and bloating, while most (75 percent) had no improvements or got worse when they ate the high FODMAP diet. Improvements were also noted in exercise frequency and intensity following the low FODMAP diet but not the high FODMAP diet.
How do exercise and food interact to affect the gut?
In brief, when you exercise at moderate-to-high intensity, less blood circulates through the GI tract, and this can lead to impairment in intestinal absorption. The result: More FODMAP food residues reach the large intestine.
Before adopting a low FODMAP diet to see if you might feel better during your runs or other workouts, here are some things to keep in mind: The study was small, the diet didn’t abate all GI symptoms (including diarrhea, flatulence, or urgency), and not everyone benefited. Also, the study included only recreational runners so it’s not known if other exercisers would benefit. And it’s unclear how long you must be on the diet to get benefits or how long the improvements would last once you stop the diet. (Because the diet is so restrictive and complicated, you wouldn’t want to be on it longer than necessary.)
Plus, a big problem for runners and other exercisers is that following a low FODMAP diet could result in a lower calorie and carbohydrate intake, which could lead to lethargy and fatigue and adversely affect performance. Carbs, in particular, are an important fuel in the body, especially when working out at high intensity.
Runners differ in how their guts react to specific foods. If you regularly experience exercise-related tummy troubles, you could keep a log of what you eat and your symptoms to try to find links between the two. Aside from high FODMAP foods, other foods and ingredients that commonly trigger GI problems are caffeine, alcohol, artificial sweeteners, soy, and high-fiber or high-fat foods. You might want to experiment with your diet—including trying a lactose-free or gluten-free diet—to see what works best for you.
For help with a low FODMAP diet, FODMAPeveryday.com is a good resource. It provides recipes certified by Monash University in Australia, where the diet was developed, along with other helpful information from IBS experts. An app developed at the Monash University includes a large database of foods rated by their FODMAP content.
This article first appeared in the UC Berkeley Wellness Letter.
Also see Mapping Out a Diet Plan for IBS.