Can a high-fiber diet help with IBS?

Whether a high-fiber diet helps IBS symptoms likely depends on a few factors, including the subtype of IBS (i.e., diarrhea-predominant, constipation-predominant, or mixed), the type of fiber consumed, and the person. There are two main types of fiber: soluble and insoluble. Insoluble and soluble fiber can be further characterized by their chain length, fermentability, and viscosity.^[1] Interestingly, different types of fiber can have very different effects on IBS symptoms. In general, experts recommend an increased intake of soluble fiber, but not insoluble fiber, for people with IBS.^[2][3] However, there are some caveats. For example, some sources of soluble fiber, such as fructans (e.g., inulin) and galactooligosaccharides, can aggravate IBS symptoms. These fibers are highly fermentable and may increase gas production and worsen bloating and feelings of fullness.^[4][5] These fiber types are found in foods like onions, garlic, asparagus, and legumes.^[6][7] In a low-FODMAP diet, these fibers (among other dietary components) are reduced and then slowly reintroduced, which may reduce symptoms of IBS, particularly in people with diarrhea-predominant IBS.^[8][9][10]
Psyllium is a soluble fiber with relatively low fermentability and high viscosity (gel-forming properties).^[11] Research suggests that supplementing with psyllium may reduce symptoms of IBS in all subtypes of IBS. However, psyllium fiber is difficult to come by naturally in foods and is usually taken as a dietary supplement.^[12][13] Insoluble fibers are commonly found in whole grains, fruits, and vegetables. They tend to undergo little fermentation and result in a low amount of gas production.^[1] Most studies on IBS have used wheat bran as a source of insoluble fiber, and results have consistently demonstrated no effect on symptoms of IBS.^[12][13]
The recommended intake for fiber is 25–38 grams per day.^[1] Research suggests that people with IBS tend to eat less fiber compared to people without IBS, which could indicate an avoidance of dietary triggers.^[14] Finding the right balance between consuming enough fiber and minimizing IBS symptoms can be a challenge. This often requires a personalized approach that can be aided by consulting a nutrition professional, like a dietitian or nutritionist.