Dietary Fiber for IBS-D, M, and C, Part 1

Whether you have IBS-D (diarrhea), IBS-C (constipation), or IBS-M (mixed), dietary fiber plays a crucial role in managing your symptoms! Fiber is a nutrient found naturally in different plant foods and is indigestible to the body.1

There are 2 types of fiber: soluble and insoluble.

Soluble fiber

Soluble fiber forms a gel as it passes along the intestinal tract, slowing down digestion. It improves satiety and keeps you fuller for longer, helping to limit grazing between meals.1 In forming this gel, soluble fiber absorbs fluid and acts as a bulking agent, binding the stool – an essential component in minimizing diarrhea for IBS-D.2 But, since some soluble fibers have fermentable properties, certain food options may not be appropriate with a low FODMAP diet.4 See part 2 of this article to guide you through low FODMAP for foods rich in soluble fiber.

Fiber supplements

Fiber supplements are often used in IBS. Before initiating a fiber supplement, work with a doctor and dietitian to address your diet. IBS is multifaceted, and fiber is just part of the equation. Factors such as hydration, exercise, beverages, food choices, and stress, all play a pertinent role in managing IBS. Supplements that are 100 percent soluble fiber are not easily fermented, helping with IBS-D and IBS-M.3 Also, bulk-forming laxatives like calcium polycarbophil absorb about 60 times their weight in water, making it helpful for both IBS-D and IBS-C. For IBS-C, constipation can often be addressed without a fiber supplement. Work with a gastrointestinal doctor and dietitian to help navigate your bowel movement history and make an appropriate fiber plan for your unique GI structure, medications, and health history.

Insoluble fiber

Insoluble fiber increases transit time through the intestines, ultimately providing a laxative effect.5,2 It can help alleviate constipation in IBS-C and is recommended to be consumed through food rather than supplements. While a food-first approach is always preferred, the fiber supplement noted above may be a helpful option for either regular or occasional use. How much fiber is needed?6

Adults <50 years old:

  • Adult males: 38 grams of fiber per day
  • Adult females: 25 grams of fiber per day

Adults >50 years old:

  • Adult males: 30 grams of fiber per day
  • Adult females: 21 grams of fiber per day

The low FODMAP diet and fiber

Don’t let FODMAPs get in the way of your fiber goals. FODMAP, also known as Fermentable Oligo-, Di- and Mono-saccharides And Polyols, are gas-producing carbohydrates that are not easily digested by the body. Adopting a low FODMAP diet has been shown to effectively alleviate IBS symptoms such as gas, bloating, constipation, diarrhea, and stomach pain. While following a low FODMAP diet is temporary, don’t let it get in the way of reaching your fiber goals. A little planning can go a long way.

The big picture on fiber and IBS

Whether you have IBS-D, IBS-C, or IBS-M, fiber is crucial in the diet. Soluble fiber benefits IBS-D patients more, while IBS-C patients benefit most from a mixture of both from food sources (in practice). However, most foods contain a combination of both types of fiber. Generally, soluble fiber is rich in barley, oats, nuts, seeds, beans, lentils, and some fruits and vegetables. Insoluble fiber is rich in wheat bran, whole grains, vegetables, and some fruits.5 Some people may find that different fiber-rich food exacerbate symptoms more than others, which is common! Work with a dietitian to determine which foods work best for you to help alleviate and/or prevent unwanted symptoms.

Aside from the IBS benefits of fiber, this mighty nutrient also reduces the risk of heart disease, diabetes, and diverticulitis.3 For a breakdown of soluble-rich versus insoluble-rich fiber foods, see Dietary Fiber for IBS-D, M, and C, Part 2.

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