Fiber and IBS

If you are living with irritable bowel syndrome (IBS), addressing your fiber intake is important and worthwhile before tackling more complex dietary strategies. Managing fiber alone can really help IBS symptoms. Eating enough fiber can help symptoms such as constipation, diarrhea, bloating, pain, and excess gas.¹

Fiber is really important for the health of your gut microbiome. Low-fiber diets contribute to health conditions such as inflammatory bowel disease, obesity, and type 2 diabetes.²

But while eating enough fiber can improve symptoms, fiber commonly makes symptoms worse in those with IBS. This can be due to a number of things, so in this article, I’m explaining what fiber is and things to consider when you have IBS.

What is fiber?

Fiber is a plant carbohydrate that escapes digestion, so it goes from your mouth down to your colon undigested. In your colon, it is digested or fermented by your microbiome. Your microbiome, an ecosystem of bacteria and living organisms, requires feeding. Fiber is the food it needs to thrive.²

Different types of fiber

The action of fiber depends on solubility, viscosity, and fermentation.³

Soluble (vs. insoluble) fiber

Solubility refers to how it dissolves in water. Soluble fiber dissolves in water and forms a gel. It is fermented by bacteria in the colon, which produce by-products such as short-chain fatty acids, which are known to have a range of health benefits.³

Viscous fiber

Viscous fiber is a type of soluble fiber in plant foods. Viscosity is often referred to as the thickness of a fluid. It slows the digestion of consumed nutrients and increases feelings of fullness. These effects are associated with reduced food intake and helpful for weight management.³

Where you’ll find soluble fiber: oats, barley, peas, beans, nuts, and fruits (such as apples and blueberries). Fiber in citrus fruits and legumes stimulates the growth of colonic flora, which increases fecal mass. Soluble fiber supplements include psyllium and guar gum.²

Insoluble fiber

Large and coarse insoluble fiber particles have a greater effect on stool bulking and increasing transit time. Examples of insoluble fiber include whole grains, wheat bran, rye, brown rice, carrots, cucumbers, and tomatoes. Supplements include lignin, cellulose, and resistant starch.⁴

Insoluble fiber can be beneficial for constipation, diverticulitis, hemorrhoids, and colon cancer prevention.⁴

Fermentable (vs. non-fermentable)

Fermentable fibers are easily processed by the gut microbiome. Fibers that are fermentable and can stimulate the growth and/or activity of beneficial gut bacteria are called prebiotic fibers. If not fermented, fiber retains a gel-forming effect in the colon and has a stool-normalizing effect. It is good for constipation or softening hard stool but also firming for diarrhea.²

Fermentation of fiber by the gut microbiome makes short-chain fatty acids (SCFAs), which provide energy and offer anti-inflammatory and immune effects to help guard against pathogens, metabolic effects, and many other health problems!²

Fiber and IBS

If you think fiber is triggering your IBS symptoms, here are a few points to consider:

• Remember that food should be chewed slowly, as digestion starts in the mouth.
• Increasing fiber intake may help IBS symptoms, but go slowly, as too much may worsen symptoms.
• Cooked vegetables are easier to digest than raw.
• Keep track with a food and symptom diary.
• Get support from a qualified nutritionist.

The bottom line: Fiber = microbiome food

Diet influences which types of gut bacteria flourish, retain, or disappear in humans throughout life. Low-dietary fiber diets result in low microbiome diversity, which means you probably don’t have the right types of bacteria to digest fiber.^2,3

Unfortunately, this can be the problem with diets created for IBS, such as the low FODMAP diet. While these diets are beneficial in reducing symptoms initially, they are not meant to be forever diets due to the impact they have on the microbiome.

When you eat low fiber for too long, you may not tolerate it when you first introduce it. From there, a slow journey of reintroducing fiber is needed to build back a microbiome that is able to digest more fiber.¹