Fiber and Laxatives

Reviewed by: HU Medical Review Board | Last reviewed: May 2024 | Last updated: May 2024

After other conditions are ruled out and a diagnosis of irritable bowel syndrome (IBS) is made, treatments to manage the symptoms are generally categorized by gut-based strategies or central (brain-gut) strategies. Two of the common gut-based strategies are the use of fiber or laxatives to aid in the digestive process.1

Fiber for IBS with constipation

Dietary fiber is often suggested to people who have IBS with predominant constipation (IBS-C). Fiber is considered a bulking agent. When fiber is added to the diet, it provides more bulk and water retention in the stool, helping it pass through the intestines more easily. Fiber can be added by consuming more fiber-rich foods or by taking a fiber supplement orally. Fiber supplements can be made from natural ingredients like psyllium husk or synthetic ingredients like methylcellulose.1

Achieving relief from constipation with fiber generally requires high-dose therapy (20 to 30 g/day). This dosage is often linked to side effects like gas, bloating, and abdominal pain. Because these side effects are similar to IBS symptoms, fiber may not be an appropriate treatment for every person. As with many of the treatment options for IBS, you may need to try several options to determine what works best for you.2

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The American College of Gastroenterology recommends using soluble fiber rather than insoluble fiber. Soluble fiber is found in many foods, including oats, beans, and citrus fruits. Insoluble fiber is primarily found in wheat bran, vegetables, and whole grains.3,4

Laxatives for IBS with constipation

Laxatives are another option for people with IBS-C. There are 4 categories of laxatives.5

Bulk-forming laxatives

This category, which includes fiber supplements, relieves constipation by increasing the mass of feces. This stimulates the intestinal peristaltic movement. Bulk-forming laxatives, such as calcium polycarbophil (FiberCon®), have shown benefit over placebo in patients with IBS-C or IBS with mixed diarrhea and constipation (IBS-M).5,6

Osmotic laxatives

Osmotic laxatives increase the water held in the stool, which makes it easier to pass. This type of laxative is commonly found over the counter and includes magnesium products, lactulose syrup, sorbitol, and polyethylene glycol (Miralax®).2

Osmotic laxatives are commonly prescribed to people with IBS-C who have not had a positive response to fiber. Lactulose and sorbitol are effective for many people, but they may also cause more bloating and gas because these agents are metabolized by bacteria in the colon. Polyethylene glycol is less likely to cause these adverse effects.2

While osmotic laxatives are meant for only occasional constipation, they are generally safe for long-term use and regarded as preferable to stimulant laxatives.1

Stool softeners

Stool softeners may lubricate or soften the stool, making it easier to pass. Though they are safe and inexpensive, stool softeners are rarely helpful in the treatment of IBS-C. Plus, there are no randomized, controlled trials to study the use of stool softeners in people with IBS.6

Stimulant laxatives

Stimulant laxatives increase intestinal transit, but they may cause abdominal cramps. This type of laxative is generally used in acute cases of constipation. While they are effective, they should not be used as a long-term solution due to their potential for side effects. Plus, the body can become dependent on stimulant laxatives, requiring a higher dose to achieve the same effect.1,5

Other treatment options for IBS

Finding the right treatment combination to manage IBS symptoms can take time, as each person is unique and reacts differently to each treatment option. It can be frustrating to experience a trial-and-error process. Fortunately, there are several options to consider, including dietary changes, stress management, probiotics, and medications.

Before beginning treatment for IBS, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs.

Treatment results and side effects can vary from person to person. This treatment information is not meant to replace professional medical advice. Talk to your doctor about what to expect before starting and while taking any treatment.