Fiber and Laxatives

Reviewed by: HU Medical Review Board | Last reviewed: March 2023

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 centrally (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 patients who have IBS with predominant constipation (IBS-C). Fiber is considered a bulking agent, and when it 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 of natural ingredients, like psyllium husk, or synthetic, in the case of methylcellulose.1

Achieving relief from constipation with fiber generally requires high-dose therapy (20-30 g/day), which is often associated with adverse effects such as gas, bloating, and abdominal pain. Because these adverse effects are similar to IBS symptoms, fiber may not be an appropriate treatment for every patient. As with many of the treatment options for IBS, patients may need to try several options to determine what works best for them.2

The American College of Gastroenterology recommends using soluble fiber, not 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

Another option for patients with IBS-C is laxatives. There are 4 categories of laxatives: bulk-forming, osmotic, stool softeners, and stimulant laxatives. Bulk-forming laxatives, which include fiber supplements, relieve constipation by increasing the mass of feces, which stimulates the intestinal peristaltic movement. Osmotic laxatives increase the water held in the stool, which makes it easier to pass. Stool softeners may lubricate or soften the stool, making them easier to pass. Stimulant laxatives increase intestinal transit but may cause abdominal cramps.5

Osmotic laxatives are commonly found over-the-counter and include magnesium products, lactulose syrup, sorbitol, and polyethylene glycol (Miralax). Osmotic laxatives are commonly prescribed to patients with IBS-C who have not had a positive response to fiber. Lactulose and sorbitol have been found to be effective for many patients, but they may also cause more bloating and gas because these agents are also metabolized by bacteria in the colon. Polyethylene glycol is less likely to cause these adverse effects.2

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

Bulk-forming laxatives, such as calcium polycarbophil (brand name FiberCon), have shown benefit over placebo in patients with IBS-C or IBS with mixed diarrhea and constipation (IBS-M).6

Stool softeners, although safe and inexpensive, are rarely helpful in the treatment of IBS-C, and there are no randomized, controlled trials to study the use of stool softeners in patients with IBS.6

Stimulant laxatives are 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. In addition, 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 patient is unique and reacts differently to each treatment option. It can be frustrating as patients 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.

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