By Roberta H. Anding, MS, Baylor College of Medicine and Texas Children’s Hospital

Edited by Kate Findley and proofread by Angela Shoemaker, The Great Courses Daily

You may have heard that fiber helps to treat constipation, but did you know it also works for diarrhea? Professor Anding explains.

How Fiber Treats Diarrhea

One benefit of a high-fiber diet is regulating your bowel function and easing constipation, as fiber adds bulk to your stools. Fiber can also be used to treat diarrhea.

Fiber can lessen or prevent diarrhea by solidifying loose and watery stools, depending on the type of fiber that you take in. If you take a water-soluble (gumming or gelling) fiber such as that found in oatmeal, it adds bulk to the stool, but it also holds water. 

“I worked for years in the HIV population—individuals who have AIDS—and one of the hallmarks of AIDS is chronic diarrhea,” Professor Anding said. “How do we blunt that diarrhea? How do we get that water to hold?”

They would use pectin, which—if you’re familiar with making jelly—is the water-soluble fiber that helps that fluid to gel. Professor Anding and her team would add the pectin to water, and when it got to the large intestine, it would help to hold some of that water in place. 

Diarrhea is the excessive loss of body fluid, and this technique helped to manipulate that gut physiology by manipulating the type of fiber that you could use to make sure you had optimal functioning. 

“I could blunt some of the fluid losses in my clients who had HIV disease by getting that water held in the large intestine,” Professor Anding said.

Fiber Precautions

In order to successfully treat diarrhea using water-soluble fibers, though, these fibers must have, as part of their matrix, adequate amounts of fluid. The primary role of the large intestine is to regulate fluid balance, so if you don’t have enough fluid, and you’re taking a water-soluble fiber, you can actually end up with an impaction—a worse-case scenario of too much fiber in the absence of fluid.

An impaction occurs when a hardened mass of stool is unable to pass through the colon. Therefore, if you’re consuming large amounts of fiber, you must stay properly hydrated. 

In fact, dehydration can often contribute to constipation. Keeping this precaution in mind, though, gelling agents such as pectin can effectively treat diarrhea.

The BRAT Diet

About 20 years ago, the BRAT diet was commonly used for the treatment of diarrhea. It consists of bananas, rice, apples, and—depending on whose research you read—tea or toast. This diet provides predominantly water-soluble fibers for the management of any kind of gastrointestinal disorder—in this case, diarrhea. 

The BRAT diet can also help to promote digestive health in other ways, such as lowering the risk of hemorrhoids. If you’re not straining to have a bowel movement, you’re much less likely to have hemorrhoids. 

Although there are many fiber supplements currently on the market, Professor Anding recommends that you eat a variety of high-fiber foods to prevent constipation and diarrhea. The American Dietetic Association is stressing to all consumers that the best benefits of fiber come from the food that we eat and not necessarily supplements.

Getting Children to Eat Fiber

For many people, though—particularly young children—eating a diet full of high-fiber foods may be challenging. Given the list of foods—which includes celery, beans, oatmeal, apples, and peas—there are going to be many children who reject those foods or prefer those foods in a more processed form. 

The processed forms of fiber don’t necessarily contain the same benefits as whole foods. For example, fiber benefits can be found in both applesauce and in apples, but the apple filling that is found in many energy bars and cereal bars is closer to a jelly. 

According to Professor Anding, this jelly filling is not a good source of fiber. Therefore, if you have a child in the family who doesn’t like apples, you should not swap out the apple for the apple filling in a toaster strudel.

However, you can offer applesauce as an alternative, as it is still an acceptable source of fiber. Similarly, you can offer more appealing versions of other high-fiber foods by adding nuts and raisins to oatmeal or making cauliflower “mashed potatoes.”

This article was edited by Kate Findley, Writer for The Great Courses Daily, and proofread by Angela Shoemaker, Proofreader and Copy Editor for The Great Courses Daily.

Professor Roberta H. Anding is a registered dietitian and Director of Sports Nutrition and a clinical dietitian at Baylor College of Medicine and Texas Children’s Hospital. She also teaches and lectures in the Baylor College of Medicine’s Department of Pediatrics, Section of Adolescent Medicine and Sports Medicine, and in the Department of Kinesiology at Rice University.