Why Bran Is Bad for IBS

Eating foods that contain bran can make irritable bowel syndrome (IBS) symptoms worse. If you have the condition, it's a good idea to make sure you get enough IBS-friendly sources of fiber in your diet. But, when you have IBS, bran fiber can lead to stomach upset and constipation.

What Is Bran?

Bran is a form of fiber derived from the hard outer layer of cereal grains like barley, corn, oats, rice, and wheat. Although bran can be derived from different cereal grains, products such as bran cereal and muffins are typically prepared with wheat bran.

In addition to being a source of potassium, iron, magnesium, and vitamin B6, a one-cup serving of wheat bran can provide 100% of your daily recommended intake of fiber.

Bran can be found in "all-bran" products and in products made with whole wheat flour. Whole wheat flour is comprised of the wheat germ (the inner part of the grain kernel), endosperm (the bulk of the grain kernel), and bran—all of which are milled together. The bran content aids in digestion and provides more nutritional components than refined flour.

IBS and Bran

Research shows that bran tends to make IBS symptoms worse.

Causes and Explanations

There is no definitive answer as to why bran can be problematic for people with IBS, although researchers have begun to offer hypotheses as to why this form of fiber can worsen symptoms.

One theory is that the hard bran shell is irritating to nerves in the lining of the intestines. As a condition characterized by the dysfunction of the brain-gut axis, IBS may be exacerbated by the physical strain placed on the enteric nervous system of the gut.

Another possibility is that wheat bran contains fructan, a fermentable carbohydrate that's one of several substances classified as a FODMAP. Eating a diet high in FODMAPs is believed to be linked to an increase in IBS symptoms.

An even simpler explanation is that a standard serving of wheat bran is simply too much for someone with IBS. As an insoluble fiber, wheat bran attracts water into the intestines, making stools softer and helping ease digestion. However, if you eat too much, it can increase gas production, leading to bloating and flatulence.

Given that one cup of wheat bran represents a full day's allowance of fiber, it is possible that a person with IBS may simply be eating more bran than they should. This may explain why some people with IBS are affected by bran and others aren't.

IBS-Friendly Fiber Alternatives

If wheat bran is causing you problems, there are other fiber alternatives you can consider.

Good sources of insoluble fiber include:

• Apples (unpeeled)
• Beans
• Blackberries
• Cauliflower
• Collard greens
• Green beans
• Green peas
• Kale
• Nuts
• Potatoes
• Prunes
• Spinach

You may be able to tolerate non-wheat sources of bran, particularly if constipation is an issue.

In terms of fiber supplements, psyllium (also known as an isphagula husk) may help alleviate IBS symptoms. Another option is ground flaxseed, which can help if constipation is the predominant symptom of your IBS.

A Word From Verywell

There is mounting evidence that the soluble fiber in fruits, vegetables, and legumes may be better tolerated in people with IBS than insoluble fiber. If you're unsure of which sources of fiber are best for you, consider meeting with a dietitian experienced with IBS to work out a dietary plan. Oftentimes, finding the best fit takes trial and error.

Irrespective of the type of fiber you consume, it is best to use a gradual approach when increasing your fiber intake to allow your body to adjust to the change.