Why Bran Is Bad for IBS

In an all-too-common scenario, you go to the doctor complaining of abdominal pain and a change in your bowel habits. Your doctor offers a diagnosis of irritable bowel syndrome (IBS) and recommends that you increase your intake of fiber. You then go to the store and buy yourself a box of bran cereal.

However, after a few days, you realize that your symptoms have worsened and conclude fiber is "bad" for you. What you not realize is that bran—not fiber in general—can cause trigger symptoms independent of IBS and make IBS symptoms worse.

Bowls of oat bran and oat bran flakes
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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. To better understand what bran is, think of brown rice versus white rice. With brown rice, the bran layer remains intact, while white rice has had its bran layer removed.

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 an excellent source of potassium, iron, magnesium, and vitamin B6, wheat bran can provide 100% of your daily recommended intake of fiber with just a one-cup serving.

Bran can be found in "all-bran" products but also in those 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. It is considered "healthier" because the bran content aids in digestion and provides greater nutrition than refined flour.

IBS and Bran

In decades past, doctors recommended bran to people with IBS under the presumption that it could improve bowel regularity. However, a landmark study published in 1994 was the first to suggest that bran tended to make IBS symptoms worse rather than better.

In its 2014 review, the American College of Gastroenterology concluded that insoluble fiber sources, like wheat bran, are not recommended for IBS due to the risk of increased gas and bloating.

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 is uniquely linked.

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, sending signals to the brain that trigger IBS symptoms.

Another possibility is that wheat bran contains a fermentable carbohydrate called fructan, 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.

Cutting back on the bran may be all that is needed to avoid IBS symptoms in some people. Over time, the amount of bran eaten can be increased as your body becomes more tolerant of the fiber.

IBS-Friendly Fiber Alternatives

If wheat bran is causing you problems, there are other fiber alternatives that you can consider. Excellent sources of insoluble fiber include:

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

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

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

Although a diet high in fiber is optimal for digestive health, some studies suggest that it may be more beneficial to people with constipation-predominant IBS (IBS-C) than the other IBS subtypes.

A Word From Verywell

There is mounting evidence that soluble fiber found in fruits, vegetables, and legumes may be better tolerated in people with IBS than insoluble fiber. If unsure which sources of fiber are best for you, meet with a dietitian experienced with IBS to work out a dietary plan. Oftentimes, it takes trial and error before the right one is found.

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

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