Why Bran Is Bad for IBS

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If you have irritable bowel syndrome (IBS), it's important to include fiber in your diet. However, not all sources of fiber are the same, and some are not recommended if you have IBS. Bran fiber, especially, can lead to stomach upset and constipation and make IBS symptoms worse.

This article will explain how bran fiber is different from other kinds of fiber and why it can worsen symptoms of IBS. You will also learn about types of fiber that are IBS-friendly.

Bowls of oat bran and oat bran flakes
Westend61 / Getty Images

What Is Bran?

Bran is a form of fiber that is extracted from the hard outer layer of cereal grains like barley, corn, oats, rice, and wheat.

Bran can be found in bran cereals, muffins, and products made with whole wheat flour. Whole wheat flour is made of the wheat germ (the inner part of the grain kernel), endosperm (the bulk of the grain kernel), and bran. These are all milled together in the flour.

The bran content aids in digestion and provides more nutritional components than refined (white) flour. Wheat bran is also an excellent 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.

IBS and Bran

There is no definite answer as to why bran can make symptoms worse for people with IBS. Researchers have some theories, however.

One theory is that the hard bran shell is irritating to nerves in the lining of the intestines. These nerves are part of the enteric nervous system (ENT) in the gut. The ENT is responsible for regulating the digestive process. The dysfunction of the ENT is a major factor in IBS. Bran may make it even harder for the ENT to function properly.

Another possibility is that wheat bran contains fructan, one of several substances classified as a FODMAP (fermentable oligosaccharides, disaccharidesmonosaccharides, and polyols).
These are short-chain carbohydrates found in many different foods. FODMAPs can ferment and increase the amount of liquid and gas in the intestines. 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. Wheat bran is an insoluble fiber. This means that it 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 (gas).

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 your intake of bran may be all that is needed to control your IBS symptoms. Over time, it may be possible to slowly increase the amount of bran you eat as your body becomes more use to this fiber.

IBS-Friendly Fiber Alternatives

While insoluble fiber can make IBS worse, soluble fiber can be beneficial for people with IBS. In their recent guidelines, the American College of Gastroenterology concluded that soluble fiber may not only help reduce IBS symptoms but can also help lower cholesterol and blood sugar.

If wheat bran is causing you problems, here are some sources of soluble fiber that may be less irritating:

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

You may also be able to tolerate non-wheat sources of bran (such as corn, oats, and rice), particularly if constipation is an issue.

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

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

Summary

Fiber is an important part of your diet if you have IBS. However, wheat bran—extracted from the hard outer shell of the grain—is known to make IBS symptoms worse. It's not completely clear why this is, but one theory is that the hard shell irritates the intestines. Other forms of fiber, such as those in some fruits and vegetables, tend to be easier on the digestive system in people with IBS.

A Word From Verywell

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. Often, finding the best fit takes trial and error.

It's always best to use a gradual approach when increasing your fiber intake, or when trying new foods, to allow your body time to adjust to the change.

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  3. El-Salhy M, Ystad SO, Mazzawi T, Gundersen D. Dietary fiber in irritable bowel syndrome (Review). Int J Mol Med. 2017;40(3):607-13. doi:10.3892/ijmm.2017.3072

  4. Cozma-Petruţ A, Loghin F, Miere D, Dumitraşcu DL. Diet in irritable bowel syndrome: What to recommend, not what to forbid to patients. World J Gastroenterol. 2017;23(21):3771. doi:10.3748/wjg.v23.i21.3771

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  6. Cockerell KM, Watkins AS, Reeves LB, Goddard L, Lomer MC. Effects of linseeds on the symptoms of irritable bowel syndrome: a pilot randomised controlled trial. J Hum Nutr Diet. 2012;25(5):435-43. doi:10.1111/j.1365-277X.2012.01263.x

Additional Reading

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.