Why Do Beans Cause Gas?

Bowl of pinto beans, lentils, kidney beans, navy beans, and lima beans

Verywell / Zorica Lakonic

You may have wondered why beans cause gas—and the answer may surprise you.

It's true that certain foods cause some people to produce more gas than others. In particular, foods with a high fiber content are more likely to cause gas—and bloating, too.

This article explains why beans cause gas and what you can do about it.

Understanding Gas

Most people pass gas between 13 and 21 times a day (though it's not exactly something you would keep track of). It can happen even while you're asleep. Gas is part of the natural digestive process.

Intestinal gas consists of hydrogen, nitrogen, and carbon dioxide. These gasses are odorless. Another element exists in the intestinal gas of about one-third of people: methane. Bacteria in the large intestine release gases that contain sulfur which produces the unpleasant smell of gas.

It's unclear why some people's bodies produce methane and others do not. One way to tell if there is methane in gas is to look at the stool. People who produce methane typically have stools that float in water.

Sulfur is the substance that gives gas its distinctive odor. It follows, then, that eating foods high in sulfur—such as garlic, onions, broccoli, cauliflower, and cabbage—can cause your gas to be stinkier.

Why Beans Cause Gas

Beans (legumes) cause gas because they contain a particular type of sugar, called oligosaccharide, that the human body cannot fully digest. Other sugars are broken down and absorbed in the small intestine, but the human body does not produce an enzyme that breaks down oligosaccharides.

Oligosaccharides in beans make it all the way to the large intestine undigested. Bacteria in the large intestine finally feed on these sugars.

Doing so causes fermentation (a chemical breakdown) and the production of gas. We release that gas as flatulence.

In some ways, the gas produced by eating beans is actually good for you. Gas is a byproduct of the fermentation that takes place in the gut as beans are being digested. The fiber and sugars in beans serve as food (sometimes called prebiotics) for "good" bacteria in the digestive system.

Other foods that enter the large intestine without being absorbed in the small intestine can cause gas, too. Stress can also affect digestion and nutrient absorption. The result? More gas.

When to Call Your Doctor

Gas may be a natural function, but you should talk to your doctor if your symptoms:

Preventing Gas From Beans

Most people do not get enough fiber in their diet and should eat more fibrous foods, so eliminating beans from your diet is not the preferred solution.

To prevent gas that is caused by eating beans or other foods, the oligosaccharides must be broken down before they reach the large intestine.

An enzyme called alpha-galactosidase can do this. But you will need help since the human body does not produce this enzyme. Here are a few ways to reduce the gas-producing effect of beans:

Soak dried beans: Soaking beans before cooking (and changing the water several times) has been found to reduce the amount of raffinose and stachyose—two oligosaccharides (sugars) that cause flatulence. You can do this in two ways: Soak beans overnight or boil them for two or three minutes and then allow them to soak for an hour.

Rinse canned beans: The liquid contains starch released from the beans, so rinsing them may reduce the oligosaccharide content.

Increase portions gradually: Start with a few tablespoons of beans and gradually increase the portion as your digestive tract adjusts. You may notice an increase in gas at first when you add more beans to your diet, but your stomach will adjust and you'll produce less gas as you eat them regularly.

Take a supplement: Take the enzyme alpha-galactosidase as a supplement right before a meal. Derived from the fungus Aspergillus niger, it is available in pill form under the brand name Beano and others.

Alpha-galactosidase may not be appropriate for people with diabetes. The increased breakdown of oligosaccharides can raise blood sugar.

Alpha-galactosidase may also increase levels of a sugar called galactose in the blood. People with the genetic disease galactosemia should not use it. People with this disorder can't process galactose, so the sugar builds up in the body to toxic levels and can lead to a wide range of complications.

Summary

Beans cause gas because they contain a type of sugar, called oligosaccharide, that the body cannot break down. Gas can cause pain and discomfort, but beans are good for your digestive tract, so trying strategies to reduce or prevent gas may be the best solution.

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.
  1. National Institute of Diabetes and Digestive and Kidney Diseases. Symptoms and causes of gas in the digestive tract.

  2. Johns Hopkins Medicine. Gas in the digestive tract.

  3. American Psychological Association. Stress effects on the body: Gastrointestinal system.

  4. The Bean Institute. Two ways to soak beans to reduce gas.

  5. The Bean Institute. Beans, beans, the magical "fruit": the more you eat, the less you toot!

  6. National Institute of Diabetes and Digestive and Kidney Diseases. Treatment for gas in the digestive tract.

By Amber J. Tresca
Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16.