Why Do Beans Cause Gas?

When It Comes To Intestinal Gas, Beans Often Top The List Of Offending Foods

Baked Beans
Beans are a healthy addition to your diet, but there's just that one little problem with how they can cause gas.. Lauri Patterson/Vetta/Getty Images

Everyone passes a certain amount of gas every day. Gas is part of the natural digestive process, and there's no getting around it. If gas isn't bothersome for any reason, it's typically not something to worry about. However, many people find gas embarrassing or even painful, and would like to have less gas. Other people think they may be passing what is an excessive amount of gas.

It is true that some foods may tend to make a person produce more gas than other foods.

In particular, foods that have a high fiber content are a frequent offender when it comes to causing symptoms of gas and bloating. It's also true, though, that most people (particularly in the United States) do not get enough fiber in their diet, and should be eating more fibrous foods. One food that has an especially notorious reputation when it comes to gas is beans. Beans are well-known for their ability to cause flatulence (there's even a little song about it that the kids like to sing).

Why do beans cause gas, and for those that love them, can anything be done to reduce the possibility of gas from eating beans?

What Is Gas?

Intestinal gas is primarily composed of hydrogen, nitrogen, and carbon dioxide—which are all gasses that are, in fact, odorless. In about one-third of people, however, intestinal gas also contains another ingredient: methane. It's unclear why some people's bodies produce methane and others do not.

One way to tell if you have methane in your gas is to look at your stool: people who produce methane typically will have stools that float in water.

Sulfur is the substance that causes gas to have its distinctive odor. Therefore, it follows that eating foods that are high in sulfur, such as garlic, onions, leeks, broccoli, cauliflower, cabbage, and Brussels sprouts, can cause a person to have foul-smelling gas.

Why Do Beans Cause Gas?

Beans (legumes) cause gas because they contain a particular sugar, called oligosaccharide, that the human body can not break down. Oligosaccharides are large molecules and are not broken down and absorbed in the same way that other sugars are: by the normal digestive process that takes place in the small intestine. This is because the human body actually does not produce the enzyme that breaks down oligosaccharides.

Oligosaccharides make it all the way through the digestive tract to the large intestine still intact and as yet undigested. It is the bacteria that live in the large intestine that finally break down the oligosaccharides. This process is the one that produces the gas that must eventually come out of the rectum as flatulence.

By the same principal, other foods that come into the large intestine without being properly absorbed in the small intestine will cause gas. For example, stress can cause food to move through the digestive tract too quickly to be properly digested, with the end result being more gas produced in the large intestine.

How To Prevent Gas

To prevent gas that is caused by eating beans or other foods, the oligosaccharides must be broken down before they reach the large intestine and become food for the resident bacteria that live there. There is an enzyme that breaks down oligosaccharides, which is called alpha-galactosidase. This enzyme (which the human body does not make) is derived from the fungus Aspergillus niger and is available for purchase under the brand name Beano and others.

Alpha-galactosidase is not appropriate for people with diabetes to take, as it may lead to an increase in blood sugar level. People who have mold allergies may have an allergic reaction to alpha-galactosidase, so it may not be an option in these cases. Alpha-galactosidase may increase galactose levels and therefore should not be used by those who have the genetic disease galactosemia.

Source:
Di Stefano M, Miceli E, Gotti S, Missanelli A, Mazzocchi S, Corazza GR. "The effect of oral alpha-galactosidase on intestinal gas production and gas-related symptoms." Dig Dis Sci. 2007 Jan;52:78-83.

Winham DM, Hutchins AM. "Perceptions of flatulence from bean consumption among adults in 3 feeding studies." Nutr J. 2011 Nov 21;10:128.

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