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Why Do Beans Cause Gas?

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


Updated June 16, 2014

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

Question: Why Do Beans Cause Gas?

Everyone passes gas. It's known, however, that some foods may tend to make a person produce more gas than others. In particular, foods that have a high fiber content are a frequent offender when it comes to causing gas in bloating. One food that has a particularly notorious reputation when it comes to Beans in particular are well-known for their ability to cause flatulence. Why does this happen, and can anything be done about it?


What Is Gas?

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

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

Why Do Beans Cause Gas?

Beans (legumes) cause gas because they contain a particular sugar, oligosaccharide, that the human body can not break down. Oligosaccharides are large molecules and are not broken down and absorbed by the lining of the small intestine as other sugars are. This is because the human body does not produce the enzyme that breaks down oligosaccharides.

Oligosaccharides make it all the way through the GI tract to the large intestine still intact. The bacteria that live in the small intestine break down the oligosaccharides. This produces the gas that must eventually come out of the rectum.

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 gas in the large intestine.

How To Prevent Gas

To prevent gas that is caused by eating beans, the oligosaccharides must be broken down before they reach the large intestine and become food for the resident bacteria. The enzyme that breaks down oligosaccharides is alpha-galactosidase. This enzyme is derived from the fungus Aspergillus niger and is available under the brand name Beano.

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


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