Why do beans cause gas?

Beans are a great health food and are relatively inexpensive. They provide a source of plant based protein, are low in fat, high in fiber, and rich in vitamins and minerals. In multiple studies, when beans were eaten several times per week, there were significant drops in total cholesterol levels and LDL cholesterol levels.

They provide a source of soluble fiber which is beneficial for many reasons: it attaches to cholesterol particles in the digestive tract (which is supported by the studies showing drops in cholesterol), it helps increase feelings of satiety which can assist in weight loss, and it helps keep bowel movements regular. The high fiber content and type of sugar in beans also make it a low GI food which means it does not cause large spike in blood sugar. All of those benefits do have a slight downside that many of us know well: flatulence.

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So why do beans cause gas?

The answer is this: sugar molecules, called oligosaccharides, which are polymers of smaller sugar molecules. The three kinds contained in beans are: stachyose, raffinose, and verbascose. These oligosaccharides cannot be broken down by our stomach or small intestines because we do not have enzyme for them (called alpha-galactosidase), and so they reach the large intestine intact where they are broken down by bacteria. During the process of breaking down these large sugars, bacteria produce gasses such as carbon dioxide, hydrogen, sulfur, and in some people, methane. It is this process of fermentation that creates gas and intestinal discomfort.

In a study published in “Nutrition Journal”, the relationships between different kinds of beans and levels of stomach discomfort and flatulence were analyzed. In the test groups who ate pinto beans or baked beans, less than half reported increases in gas. An even lower percentage of people in the black-eyed peas group (less than a quarter) reported increased gas. It was also found that the control group who did not consume beans, also reported small increases in gas.

The benefits of eating beans seem to far outweigh the gas that is caused by their digestion, but here are some ways to decrease discomfort. Soak beans overnight before you cook them and cook them in different water than they were soaked in; start by eating small amounts at a time so your body can adjust; or take a gas easing medication. There are many medications that contain alpha-galactosidase to help your body break down those oligosaccharides, and they help greatly ease digestion.


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