Why Beans Cause Gas: Unveiling the Science Behind Digestive Discomfort

Beans cause gas because they contain sugars called oligosaccharides that gut bacteria ferment.

Why

Beans have oligosaccharides (raffinose and stachyose). Humans lack the enzyme to digest them, so gut bacteria ferment them and make gas.

How to reduce

• Soak beans overnight and discard the water.
• Cook thoroughly.
• Use Beano (alpha-galactosidase).
• Add beans to your diet gradually.

Benefits

Beans are high in fiber and protein.

Fact

The average person passes gas 14 to 23 times a day.

The sugar involved

Beans contain oligosaccharides such as raffinose and stachyose. Humans lack the enzyme alpha-galactosidase to break them down in the small intestine, so they pass to the colon where bacteria ferment them, producing hydrogen, carbon dioxide and sometimes methane. A cup of cooked beans provides 12 to 15 g of fiber.

• Soaking dried beans for 8 to 12 hours and discarding the water can remove some of these sugars.
• Cooking with kombu seaweed is a folk method, but evidence is limited.
• Over-the-counter alpha-galactosidase (such as Beano) can reduce gas when taken with the first bite.
• Gas production usually declines after 2 to 4 weeks of regular intake as gut bacteria adapt.

Benefits of keeping beans

Beans give protein of 15 g per cup, folate, iron and potassium. A 2012 meta-analysis in Archives of Internal Medicine found eating about a cup of legumes daily lowered LDL cholesterol by about 5 percent. Increase portions slowly and drink water. Persistent bloating with pain, diarrhea or weight loss warrants a visit to rule out conditions like irritable bowel syndrome or celiac disease.

The sugar involved

Beans contain oligosaccharides such as raffinose and stachyose, which humans cannot digest in the small intestine. Gut bacteria ferment them in the colon, producing gas. Soaking dried beans, discarding the water and cooking thoroughly can reduce these sugars. Alpha galactosidase enzyme products can help.

Benefits

Beans provide about 15 g protein and 15 g fiber per cooked cup. Gas often lessens as the gut adapts to higher fiber intake. Increase portions gradually and drink fluids.

Gut microbiology

Human intestines lack alpha-galactosidase to break down raffinose and stachyose. Bacteria like Bifidobacterium and Clostridium ferment these oligosaccharides, producing hydrogen, methane and carbon dioxide. A typical serving of beans can produce an extra 1 to 2 liters of gas.

Reducing gas

Soak dried beans 8 to 12 hours, discard water, rinse, and cook until soft. Add epazote or kombu in traditional cooking. Lentils and split peas tend to cause less gas than kidney or navy beans. A 2011 study found people’s gas decreased after 4 weeks of regular bean eating.

Based on data from the American Society for Nutrition and the Harvard T.H. Chan School of Public Health