Legumes and flatulence

Many legumes contain large amounts of indigestible carbohydrates, such as oligosaccharides and cell-wall cements. The human body cannot break down these carbohydrates; therefore, they pass through the stomach in their complex form. Resident, symbiotic bacteria in the intestine break them down into absorbable forms. The increased growth and metabolism of the intestinal bacteria cause a sudden increase in gas production. 

Cooks can help minimize flatulence by manipulating legumes before consumption. Prolonged cooking helps break down much of the oligosaccharides and cell-wall cements into digestible single sugars. Oligosaccharides are also broken down during germination and fermentation, so sprouts, miso, soy sauce, and extracts like bean curd are less offensive than whole beans.