|MadSci Network: Anatomy|
Beans (and many other seeds) contain specific types of oligosaccharides (polymers of 3 to 5 glucose molecules) that are not digested by the enzymes in the small intestine. This means they pass into the large intestine, where they are, at least partially, digested by the bacteria in the large intestine. Carbon dioxide and hydrogen gas are produced by these bacteria and pass through the rectum. There are many factors that determine the extent to which beans may lead to gas production--type of gut bacteria, general activity of the gut, amount of air swallowed with the food, and type of bean. In general, dried lima beans and navy beans lead to more gas formation than other types of dried beans, while immature beans lead to less gas formation. These oligosaccharides are water-soluble and the amount of them in the final food can be redcued by soaking the beans and then discarding the soaking water or by bringing the beans to a boil, boiling for a couple of minutes and then discarding that cooking water.
Source: McGee, Harold. On Food and Cooking. 1984,
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