Carbohydrate rich foods are often the worst offenders. Most gas results from sugars and starches. Colonies of harmless bacteria in the colon eat the carbohydrates, giving off the by-products hydrogen, carbon dioxide and methane in some people.  A special type of sugar called raffinose is found in beans and in smaller amounts in some vegetables and grains. The human body lacks the enzyme called alpha-galactosidase to digest this sugar and so bacteria in the colon have a feast.            Avoid the gas forming foods and then add back those that are tolerated well. People vary in their reactions to foods, so don't assume that what is "gassy" for someone else will be "gassy" for you.