According to the National Digestive Diseases Information Clearinghouse, gas in the digestive tract causes someone to be gassy. That gas generally results after air is swallowed and by the bacterial breakdown of some foods in the large intestine. People's stomachs and small intestines do not completely digest some carbohydrates, which then go on to the large intestines. The bacteria there release and create gas in the process.
Mayo Clinic explains that high-fiber foods, fiber supplements and carbonated beverages as well as eating and drinking too quickly can cause someone to be gassy. Inflammatory bowel disease or other health issues can also cause someone to be gassy. Intolerance of dairy and certain food additives can also lead to gas because of difficulty in breaking down the sugar in these foods.
The National Digestive Diseases Information Clearinghouse points to some specific foods, such as cabbage, Brussels sprouts, onions, pears, apples and whole wheat grains, as causing gas. Gum and candy with sugar alcohols, such as xylitol, sorbitol and mannitol, can also cause someone to be gassy. It is normal for people to pass gas from 13 to 21 times a day; having abnormal amounts of gas is rare. Burping, passing gas, bloating and abdominal discomfort are some signs of gassiness.