Some common bacteria in the large intestine can destroy the hydrogen that other bacteria produce. The balance of the two types of bacteria may explain why some people have more gas than others. Most foods that contain carbohydrates such as sugars can cause gas. By contrast, fats and proteins cause little gas. The sugars that can cause gas are raffinose, lactose, fructose, and sorbitol.
Beans contain large amounts of the complex sugar raffinose.
Smaller amounts are found in cabbage, brussel sprouts, broccoli, asparagus, other vegetables, and whole grains. Lactose is the natural sugar in milk. It is also found in milk products, such as cheese and ice cream, and processed foods, such as bread, cereal, and salad dressing. Many people, particularly those of African, Native American, or Asian background, have low levels of the enzyme lactase needed to digest lactose. Also, as people age, their enzyme levels decrease.