In the dictionary flatulence means the passing out of wind from the digestive tract> This wind passes out as a natural biological process. Every person has flatulence i.e. passes out wind. This is passed out 15 to 20 times a day and the amount of gas passed out comes to three to four pints in a day. We do not worry at all about this as this is odorless and no sound is produced.
The process of digestion involves breaking down of things. Carbohydrates break down into starches, proteins into amino acids and fats into fatty acids and glycerol. But when some of these things do not break down, gas is produced or flatulence occurs.
The undigested food enters the large intestine. If you are lactose intolerant i.e. you do not have the enzyme lactase in your intestine. This enzyme breaks lactose into two sugar molecules to be absorbed by the bloodstream. If lactase is not present lactose passes undigested food into the large intestine.
In the large intestine there are billions of hungry bacteria waiting to eat the lactose. These bacteria produce gases such as carbon dioxide, methane, hydrogen and hydrogen sulphide. Hydrogen sulphide produces the odor that is associated with flatulence.
Similarly, due to the absence of other enzymes one or the other part of the food may remain undigested and produce flatulence. This is the reason why a thing produces flatulence in some persons while it is perfectly digestible in the case of others. We say that proteins do not cause flatulence. But some times proteins can also do. So, to stop flatulence we must make survey of our diet and not when we have flatulence.