Flatulence
Undigested lactose reaches the large intestine where it encounters the gut microflora comprising a number of bacteria that does ferment lactose but unlike the preceding parts of the gastrointestinal tract, there is no absorption system for carbs in the large intestine. As long as the lactose stays in the colon there is abdominal discomfort. Fermented by the gut bacteria, lactose is broken down to produce hydrogen, carbon dioxide and methane gas and a few fatty acids. Fatty acids are used by the bacteria to meet their energy requirements. The gas however accumulates and finally occupies colon and cause flatulence. The microflora’s efficiency to ferment lactose varies individually and hence extent of flatulence may vary person to person.