Digestive enzymes assist in the breakdown of food particles to make them smaller for absorption. Lactose intolerance occurs due to an absence or deficiency of the intestinal enzyme lactase. When lactose, the main carbohydrate component of milk, is not digested, diarrhea and fluid loss result. In addition, bacteria in the large intestine will metabolize the lactose to produce large quantities of gas which causes bloating and pain. It therefore seems that many of us do not have the ability to digest lactose.
Most digestion is completed in the small intestine.
While the idea of microorganisms flourishing in the body may not be that appealing, these intestinal bacteria, called the intestinal flora, have an important role in the body. Fibre, a form of dietary carbohydrate, contains cellulose. Cellulose is a structural component of plant structure and is resistant to human digestive enzymes. Cellulose can be excreted in the feces, however some of it is fermented by the bacteria present in the large intestine. Changes in the diet or in the type of microorganisms can influence the amount of gas produced.