is a sugar found in milk and milk products. The small intestine—the organ where most food digestion and nutrient absorption take place—produces an enzyme called lactase. Lactose intolerance is a common disorder and is due to the inability to digest lactose into its constituents, glucose and galactose, secondary to low levels of lactase enzyme in the brush border of the duodenum. Lactase deficiency is the most common form of disaccharides deficiency. Enzyme levels are the highest shortly after birth and decline with aging, despite continued intake of lactose. Within the animal world, nonhuman mammals usually lose the ability to digest lactose as they reach adulthood. Some populations of the human species, including those of Asian, South American, and African descent, have a propensity for developing lactase deficiency.
By contrast, races descended from northern Europe or from the northwestern Indian subcontinent are likely to retain the ability to absorb lactose into adulthood. Symptoms of lactose intolerance include loose stools, abdominal bloating and pain, flatulence, nausea, and borborygmi. A diagnosis or even the suggestion of lactose intolerance leads many people to avoid milk and/or to consume specially prepared food with digestive aids, adding to health care costs [1-3].
 Newcomer AD, McGill DB, Thomas PJ, et al. Tolerance to lactose among lactase-deficient American Indians. Gastroenterology. 1978 Jan. 74(1):44-6.
 Di Stefano M, Miceli E, Mazzocchi S, et al. Visceral hypersensitivity and intolerance symptoms in lactose malabsorption. Neurogastroenterol Motil. 2007 Nov. 19(11):887-95.
 Zhong Y, Priebe MG, Vonk RJ, et al. The role of colonic microbiota in lactose intolerance. Dig Dis Sci. 2004 Jan. 49(1):78-83.