Lactose intolerance is the most common clinical problem that limits milk and dairy products consumption worldwide and it is defined as the experience of gastrointestinal symptoms due to the intake of lactose-containing food products.1 Lactose is a disaccharide sugar that is mainly found in human and mammalian milk and vital for the nourishment of newborn infants. It is naturally metabolized into absorbable sugars, namely glucose and galactose, by the enzyme lactase in the mucosal brush-border of the intestine.2-5 It has been found that only about 35% of people worldwide are lactase persistent, who continue to produce lactase throughout adulthood, and thus are able to digest the sugar in milk without discomfort. The remaining majority of global population, owing to a deficiency of intestinal lactase enzyme, is unable to digest considerable amounts of lactose and thus presents with lactose intolerance. The unabsorbed lactose is metabolized by colonic bacteria to produce short-chain fatty acids and gas, mainly hydrogen (H2), carbon dioxide (CO2), and methane (CH4).
The gas distends the intestines and likely explains the clinical syndrome that manifests with a range of gastrointestinal symptoms including abdominal cramps, bloating, and flatulence.4,7-9 Moreover, undigested lactose creates an osmotic load that draws fluid and electrolytes into the intestinal lumen, often resulting in loose stools or osmotic diarrhea.