Piyush Rathi

Lactose intolerance is the inability to metabolize milk sugar, or lactose. Lactose is a disaccharide found in dairy products and is composed of glucose and galactose. While lactose intolerance varies wildly from population to population, scientists estimate that nearly 75% of adults either lack the ability to digest lactose or at least have difficulty digesting dairy products in general. The frequency ranges from around 5% in northern Europe to more than 90% in some Asian and African countries.

The issue of whether we can digest lactose depends upon the intestinal enzyme Lactase. Lactase (or beta-galactosidase) is the enzyme that hydrolyzes lactose into its component monosaccharides, galactose and glucose. Lactase is naturally produced in the small intestine. In the inner lumen of the small intestine, projections called villi are covered with cells known as enterocytes. These enterocytes are covered with a membrane that has what is called a brush border. The brush border is actually millions of microvilli and is the site of lactase production.

Villi are projections into the lumen of the small intestine that are covered with enterocytes. An electron micrograph of the microvilli of an enterocyte with brush border is shown

Lactase promotes the hydrolysis of the Beta-D galactoside linkage of lactose, converting it into D-glucose and D-galactose. This reaction provides two positive results for dairy products, which we will cover later in the article. Lactase is very active in the duodenum. Its ability to handle lactose loads is very closely related to the amount of lactose emptying from the stomach into the duodenum. The optimum temperature for lactase is about 48 C (118.4 F) for its activity and has an optimum pH of 6.5. 


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