Lactose intolerance overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Lactose intolerance (or hypolactasia) is the term used to describe a decline in the level of lactase, an enzyme needed for proper metabolization of lactose (a sugar that is a constituent of milk and other dairy products), in human beings. Although an estimated 70% of adult humans are considered lactose intolerant, it is uncommon in healthy northern westerners and a few others groups.

There are three major types of lactose intolerance:

1. Primary lactose intolerance. Environmentally induced by weaning in non dairy consuming societies. In most Asian and African cultures, mother's milk is the only commonly available milk and so milk consumption beyond infancy is not commonplace, therefore children become weaned, which is the same weaning process for all mammals (domesticated and wild). However societies such as the japanese where milk consumption has been on the increase, demonstrate that notwithstanding the genetic predisposition to lactose intolerance, they now present lower prevalence of lactose intolerance. For any given individual the degree of weaning is probably genetically influenced.
2. Secondary lactose intolerance. Environmentally induced, resulting from certain gastrointestinal diseases, including exposure to intestinal parasites such as giardia. In such cases the production of lactase may be permanently disrupted.[2] + (Wiser 2000, Pennardt 2006).
3. Congenital lactase deficiency present at birth and diagnosed in early infancy.

Without lactase, the lactose disaccharide in many dairy products remains uncleaved and can not be absorbed through the intestinal wall into the bloodstream, so remains in the intestines. Enteral bacteria adapt to the relative abundance of this undigested sugar and their operons quickly switch over to lactose metabolism, which produces copious amounts of gas by fermentation.

This also causes a range of unpleasant abdominal symptoms, including stomach cramps, bloating, flatulence and diarrhea. As with other unabsorbed sugars (mannitol), the lactose raises the osmotic pressure of the colon contents, preventing the colon from reabsorbing water and hence causing a laxative effect to add to the excessive gas production.