Lactose intolerance is the inability to digest significant amounts of lactose, the predominant sugar of milk. This inability results from a shortage of the enzyme lactase, which is normally produced by the cells that line the small intestine. Lactase breaks down milk sugar into simpler forms that can then be absorbed into the bloodstream.

Tolerance to lactose is variable and individual-dependent. The tolerance threshold of milk and/or dairy products can only be determined by trial and observation by qualified medical practitioners.

Milk and non-fermented dairy products, which are the natural sources of lactose, should be avoided. Fermented dairy products, on the other hand, are well tolerated because the abundant lactic acid bacteria present in these products digest the lactose.

Other food products that may contain lactose include: bread and other baked goods; processed breakfast cereals; instant potatoes, soups, and breakfast drinks; margarine; lunch meats (other than kosher); salad dressings; candies and other snacks; mixes for pancakes, biscuits, and cookies, and should be avoided.

It is important to read food labels with care, looking not only for milk and lactose among the contents but also for such words as whey, curds, milk by-products, dry milk solids, and non-fat dry milk powder. If any of these are listed on a label, the product contains lactose, and should be avoided.

In view of the fact that most of the foods listed contain important nutrients, coupled with the fact that individuals differ in the amounts and types of foods they can handle, it is important for each person to learn through trial and error how much lactose he or she can handle. Young children with lactase deficiency should not eat any foods containing lactose. Most older children and adults need not avoid lactose completely.

Additional resources:

See also the background file on lactose intolerance