Lactase is required for breakdown of lactose in the small bowel into galactose and glucose, both of which can then be absorbed. Without lactase the lactose passes into the colon where it is digested by colonic bacteria, resulting in gas and other symptoms.


Lactase deficiency may occur at any age. It can present as milk intolerance in an infant. Often it first becomes apparent when the patient is an adolescent or adult. A person may slowly decrease the intake of dairy products over the years without every making the connection.


Findings in a patient with lactase deficiency following exposure to milk, cheese or other lactose source:

(1) gas with flatulence

(2) abdominal pain or cramping

(3) abdominal distention

(4) passage of loose, watery stools


Some patients are misdiagnosed as having the irritable bowel syndrome (IBS). Anyone diagnosed with IBS should be evaluated for lactose intolerance.


Reasons why a person may not be aware of the link with lactose in diet:

(1) unaware of the existence of lactose intolerance

(2) mild lactase deficiency

(3) lactose loads relatively small

(4) able to drink milk as a child

(5) belief in another explanation


The diagnosis may be made by:

(1) avoidance of symptoms by avoiding dairy products

(2) avoidance of symptoms by adding lactase (Lactaid) to food

(3) performing an oral lactose tolerance test

(4) measuring expiration of CO2 following administration of lactose radiolabelled with carbon-14


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