Understanding lactose intolerance


By pH health care professionals

Lactose intolerance comes from a deficiency in an enzyme needed for digesting lactose, called lactase. Lactase is an intestinal enzyme that breaks down lactose to glucose and galactose, which are simple sugars. Lactase concentration is high at birth but declines steadily in most people of non-European ancestry after weaning. This normal decline occurs to a greater extent in some people than in others.

Approximately 50 million people in the US have partial to complete lactose intolerance.  As many as 90 percent of Asian-Americans, 70 percent of African-Americans, 95 percent of Native-Americans, 50 percent of Mexican-Americans and 60 percent of Jewish-Americans are lactose intolerant, compared to only less than 25 percent of white adults.  


Symptoms of lactose intolerance vary depending upon the severity of lactase deficiency and the amount of lactose ingested. 

Most people with lactose intolerance can drink one or two glasses of milk daily without symptoms, if taken with food at wide intervals. Some have complete intolerance. Symptoms include bloating, abdominal cramps and flatulence. Sometimes diarrhea may occur. Symptoms, however, do not result in weight loss or other signs of malabsorption.

Because symptoms can be nonspecific, it can mimic a number of gastrointestinal disorders such as inflammatory bowel disease, irritable bowel syndrome and pancreatic insufficiency.  Lactase deficiency may also occur with these disorders; thus it always needs to be considered.


The most widely used test is the hydrogen breath test done in a doctor’s office. Fifty grams of lactose is ingested and within 90 minutes, a rise in breath hydrogen is a positive test.  Your doctor may have you restrict lactose from the diet for two weeks.  Resolution of symptoms is suggestive of deficiency and may then be confirmed.


Lactase deficiency symptoms are uncomfortable. The goal of treatment is patient comfort. Often, people know the amount of lactose they can tolerate. Foods that are high in lactose include milk (12 g/cup), ice cream (9 g/cup) and cottage cheese (8 g/cup).  Aged cheeses have lower lactose content (0.5 g/oz). Spreading dairy product intake throughout the day in quantities of less than 12 g per serving usually does not cause symptoms.

Some people require lactase supplements to improve lactose absorption. There are also dairy products that have been pre-treated with lactase, and thus are lactose-free.

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