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Are you Lactose Intolerant?

Lactose is the sugar found in milk and dairy products such as cheese and yogurt. After eating dairy products that contain this sugar, usually lactase, a digestive enzyme of the small intestine, helps to breakdown this complex sugar into two simple sugars, glucose and galactose. These simple sugars are then absorbed in the small intestine and ultimately reach the blood stream where they act as nutrients. The enzyme lactase is located in the lining of the small intestine known as the intestinal villi.

In addition to milk and dairy products such as ice cream, yogurt and cheese, lactose can be found in bread and baked goods, processed breakfast cereals, instant potatoes, some soups and non-kosher lunch meats, candies, dressings and mixes for pancakes and biscuits. Lactose is also the sugar found in breast milk and standard infant formulas. Therefore almost all babies are able to digest and absorb this sugar and it serves as their primary dietary sugar.


Because lactose is not digested properly in the small intestine of individuals who are lactose intolerant, it passes whole into the large intestine or colon. Upon reaching the colon it is broken down by the normal colon bacteria. This breakdown results in the production of carbon dioxide and hydrogen gases. The gas production can lead to the following common symptoms:

  • • Abdominal distension and pain
  • • Excess burping
  • • Loud bowel sounds
  • • Excess gas and diarrhea following ingestion of lactose.
  • • Watery and explosive bowel movements
    • Urgency with bowel movements, which means that children feel that they have to get to the bathroom immediately or they will have an accident.

The symptoms of lactose intolerance can start during childhood or adolescence and tend to get worse with age. The severity of symptoms is usually proportional to the amount of the milk sugar ingested with more symptoms following a meal with higher milk sugar content.

Although eating lactose-containing products will result in discomfort for someone who is lactose intolerant, they are not at risk of developing more serious intestinal disease because of long-term lactose malabsorption. The only exception to this would be for babies who are born with primary lactase deficiency or children with secondary lactase deficiency as discussed below.


Primary Lactase Deficiency:
 This condition is very rare and occurs when babies are born with a deficiency or absence of the enzyme lactase. Babies inherit this condition by getting one gene that causes this problem from each of their parents, even though both parents may be lactose tolerant. These babies require a specialized formula with another type of sugar such as sucrose (present in table sugar), which they are able to digest.

Secondary Lactase Deficiency: The most common cause of temporary lactose intolerance in infants and young children is infection that affects the gastrointestinal tract and can damage the lining of the small intestine.

Rotavirus and Giardia are two common organisms that cause damage to the surface of the small intestine resulting in temporary lactose intolerance. Older infants and young children will commonly be infected by a rotavirus. The symptoms of rotavirus infection symptoms include vomiting, diarrhea (frequent, watery stools), and fever. Giardia is a parasite that is found in well water and fresh water from lakes and streams. Treatment of giardia infection with antibiotics will resolve the lactose intolerance.

Secondary lactase deficiency can also be due to Celiac disease, which is intolerance to gluten, the protein found in wheat, rye, barley and other grains. Crohn’s disease, an inflammatory condition that can affect any part of the gastrointestinal tract, can lead to secondary lactase deficiency as well. Once each of these conditions is treated, the lactase deficiency will resolve. The lactose intolerance usually resolves within three to four weeks when the lining of the intestines returns to normal.

Acquired Lactase Deficiency: Many individuals acquire lactose intolerance as they get older. It is estimated that approximately one-half of adults in the United States have acquired lactase deficiency. This condition is due to a normal decline in the amount of the enzyme lactase present in the small intestine as we age. Although lactose is an important part of the diet in infants and young children it represents only 10% of the carbohydrate (sugar) intake in adults. However, individuals who are lactose intolerant may not be able to tolerate even small amounts of this sugar in their diet.

Lactose intolerance occurs more frequently in certain families. One of the most important factors affecting the rate of developing lactose intolerance is an individual’s ethnic background. Approximately 15% of adult Caucasians, and 85% of adult African Americans in the United States are lactose intolerant. The rate of lactose intolerance is also very high in individuals of Asian descent, Hispanic descent, Native Americans and Jewish individuals.


Lactose intolerance is diagnosed by a simple test called a hydrogen breath test. After an overnight fast before the test, an individual breathes into a bag and then drinks a specified amount of the milk sugar in the form of a syrup. In adults this corresponds to the amount of milk sugar in a quart of milk. Subsequent breath samples are taken for up to three hours. The breath that they exhale into the bag is analyzed to determine its hydrogen content. During the course of the test individuals who are lactose intolerant will have an increase in the amount of hydrogen that they exhale. If the values for hydrogen increase above a certain value, the diagnosis of lactose intolerance is made. Patients who are lactose intolerant may also develop their typical symptoms during the test.

In younger children or in children who cannot tolerate the breath test, removal of lactose from the diet and possible supplementation with lactase can be done for 2-4 weeks to see if this improves the symptoms.

The best treatment of lactose intolerance is a combination of dietary modification and taking a supplement to aid in digestion of lactose. Individuals who are lactose intolerant should meet with a dietician to review the sources of lactose in their diet. Some reduction in the daily lactose consumption is usually required. When an individual is going to be eating a food that contains lactose they should take a commercially available non-prescription lactase supplement at the time of lactose ingestion. This type of supplement can be taken throughout the day whenever lactose is ingested. Some individuals will be less lactose intolerant and therefore will be able to tolerate comparatively larger amounts of lactose. Alternatives to milk for lactose intolerant individuals include products such as soy milk. If an individual is restricting their milk/ dairy intake it is important to ensure adequate supplementation of calcium and Vitamin D in the diet. This is especially important for pediatric patients and women.

Recommended daily calcium intakes:
1-3 years of age: 500 mg
4-8 years of age: 800 mg
9-24 years of age: 1300 mg
Age 25 and above: 800-1000 mg
Pregnant and nursing women: 1200 mg


Author(s) and Publication Date(s)

Marsha H. Kay, MD, The Cleveland Clinic, Cleveland, OH, and Anthony F. Porto, MD, MPH, Yale University/Greenwich Hospital, Greenwich, CT – Updated December 2012.

Marsha H. Kay, MD, The Cleveland Clinic, Cleveland, OH, and Vasundhara Tolia, MD, Children’s Hospital of Michigan, Detroit, MI – Published September 2004.