Understanding Lactose Intolerance

What is lactose intolerance?
Lactose intolerance is the inability of the body to digest lactose, which is the major sugar found in milk. It is caused by a shortage of an enzyme called lactase, which helps the body digest the lactose found in milk and other dairy products. Roughly 50 million Americans are lactose intolerant. As many as 75% of African American, Jewish, Native American, and Mexican American adults have this condition. Up to 90% percent of Asian Americans are lactose intolerant.

What are the symptoms of lactose intolerance?
Intestinal discomfort after eating or drinking dairy foods is the main symptom of lactose intolerance. Common reactions include nausea, cramps, bloating, gas, and diarrhea. These symptoms may begin as soon as a few minutes and up to a few hours after eating dairy foods. Symptoms range from mild to severe, and may vary depending on how much and what type of dairy food is consumed.

Is lactose intolerance different than a milk allergy?
Yes. Lactose intolerance is not an allergy to milk. Although the symptoms sometimes are similar, milk allergy is an immune response that is triggered by the immune system.

What causes lactose intolerance?
Deficiency of an enzyme in the body called lactase is the cause of lactose intolerance. After about 2 years of age, the body begins to produce less lactase, resulting in problems digesting lactose. The symptoms of lactose intolerance are often not noticeable until later in life. Lactose intolerance also occurs when the small intestine is injured, such as in celiac disease or inflammatory bowel disease.

How is lactose intolerance diagnosed?
Many people identify lactose intolerance based on their symptoms. However, it is similar to other digestive problems, so it is sometimes hard to pin down. The first step in diagnosis is to remove all dairy foods from the diet to see if the symptoms go away.

Medical tests can diagnose lactose intolerance. The lactose tolerance test requires fasting before the test and then drinking a liquid that contains lactose. Blood samples are taken over a 2-hour period to measure the patient’s blood glucose level. This measures how well the body is able to digest lactose.

Another test is the hydrogen breath test. A person drinks a lactose-loaded beverage, and the breath is analyzed at regular intervals. Elevated levels of hydrogen in the breath indicate improper digestion of lactose.

I know milk is high in calcium. How can I get enough calcium without drinking milk or eating milk products?
Calcium is an important nutrient, and dairy foods are the most easily accessible source. Many people with lactose intolerance can tolerate dairy foods in small amounts. For example, you can try eating some cereal with a small amount of milk (about ¼ cup) and see if you have symptoms.

Often people with lactose intolerance can tolerate yogurt with active yogurt cultures. These cultures contain the enzyme lactase, which is required to digest the lactose found in yogurt.

Most grocery stores sell milk that is lactose free and sold under the brand name Lactaid®. Individuals with lactose intolerance often can tolerate this milk. In addition, you can purchase pills that contain lactase that you take just prior to eating dairy foods.

For individuals who prefer to avoid dairy foods, many nondairy foods provide good sources of calcium, including:

• Calcium-fortified juices
• Calcium-fortified cereals
• Calcium-fortified soy milk
• Calcium-fortified soy milk products
• Green-leafy vegetables
• Nuts
• Legumes

Do I need to avoid all foods that contain milk products?
Some people have a very low tolerance for lactose and must avoid even the smallest amount of lactose.

Foods that may contain lactose include:

• Bread
• Other baked goods
• Processed breakfast cereals
• Instant potatoes
• Soups
• Breakfast drinks
• Luncheon meats
• Salad dressings
• Candy
• Snacks
• Pancakes
• Biscuits
• Cookie mixes
• Powdered meal-replacement supplements

Other people can tolerate small amounts of lactose at one time or can tolerate some dairy foods, but not all. The level of dietary control needed depends on what each person’s body can handle.

Do medications contain lactose?
Yes, it is estimated that  lactose is used as the base for more than 20% of prescription drugs and 6% of over-the-counter medicines. Many types of birth control pills contain lactose, as do some tablets for stomach acid and gas. A pharmacist can answer questions about the amounts of lactose in various medicines, or you can read the labels to see if your medications contain lactose.

References and recommended readings
American Gastroenterological Association Patient Center. Lactose intolerance. Available at: http://www.gastro.org/patient-center/diet-medications/food-allergies-fructose-intolerance-and-lactose-intolerance#Lactose%20Intolerance. Accessed June 27, 2012.

National Digestive Diseases Information Clearinghouse (NDDIC). Lactose intolerance.
Available at: www.digestive.niddk.nih.gov/ddiseases/pubs/lactoseintolerance. Accessed June 27, 2012.

Review Date 6/12
G-1785