lactose intolerance

Lactose intolerance is the inability to digest significant amounts of lactose (milk sugar). It is caused by a lack or deficiency of lactase, an enzyme produced in the small intestine that separates lactose into glucose and galactose. When a person with lactose intolerance consumes milk or other dairy products, some or all of the lactose they contain remains undigested, retains fluid, and ferments in the colon. This fermentation causes abdominal cramps, bloating, diarrhea, and excess gas.

Lactose intolerance can cause discomfort and digestive upset, but it is not a serious threat to health and it can be managed through diet.

Signs of Lactose Intolerance in Adults

Most symptoms of intolerance begin 30 minutes to 2 hours after eating or drinking foods containing lactose. The severity of the symptoms depend on the amount of lactose the individual can tolerate.

Common symptoms include:

  • nausea
  • cramps
  • bloating
  • gas
  • diarrhea

Signs of Lactose Intolerance in Children

In infants, lactose intolerance can occur after a severe bout of gastroenteritis, which damages the lining of the intestine. Signs in infants can include foamy diarrhea with diaper rash, slow weight gain, slow weight development, and vomiting.

Excess Gas?

People with lactose intolerance do not produce enough of the lactase enzyme to break down lactose. When this happens, undigested lactose sits in the stomach, causing gas, bloating, and stomach cramps. When the intestine cannot absorb the lactose-containing foods, diarrhea occurs.

What causes Lactose Intolerance?

Some of the most common causes are:

  • problems with the digestive tract
    • People with irritable bowel syndrome, regional enteritis, ulcerative colitis or Crohn’s disease have a reduced level of the lactase enzyme. People with diseases of the gastrointestinal tract, such as celiac disease, may also have lactose intolerance
  • medications
    • Certain antibiotics can trigger temporary intolerance by interfering with the intestine’s ability to produce the lactase enzyme
  • infection
    • After a bout of infectious diarrhea, some kids can develop a temporary intolerance that usually improves after a few days or weeks
  • age
    • As people get older, their bodies usually stop producing the lactase enzyme, and most people will naturally become lactose intolerant over time

Lactose Intolerance and Milk Allergy

Lactose intolerance is different from milk allergies. It specifically refers to a syndrome caused by the failure to digest milk sugar. A person with a milk allergy may be able to digest milk normally, but their immune system then has an allergic reaction to one or more of the milk’s components.


Lactose intolerance is fairly common. Between 30 and 50 million Americans are lactose intolerant. Certain ethnic and racial populations are more widely affected than others. As many as 75 percent of all African Americans and American Indians and 90 percent of Asian Americans are lactose intolerant. Lactose intolerance is least common among persons of northern European descent.

How is it Diagnosed?

The most common tests used to measure the absorption of lactose in the digestive system are the lactose tolerance test, the hydrogen breath test, and the stool acidity test. These tests are performed on an outpatient basis at a hospital, clinic, or doctor’s office.

How is it Treated?

Fortunately, lactose intolerance is relatively easy to treat. No treatment can improve the body’s ability to produce lactase, but symptoms can be controlled by avoiding milk and all dairy products except yogurt. This is the most important change in diet for anyone who is intolerant of lactose. Soy milk and soy cheese are suitable replacements for cow’s milk and cheese.