Lactose Intolerance

Lactose Intolerance

What is it?

Lactose is the primary sugar found in milk and other dairy products. People who are lactose intolerant have difficulty digesting lactose, and may experience discomfort after eating dairy products.

What causes it?

Lactose is digested by an enzyme called lactase, which is produced by the lining of the small intestine. Lactase breaks lactose down into two simple sugars, glucose and galactose, which are then absorbed by your bloodstream.

People with lactose intolerance have deficient levels of lactase. As undigested lactose moves through the large intestine, it can cause discomfort. There are three types of lactose intolerance:

Primary Lactose Intolerance – Milk is the main source of nutrition for babies and infants, so the body produces more lactase during that time. As people diversify their diets, lactase production decreases, which can lead to symptoms of lactose intolerance as they age.

Secondary Lactose Intolerance – Sometimes, the small intestine decreases lactase production after an illness or injury. Intestinal diseases and inflammatory bowel diseases can cause secondary lactose intolerance, as can intestinal surgeries. This type of lactose intolerance may disappear over time, or it can be permanent.

Congenital Lactose Intolerance – This is a lifelong inability to digest lactose, and is fairly rare. It is an autosomal recessive disorder, so both the mother and father must pass the defective gene on to the child. Babies with congenital lactose intolerance require lactose-free formulas to avoid dehydration and weight loss. Some premature babies have temporary lactose intolerance, but once they begin to produce lactase, the condition goes away.

Who is at risk?

An estimated 65 to 75% of the world’s population has a decreased ability to digest lactose. Lactose intolerance has a strong genetic component. It commonly runs in families, and certain ethnicities are more prone to lactose intolerance than others. Lactose intolerance becomes more common as you age, and many people are diagnosed in their late teens and adulthood. Diseases that affect the small intestine, like Crohn’s disease and celiac disease, can also cause lactose intolerance, as can certain cancer treatments.

Lactose Intolerance by Ethnicity:

  • East Asian: 90-100%
  • Native American: 80-100%
  • Central Asian: 80%
  • African American: 75%
  • African: 70-90%
  • Ashkenazi Jew: 60-80%
  • Latino/Hispanic (North America): 51%
  • Anglo (North America): 21%
  • German: 15%
  • British: 5-15%

Signs and Symptoms

Most people with lactose intolerance are able to digest small amounts of milk and other dairy products. Symptoms of lactose intolerance generally appear between 30 minutes and 2 hours after ingestion of dairy products. Symptoms include:

  • Gas and bloating
  • Cramps and lower abdominal pain
  • Loose, foamy stools and/or diarrhea
  • Nausea and vomiting
  • Gurgling or rumbling in the lower abdomen

Ingestion of dairy products can cause temporary discomfort once in a while. If you feel ill occasionally after drinking or eating dairy, you probably do not have lactose intolerance. In people who are lactose intolerant, these symptoms appear repeatedly and frequently after ingestion of dairy.


In many cases, patients are asked to cut lactose from their diets. If the symptoms improve, this may be enough for a diagnosis. There are also blood, breath, and stool tests that can verify lactose intolerance.

Hydrogen breath test – The patient drinks a liquid that contains high amounts of lactose. When the body doesn’t digest lactose, it ferments in the colon and releases hydrogen. This hydrogen is expelled as the patient breathes, so the doctor measures the levels of hydrogen in the patient’s breath. Higher levels of hydrogen indicate that the patient may be lactose intolerant. This is the preferred method of diagnosis.

Lactose tolerance test – Lactase breaks lactose down into glucose and galactose. In this test, the patient drinks a liquid with high amounts of lactose, and blood is periodically drawn and tested for glucose levels. In patients without lactose intolerance, the levels of glucose in the blood should increase.

Stool acidity test – This test is generally used in infants and young children. Undigested lactose ferments and creates acids that can be detected in a stool sample.


There is no cure for lactose intolerance, and no way to force the body to increase lactase production. Dairy products provide critical nutrients such as calcium, and many people with low lactase levels can drink small servings of milk (about 4 ounces) without difficulty. Some dairy products are easier to digest than others. People with lactose intolerance can take calcium supplements to ensure they are getting the recommended daily amount of calcium in their diets. Alternatively, patients can add lactase enzymes to milk, or take lactase enzymes in tablet or capsule form. If dairy products are consumed along with other foods, symptoms may be reduced.

Dairy Products That May Be Easier to Digest:

  • Yogurt
  • Cottage cheese
  • Buttermilk
  • Goat’s milk
  • Lactase-treated cow’s milk
  • Soy formula for infants
  • Soy or rice milk
  • Aged or hard cheeses
  • Ice cream