Lactose Intolerance

Lactose intolerance is a condition in which the body cannot digest lactose properly. Lactose is primarily a milk sugar that can be found in many dairy products. Enzymes break down lactose in the intestinal tract, but when these enzymes cannot perform this function properly, the result is cramping, gas, bloating, and diarrhea. The enzyme involved in this breakdown process is called lactase. This condition is also less commonly known as lactase deficiency.1

Who Can Develop Lactose Intolerance?

Small children and infants have a large amount of the enzyme lactase to digest their mother's milk. In some people, the lactase is reduced over time and sometimes disappears. Some ethnic groups such as African-Americans, Jews, Native Americans, and 90% of Asians are more prone to develop lactose intolerance.

Symptoms of Lactose Intolerance

Symptoms of lactose intolerance begin to occur when unbroken lactose reaches the large intestine. The lactose is broken down by intestinal bacteria into lactic acid and other chemicals.2

Primary symptoms include:
  • abdominal cramps
  • bloating
  • gas
  • diarrhea
  • nausea
  • gut rumbling

These symptoms typically occur between 30 minutes and two hours after eating foods containing lactose.

Types of Lactose Intolerance

There are three types of lactose intolerance3:

Primary lactose intolerance

In primary lactose tolerance, the amount of lactase enzyme decreases over time and appears to drop sharply by adulthood. This is the most common type and starts from childhood.

Secondary lactose intolerance

Secondary lactose intolerance occurs after an illness, injury, or surgery involving the small intestine. Celiac disease and Crohn’s disease can also be a reason for this type of intolerance.

Congenital lactose intolerance

Congenital lactose intolerance is a rare form of lactose intolerance in which babies are born with lactose intolerance due to the absence of the lactase enzyme.


These tests are necessary to either rule out or confirm lactose intolerance.

Lactose tolerance test

After several hours, a measured dose of lactose is ingested and blood sugar is determined. If the blood sugar level rises, then lactase will be present; otherwise, it will not.

Hydrogen breath test

When the colon's bacteria breaks down lactose, due to a lack of the lactase enzyme, hydrogen gas is released from the lungs. Therefore, an increased amount of hydrogen in the breath after ingesting a lactose diet indicates lactose intolerance.

Stool acidity test

When lactose is broken down in the large intestine, it is converted into lactic acid. The stool acidity test can detect increases in stool acidity, indicating lactose intolerance.

The stool acidity test is mostly done for infants or small children who cannot perform the other tests.


Treatment of lactose intolerance varies from person to person. People with milder symptoms must cut out a large amount of lactose from their diet to see symptoms lessen. Those with more severe symptoms are advised to keep a strict lactose-free diet. Foods that contain milk should be avoided, such as:

  • whey or whey protein concentrate
  • casein
  • curds
  • cheese
  • butter
  • yogurt
  • margarine
  • dry milk solids or powder

Calcium Supplements

Avoiding milk and products that contain milk may cause you to become calcium deficient. Calcium is necessary for strong bones and good health, so calcium supplements are often necessary to fulfil these requirements.

Other Options

  • lactose-free milk substitutes such as rice milk, almond, soy
  • lactase drops
  • lactase tablets


  1. Malik TF, Panuganti KK. Lactose Intolerance. StatPearls. Published online May 2, 2022. Accessed July 1, 2022.
  2. Sahi T. Genetics and epidemiology of adult-type hypolactasia with emphasis on the situation in Europe. Scand J Nutr. 2001;45(4):161-162. doi:10.3402/FNR.V45I0.1799
  3. Deng Y, Misselwitz B, Dai N, Fox M. Lactose Intolerance in Adults: Biological Mechanism and Dietary Management. Nutrients. 2015;7(9):8020. doi:10.3390/NU7095380

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