Lactose is a natural sugar found in milk. A person is said to be lactose intolerant when his/her body is unable to break down lactose into simple sugars during digestion. This is due to the absence of an enzyme called lactase found in the small intestine, and can lead to a myriad of symptoms, including bloating, diarrhea and stomach pain, because lactose moves into the large intestine without being broken down or absorbed in the form of its breakdown products, glucose and galactose.

Primary lactase deficiency is the most common cause of lactose intolerance, and is an inherited condition. It usually develops between the ages of 2 and 20 years.

Secondary lactase deficiency is a shortage of lactase that is caused by a problem in the small intestine. It can occur at any age, and may be the result of another condition, surgery to the small intestine or it can be caused by some medications.

A very small number of people may be born with inherent lactose intolerance, called congenital lactase deficiency.


Foods that contain lactose include:

All animal dairy products, such as milk, cheese and yogurt

biscuits and chocolate (may contain added lactose)

breakfast cereals and other breakfast items

Lactose plays an important role in the body in the absorption of calcium and magnesium.



The signs and symptoms of lactose intolerance usually begin 30 minutes to two hours after eating or drinking foods that contain lactose. Common signs and symptoms include:

  • Diarrhea
  • Nausea, and sometimes, vomiting
  • Abdominal cramps
  • Bloating
  • Gas


One or more of the following tests may be performed to confirm lactose intolerance in a patient whose history may be suggestive of the disease:

  • Lactose tolerance test. The lactose tolerance test gauges your body’s reaction to a liquid that contains high levels of lactose. Two hours after drinking the liquid, you’ll undergo blood tests to measure the amount of glucose in your bloodstream. If your glucose level doesn’t rise, it means your body isn’t properly digesting and absorbing the lactose-filled drink.
  • Hydrogen breath test. This test also requires you to drink a liquid that contains high levels of lactose. Then the amount of hydrogen in your breath is measured at regular intervals. If your body doesn’t digest the lactose, it will ferment in the colon, releasing hydrogen and other gases, which are absorbed by your intestines and eventually exhaled. Larger than normal amounts of exhaled hydrogen measured during a breath test indicate that you aren’t fully digesting and absorbing lactose.
  • Stool acidity test. For infants and children who can’t undergo other tests, a stool acidity test may be used. The fermenting of undigested lactose creates lactic acid and other acids that can be detected in a stool sample.


Treatment for lactose intolerance depends on how sensitive you are to foods that contain lactose. The condition can usually be controlled by monitoring your diet.

If you decide to experiment with what you can and cannot eat, make sure that you introduce new foods gradually rather than all at once. This will help you to get used to any foods that you might be sensitive to.

Missing out on the nutrients provided by products that contain lactose can lead to deficiencies in calcium, plus other important minerals. It is particularly important for young children to have certain nutrients in their diet to ensure healthy growth and development.

Some dairy products may be easier to digest than others. Cheese, for example, usually contains less lactose than milk. In particular, fermented dairy products, such as yoghurts, are often easier to digest.

Fermented dairy products are products that have been broken down by substances, such as yeast, bacteria, or other micro-organisms. This means that the lactose they contain will already be partially broken down, and they may be easier to digest than fresh dairy products.

Possible dairy products you could try include:

  • yoghurts, including probiotic yoghurts (that contain live bacteria)
  • probiotic milk
  • sour cream
  • cottage cheese
  • hard cheeses, such as Edam and Cheddar

It is important that you do not eliminate dairy products completely from your diet because they provide essential nutrients.


If you are unable to eat most dairy products, you may not be getting enough calcium in your daily diet. You can stock up on calcium by eating foods such as:

  • broccoli
  • cabbage
  • okra (a green vegetable, shaped like a pod that is about 5-18cm (2-7 inches) long
  • kale (a leafy green vegetable)
  • dried fruit
  • soya drinks with added calcium
  • soya beans
  • tofu (a food product that is made from soya beans and is often used by vegetarians as a substitute for meat)
  • nuts (such as almonds, brazil nuts and sesame seeds)
  • fish containing edible bones (for example, sardines, salmon, and pilchards)

Dr. Annie

Physician, mom and wife

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