Do you experience bloating after drinking milk? If so, you may have lactose intolerance

By John Leung MD, Christianna Moran and Rebecca Stanski


What is lactose intolerance?

Lactose intolerance is a very common condition in which people experience abdominal symptoms shortly after consuming milk or milk products.


A hydrogen breath test is being conducted by Dr. John Leung to evaluate for lactose intolerance. (Image courtesy of John Leung.) 梁爾尊醫師(右)幫一位病人做氫氣呼吸測試,該測試評估鑑定乳糖不耐症。(圖片由梁爾尊醫師提供。)

A hydrogen breath test is being conducted by Dr. John Leung to evaluate for lactose intolerance. (Image courtesy of John Leung.)

What is lactose?

Lactose is a sugar that is found in milk and milk products. It is broken down by an enzyme called lactase (produced in the small bowel) into smaller sugars that can be absorbed by the body.


What are the symptoms?


  1. abdominal bloating, a feeling of fullness or swelling in the abdomen
  2. abdominal pain
  3. diarrhea
  4. gas


How common is lactose intolerance?

90% Asians
70% African & African Americans
50% Hispanics
20% Caucasians


How is lactose intolerance diagnosed?

In addition to a history and physical, a doctor may order a simple hydrogen breath test to confirm the diagnosis. This test measures the amount of hydrogen in a person’s breath before and after eating lactose. Normally, only a small amount of hydrogen is found in the breath when a person eats lactose. However, in a person with lactose intolerance, undigested lactose produces high levels of hydrogen in the breath.


I have been diagnosed with lactose intolerance, should I avoid lactose completely?

No! Most people with lactose intolerance can tolerate some amount of milk and do not need to avoid milk and milk products completely. Research suggests that adults and adolescents with lactose intolerance could eat or drink at least 1 cup of milk a day without symptoms or with only minor symptoms.


Why not simply avoid milk completely if I suspect lactose intolerance?

Because milk is a good source of calcium and vitamin D, both of which are important for your well being. People who avoid milk completely may not get enough calcium from other sources, if they do not eat calcium-rich foods or do not take calcium supplement.


How is lactose intolerance managed?


1. Limit the amount of lactose you eat or drink, but complete avoidance is not necessary.

2. Hard cheeses (such as Cheddar and Swiss) and yogurt are better tolerated than a glass of milk. They are good source of proteins, calcium and vitamin D.

3. Make sure you have adequate calcium and vitamin D intake:

  • Non-dairy sources of Vitamin D include: salmon, tuna, cod, mackerel, shrimp, eggs, and milk alternatives and cereals that are fortified with Vitamin D.
  • For calcium, there are fortified juices, milk alternatives, cereals, and breads, and wholesome foods like canned salmon (with bones), tofu, broccoli, blackstrap molasses, kale, almonds, turnip greens, bok choy and seaweed


4. What is lactose-free milk?

Lactose-free milk and milk products are “pre-digested” with lactase in the manufacturing process to reduce/eliminate lactose content. They are available at most supermarkets and have the same nutritional value as regular milk and milk products.


5. What are lactase supplements?

Lactase enzyme pills (such as Digestive Advantage; Lactaid) are available to replace the missing/limited enzyme, so that lactose-containing foods can be eaten with minimal to no side effects. Check with your doctor before using these over-the-counter products as some groups, such as young children and pregnant and breastfeeding women may not be able to use them.


About the authors

John Leung, MD, is an allergist, immunologist and gastroenterologist. Leung speaks Cantonese. He can be reached at (617) 636-5333. Christianna Moran, MS and LDN, is a registered dietitian. She can be reached at (617) 636-3266. Rebecca Stanski is a dietetic intern.

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