lactose intolerance

Lactose intolerance is a condition in which some persons have digestive symptoms such as bloating, flatulence and diarrhea after consumption of foods and drinks that contain lactose. Lactose is a sugar that is naturally found in milk and milk products (such as cheese or ice cream).

The digestive symptoms of lactose intolerance are caused by lactose malabsorption. Lactose malabsorption occurs when small intestines cannot digest the lactose present in milk and milk products due to deficiency or absence of lactase enzyme.

Congenital lactase deficiency, also called congenital alactasia, is a disorder in which infants are unable to break down lactose in breast milk or formula milk. This form of lactose intolerance results in severe diarrhea. Lactose intolerance in adulthood is caused by reduced production of lactase after infancy (lactase nonpersistence).

Most people with lactose intolerance can tolerate some amount of lactose without having symptoms. Different people can tolerate different amounts of lactose before having symptoms. As much as 60 percent of the world's population is unable to process the lactose in animal milk.

Lactose intolerance is different from milk allergy, as milk allergy is an immune system disorder.



Symptoms of lactose intolerance may be noticed within a few hours after ingestion of milk or milk products or other foods that contain lactose. Symptoms usually appear with in 30 minutes to two hours after lactose intake. These symptoms may include-

  • Bloating
  • Flatulence
  • Diarrhea
  • Nausea
  • Vomiting
  • Pain in abdomen
  • stomach “growling” or rumbling sounds
  • Feeling sick
  • Urgency with bowel movements



Normally lactose (milk sugar) breaks down by lactase in the small intestine in to two simple sugars glucose and galactose, which are absorbed into the bloodstream through the intestinal lining. Lactase is an enzyme which helps in the process of digestion of lactose.

When the small intestine has deficient or low levels of lactase enzymes, lactose is not properly digested and the undigested lactose passes into the colon (large intestine). Bacteria present in the colon break down the lactose and create fluid and gas. In some people, this extra fluid and gas causes symptoms of lactose intolerance.

Lactase deficiency may be of two types:

(i)Primary lactase deficiency: In this type of lactase deficiency genes play an important role, such as:

  • Congenital lactase deficiency: It is a rare condition, in this the small intestine makes little or no lactase since birth. This form of lactose intolerance results in severe diarrhea.
  • Lactase non-persistence: In this, the small intestine makes less lactase after infancy and it gets lower with age. Symptoms of lactose intolerance may not begin until later childhood, the teen years, or early adulthood.

(ii)Secondary lactase deficiency: As not all cases of lactose intolerance are genetic, the following conditions can also lead to lactose intolerance:

  • Injury to the small intestine due to infectious disease or other conditions may cause lactose intolerance such as Rotavirus and Giardia infections. Secondary lactase deficiency can also occur in celiac disease, Crohn’s disease.
  • Premature birth: In premature babies the small intestine may not make enough lactase for a short duration of time after birth but as baby gets older the small intestine usually makes more lactase.

(iii)Acquired Lactase Deficiency: Many individuals acquire lactose intolerance as they get older. This condition is due to a normal decline in the amount of the enzyme lactase present in the small intestine as age increases.



For diagnosis of lactose intolerance, health care provider may ask about symptoms, family and medical history, eating habits and do physical examination.

Other conditions such as irritable bowel syndrome, inflammatory bowel diseases can cause symptoms similar to those of lactose intolerance. Health care provider may ask the person to stop eating and drinking milk and milk products for a period of time to see if the symptoms are still present there or not. If symptoms are still there, additional tests may be done.

Hydrogen breath test

For this test, person drinks a liquid that contains a known amount of lactose. Every 30 minutes over a few hours, person will breathe into a balloon-type container that measures the amount of hydrogen in your breath. If breath hydrogen levels and symptoms increase during the test, doctor may diagnose lactose intolerance.



Symptoms of lactose intolerance can be managed by change in diet; to limit or avoid foods and drinks that contain lactose such as milk and milk products. Some persons can manage their symptoms by just limiting the intake of lactose while others may need to avoid lactose altogether.

Treatments depend on the cause of lactose intolerance. If lactose intolerance is caused by lactase non persistence or congenital lactase deficiency change in diet can manage the symptoms.

Some milk and milk products can be tolerated if taken in a following way:

  • drink small amounts of milk at a time and have it with meals,
  • add milk and milk products to your diet a little at a time and see how you feel,
  • try eating yogurt and hard cheeses, like cheddar or Swiss, which are lower in lactose than other milk products,
  • use lactase products to help digest the lactose in milk and milk products. Lactase products are tablets or drops that contain lactase, the enzyme that breaks down lactose. Some people, such as young children and pregnant and breastfeeding women, may not be able to use them.
  • Use of lactose-free and lactose-reduced milk and milk products

If an individual is restricting their milk/ dairy intake it is important to ensure adequate supplementation of calcium and vitamin D in the diet. This is especially important for pediatric patients and women.

Following sources are not containing lactose bur are rich sources of calcium.

  • fish with soft bones, such as canned salmon or sardines
  • broccoli and leafy green vegetables
  • oranges
  • almonds, Brazil nuts, and dried beans
  • tofu
  • products with labels that show they have added calcium, such as some cereals, fruit juices, and soy milk

Ingredients can be checked on packaged foods to see if the product contains lactose. The following words mean that the product contains lactose:

  • milk
  • lactose
  • whey
  • curds
  • milk by-products
  • dry milk solids
  • nonfat dry milk powder

If lactose intolerance is caused by an injury/infection to small intestine, it can be treated accordingly. While in premature babies if they are lactose intolerant, the condition usually improves without treatment as the baby gets older.



If diet is not sufficient in calcium intake and other vitamins and minerals, following complications can be found in person with lactose intolerance:

  • Osteopenia-low mineral density in bones
  • Osteoporosis-Thin and weak bones, more susceptible to fractures
  • Malnutrition due to poor intake of nutrients




  • PUBLISHED DATE : Jun 21, 2019
  • CREATED / VALIDATED BY : Dr. Aruna Rastogi
  • LAST UPDATED ON : Jun 21, 2019


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