What is Lactose Intolerance?

By Dr. Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

Lactose intolerance describes a condition where a person is incapable of digesting lactose - a type of sugar present in milk and dairy products. Food intolerance is different from food allergy. While symptoms of allergy may be brought about by consuming even tiny amounts of a certain food, the amount that brings about the symptoms of intolerance varies from person to person.

Symptoms of lactose intolerance

People with lactose intolerance usually develop symptoms when they consume milk or milk products such as cheese, yoghurt and butter. Symptoms include:

• Diarrhea
• Nausea and vomiting
• Bloated abdomen
• Increased flatulence

Causes of lactose intolerance

Normally, lactose present in milk and dairy products is broken down by an enzyme called lactase that is present in the digestive system. This enzyme breaks lactose down into two simple sugars, glucose and galactose, which can then be easily absorbed into the blood stream and utilized by the body.

However, people with lactose intolerance have deficient levels of lactase meaning that much of this lactose sugar remains in the gut without being absorbed. The lactose is then fermented by bacteria inside the gut and this leads to the formation of gas causing bloating and flatulence. The fermented lactose also irritates the inner walls of the gut causing nausea, vomiting and diarrhea.

Diagnosis and treatment of lactose intolerance

Lactose intolerance cannot be diagnosed based on clinical features and symptoms alone and requires a breath or blood test to assess how a person processes lactose. There is a large number of people who misdiagnose themselves as lactose intolerant. Cow milk allergy is also often mistaken for lactose intolerance.

Treatment involves avoiding all milk and milk products. Most people with lactose intolerance may be assessed for their calcium and vitamin D as these are usually obtained from milk and milk products, so may need supplementing in the diet. Calcium and vitamin D are essential for healthy bones and teeth. Some individuals may benefit from lactase enzyme substitutes.

Further Reading

• All Lactose Intolerance Content
• Lactase Biology
• Lactose Intolerance Diagnosis
• Managing Lactose Intolerance
• Lactose Intolerance History