Lactose is a sugar present in milk and milk products. The small intestine produces a digestive enzyme called lactase, which is necessary to digest, or break down, lactose into simpler absorbable forms of sugar, glucose and galactose. INTOLERANCE


Lactose intolerance is a group of symptoms, such as nausea, bloating, diarrhea and gas, that results after consuming milk or milk products. The symptoms typically occur 1/2 hour to 2 hours after the consumption of dairy. Lactose intolerance happens when there is a lack or reduced levels of lactase enzyme in the small intestine. In individuals with lactase deficiency, there is lactose maldigestion and malabsorption, i.e., lactose is neither digested nor absorbed in the small intestine, and undigested lactose passes to the colon (large intestine) where it is broken down by the bacteria producing liquid and gas. The severity of symptoms depends on the amount of lactose consumed. In fact, many people with lactase deficiency are able to tolerate small amounts of lactose. While lactose intolerance is not dangerous, its can cause discomfort and distress.


There are four types of lactase deficiency that can lead to lactose intolerance.

Primary lactase deficiency (also known as lactase non-persistence) is the most common type. In this condition, lactase production diminishes over time. This decline usually begins at about 2 years of age. Children with this type of deficiency may not have any symptoms until late adolescence or adulthood. This appears to be genetically inherited.

Secondary lactase deficiency results from injury to the small intestine such as infection, disease, trauma or surgery. Luckily, the lactose intolerance in this situation is often temporary and the symptoms improve as the intestine heals.

Developmental lactase deficiency may occur in premature infants. This condition typically lasts only for a short time after birth.

Congenital lactase deficiency is extremely rare where in the small intestine produces little or no lactase from birth.


The vast majority of those affected develop lactose intolerance over time as the body’s production of lactase declines. The rate is even higher in Asians at about 90%. Only 15-20% of Caucasian Americans tend to be lactose intolerant.


The diagnosis is based on medical, family and diet history and a review of symptoms as well as physical examination and tests. however, many conditions, such as irritable bowel syndrome, celiac disease and other malabsorption disorders and inflammatory bowel disease, can cause similar symptoms.

Trial elimination of lactose

Generally eliminating lactose products from the diet for a short period to see if the symptoms resolve themselves is a quick and inexpensive way to confirm the problem.

Hydrogen breath test

This test measures the amount of hydrogen in a person’s breath. In normal individuals, only a small amount of hydrogen is detectable in the breath; however, in those with lactose intolerance the undigested lactose produces high levels of hydrogen (due to bacterial break down of the milk sugar in the colon).

Stool acidity test

Consequently the stool in lactose intolerant individuals is acidic after the consumption of lactose.


Most people with lactose intolerance can tolerate some amount of lactose in their diet and do not need to eliminate milk or dairy products completely. Avoiding milk and milk products completely may keep people from getting their required amounts of calcium and vitamin D. There is individual variation of how much lactose one can tolerate. Generally speaking, most people can tolerate at least 12 grams of lactose (1 cup of milk) in one sitting with no or minimal symptoms. They may be able to better tolerate lactose consumption with meals or in smaller amounts throughout the day.

Yogurt and cheeses

A 1.5-oz serving of low-fat hard cheese has less than one gram of lactose where as one cup of low-fat milk has 11-13 grams of lactose. Low-fat milk, though, cannot be substituted for regular milk for lactose intolerance purpose as it has the same lactose as regular milk, only the fat content is lower.

Lactose-free and lactose-reduced milk and milk products

These are widely available in supermarkets. They are identical nutritionally to regular milk products and can be used in place of regular dairy by lactose intolerant individuals.

Lactase products

These are not suitable for young children or pregnant and breast feeding women.

Non-dairy milk and milk products

There is a wide variety of plant-based milk and milk products available in the marketplace including soy milk, almond milk, hazelnut milk and coconut milk. Generally there is less calcium and vitamin D in these products and one should look for products that are fortified.

By S Murthy Badiga, MD, FACG

Website | + posts