Lactose intolerance

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Stomach pain, bloating, "gas" and diarrhea are all typical symptoms that many people have after eating or drinking dairy products. People who have difficulty digesting dairy products may only tolerate small amounts of lactose (a sugar found in milk and other dairy products). This is called lactose intolerance.

But some people who are sensitive to milk might actually have a different problem. It is important to get the diagnosis right before deciding to make major changes to your diet, especially in children, teenagers and people who need more calcium.

Lactose intolerance is not an allergy. This is an important difference. People who have a true milk allergy can react to even a tiny amount of dairy foods or milk. But people who are lactose intolerant can sometimes consume quite a lot of these products without having any major problems.


The symptoms usually occur shorty after drinking milk or consuming dairy products. The amount of lactose that causes symptoms varies from person to person. Symptoms may include the following: 

A bloated belly

Feeling full

Pain in the lower belly



Nausea, vomiting

Sometimes constipation too


Lactose is made up of the simple sugars glucose and galactose.

You need the enzyme lactase to break lactose down into glucose and galactose, which your body then absorbs into your bloodstream for energy.

Without sufficient lactase, lactose moves through your gut undigested and causes digestive symptoms. Still, there are multiple causes of lactase deficiency (1Trusted Source).

Here are the different types of lactose intolerance.

Primary lactose intolerance

Primary lactose intolerance — the most common type — is caused by a decrease in lactase production with age. As such, you lose the ability to absorb lactose over time (1Trusted Source, 3Trusted Source).

This form of lactose intolerance may be partially genetic since it’s more common in some populations than others.

Studies estimate that this condition affects under 10% of Northern European people, around 50% of Latin and Middle Eastern people, and 80–99% of African and Asian people (1Trusted Source).

Secondary lactose intolerance

Secondary lactose intolerance develops as a result of another condition that affects the small intestine, where lactase is produced. This is because inflammation in the wall of your gut may lead to a temporary decline in lactase production (1Trusted Source, 4Trusted Source).

Possible causes of secondary lactose intolerance include Crohn’s disease, celiac disease, chemotherapy, ulcerative colitis, and aging (1Trusted Source).

Risk factors

Increasing age. Lactose intolerance usually appears in adulthood. ...

Ethnicity. Lactose intolerance is most common in people of African, Asian, Hispanic and American Indian descent.

Premature birth. ...

Diseases affecting the small intestine. ...

Certain cancer treatments.

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Osteopenia – where you have a very low bone-mineral density. ...

Osteoporosis – where your bones become thin and weak. ...

Malnutrition – when the food you eat doesn't give you the nutrients essential for a healthy functioning body.


Choosing smaller servings of dairy. Sip small servings of milk — up to 4 ounces (118 milliliters) at a time. ...

Saving milk for mealtimes. ...

Experimenting with an assortment of dairy products. ...

Buying lactose-reduced or lactose-free products. ...

Using lactase enzyme tablets or drops.