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What Is Lactose Intolerance? Symptoms And Causes

A definition of lactose intolerance, types, causes, and treatment

Although currently there is more buzz than ever around this topic, food intolerances have always been around. Gluten and lactose allergies are the two disorders that have been making the most noise in society recently.

However, many people confuse intolerance with the potentially harmful effect that this can have on their health. To clear up this confusion, we will discuss what lactose intolerance is, its symptoms, causes, and possible treatments.

What is lactose intolerance?

Lactose intolerance is a medical condition where the affected person’s body is incapable of effectively digesting the sugar in milk. This sugar is commonly known as lactose. Although lactose intolerance is not dangerous to one’s health, its symptoms can become genuinely distressing.

Normally, these digestive problems are caused by a lactase deficiency.  Lactase is an enzyme that is synthesized in the small intestine that aids in the digestion of this sugar. So, if the affected person is deficient in this particular kind of sugar, after consuming dairy products, they could experience a series of gastrointestinal problems.

Lactose can also be found in mother’s milk and, although almost all babies are born with the ability to digest it,  cases of lactose intolerance have been found in babies and children under the age of five.

Luckily, in most of these cases, with proper treatment, people can control this disorder without having to entirely give up lactose products.

It is currently estimated that approximately  75% of the world population is lactose intolerant  to some degree, although it is true that many people simply neglect to see this due to the negative health connotations. The frequency of this disorder varies considerably depending on the area of the world that you find yourself in. The countries that make up South America, Africa, and Southern Asia are the most affected regions.

Signs and symptoms

Although it is not dangerous for the physical integrity of the affected person, lactose intolerance can cause serious digestive problems. Below are the main symptoms:

  • Abdominal bloating
  • Cramps and stomach pain
  • Gas accumulation
  • Diarrhea

Although it is less common, some people with this type of intolerance also experience nausea and/or vomiting, pain in the lower abdomen, and occasional constipation. All of the previously mentioned symptoms tend to appear shortly after consuming any lactose product.

When these foods are consumed, the lactose reaches the colon and is fermented by the intestine’s bacteria, generating fatty acid and gas accumulation. Consequentially, symptoms such as  bloating, flatulence, and pain appear.

The severity of these symptoms may vary, and this depends on the amount of lactose that the body can tolerate, as well as how much has been consumed.

Types and causes

As stated before, lactose intolerance occurs when the small intestine does not produce enough of the enzyme lactase to properly digest lactose, the sugar present in milk.

Lactase’s main function is to turn lactose into two simple sugars, glucose and galactose, which are absorbed by the bloodstream via the intestinal epithelium.

When there is a lactase deficiency, the lactose sugar is brought directly to the colon instead of being processed and absorbed.  Once it is there, the bacteria naturally present in this organ interact with the lactose causing the symptoms of this intolerance.

There are three different types of lactose intolerance which are classified depending on the lactase deficiency’s cause. These are primary, secondary, and congenital lactose intolerance.


This is the most common variation  of lactose intolerance statistically speaking.  In these cases, during the beginning of the person’s life, normal amounts of lactase are produced since this is a vital necessity for infants, but, as milk is substituted for other foods, the production of this enzyme decreases -although it tends to be enough to effectively digest lactose products.

However, a time comes when the production of lactase drops drastically in adulthood,  making lactose difficult to digest and for the body to assimilate.

In primary lactose intolerance, there is a genetic factor, which means that it is more common in families where there is at least one other affected person.


Like with many other disorders, it is possible that an illness could provoke its appearance. In this specific case, after an illness, injury, or surgical procedure, the small intestine could begin to produce less lactase.

Celiac disease, Crohn’s disease, and bacterial overgrowth are all associated with this intolerance.  The treatment of these disorders could improve the symptoms of this kind of intolerance.


Although it is uncommon, infants can be born lactose intolerant in the complete absence of lactase production. In these cases, the intolerance can be inherited, if both parents have the same kind of intolerance since this condition has a hereditary autosomal recessive pattern.

Finally, babies born prematurely can also be lactose intolerant if they have insufficient levels of lactase.


A treatment capable of improving lactase production has yet to be discovered, but there are some measures that people can take to relieve the symptoms of lactose intolerance:

  • Avoid consuming large quantities of milk or other lactose products
  • Include small quantities of lactose in meals regularly
  • Consume lactose-free foods or ones with reduced lactose
  • Add specific substances to dairy products that break down the lactose


Heaney, R. P. (2013) Dairy intake, dietary adequacy, and lactose intolerance. Advances in Nutrition, 4:151.

Leavitt, M. (2013) Clinical implications of lactose malabsorption versus lactose intolerance. Journal of Clinical Gastroenterology, 47:471.