Everything You Need to Know About Lactose Intolerance

· July 26, 2018
In this article, learn everything you need to know about lactose intolerance, including its causes and symptoms.

Lactose intolerance is a common disorder in adults, characterized by a decreased ability to digest this sugar. Since the body can’t digest it, the lactose irritates the intestinal mucosa, causing diarrhea. Lactose intolerance is a malabsorption syndrome.

There are many degrees of intolerance, ranging from mild to major discomfort and intestinal damage.

Absorption of Lactose

lactose intolerance

Lactose is a disaccharide, a carbohydrate made up of two monosaccharides: glucose and galactose. Dairy foods contain this nutrient. Then, your body absorbs it at the molecular level in your intestinal cells, or enterocytes.

These cells have a cubic shape and microvilli in the part that comes into contact with the intestinal lumen.

The microvilli form an irregular surface known as the brush border. This area is where most of the nutrients are absorbed.

Some nutrients must be broken into simpler molecules to be absorbed and enter the bloodstream, as is the case of lactose. The lactase must divide itself into a molecule of glucose and another molecule of galactose so lactose can be absorbed.

Lactase is an enzyme located in the brush border of the enterocytes which is distributed unevenly through the digestive tract. It’s most abundant in the first sections of the small intestine, the duodenum and jejunum.

Lactase is at its peak during late pregnancy and lactation. After that, it decreases its activity.

In some ethnic groups, lactase expression decreases by the time they reach adulthood. However, in Caucasians, it never stops.


When your body doesn’t make this enzyme, it doesn’t absorb lactose. As a result, lactose reaches the colon, where the bacterial flora ferments it. There, it produces large amounts of hydrogen and irritates your gastrointestinal mucosa. This changes your digestion, causing gastroenteritis.

Take a look at this article: Which Dairy Products Contain the Least Lactose?

Pathogenesis of Lactose Intolerance

a man with lactose intolerance

From a pathogenic standpoint, there is a lack of lactase due to two reasons. First, it is either because the enzyme isn’t synthesized, or it is due to a bowel disease.

Primary Lactase Deficiency

First of all, primary lactase deficiency is the most common cause of lactose intolerance worldwide. It’s isolated and not caused by any other disease.

In this case, the body doesn’t synthesize the enzyme due to various causes:

  • Congenital lactase deficiency. In this case, it’s a hereditary disease, the enzyme isn’t synthesized due to a genetic defect. Both parents need to have the mutation for the child to have it. This means it follows a recessive pattern. It’s rare, but these children don’t synthesize any lactase, so they don’t tolerate dairy foods from birth.
  • Developmental lactose intolerance may occur in premature infants. This is especially the case for those born before 32 weeks because the enzyme has not yet reached its peak.
  • Physiological deficiency. We already mentioned that lactase synthesis decreases progressively after breastfeeding. Actually, it’s very common in African and Asian individuals. This intolerance appears at different ages. It’s often quite early in these ethnicities, around the age of 5. The incident of this deficit is lower in the Caucasian population and usually becomes apparent in older ages.

Secondary Lactase Deficiency

In these case, lactose intolerance is due to a change in the intestinal mucosa due to other reasons. Depending on the cause, the lactose intolerance may be permanent or reversible after treating the causative pathology.

In addition, it may be due to microvilli changes. These prevent normal carbohydrate absorption. This is the case of inflammatory diseases such as Crohn’s disease or ulcerative colitis.

Plus, italso occurs in intestinal infections that alter the digestive tract lining, especially in children.

Symptoms of Lactose intolerance

symptoms of lactose intolerance

As a result of lactose intolerance, after consuming dairy products the intestinal irritation will cause:

  • Gas
  • Nausea and vomiting
  • Pain and bloating
  • Watery diarrhea, due to osmosis.

The severity of the symptoms may vary depending on the degree of intolerance. There are people who can’t tolerate milk but can tolerate other dairy products such as cheese or yogurt. In many cases, the symptoms are mild and most people can tolerate small amounts of milk.

When the deficit is congenital or appears in the early stages of development, children may suffer a significant developmental delay. In these cases, the consequences can be severe.

Want to know more? Read: Nutritious, gluten free, lactose free oat muffins

Diagnosis of Lactose Intolerance

dairy products

People may suspect they suffer from lactose intolerance due to gastrointestinal symptoms that come with milk consumption.

However, there are different tests that can be used to confirm primary lactase deficiency:

  • Lactose tolerance test. If you digest lactose properly, your glucose levels should rise after consuming it. In this test, the patient has to drink some lactose and take a blood sugar test afterward. If the patient’s glucose level doesn’t increase at least 20 md/dL, they have lactose intolerance.
  • Hydrogen breath test. As we mentioned above, the bacterial fermentation of lactose produces a lot of hydrogen in the colon. The gas enters the bloodstream and reaches the lungs, where you expel it. This is why it may be useful to measure the hydrogen in the breath of a person who ingested lactose. Larger than normal amounts of exhaled hydrogen mean that the subject doesn’t absorb lactose well.
  • Stool acidity test. Your body eliminates some of the hydrogen produced in yoyr stool, which lowers its pH and makes it acidic.

If these tests are abnormal, this may mean the person has lactose intolerance.

Most cases of lactose intolerance aren’t serious. Fortunately, you may reverse your symptoms by decreasing the amount of lactose in your diet.