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Image: “Blue Cheese” by cookbookman17. License: CC BY 2.0


Definition of Lactose Intolerance

Lactose intolerance is a digestive disorder which prevents the body from digesting lactose, a type of sugar found in milk and milk products.

Pathophysiology of Lactose Intolerance

Lactose intolerance is caused by a deficiency of the enzyme lactase. The enzyme cleaves the disaccharide lactose in the small intestine. Lactase is essential for the digestion of lactose because the intestine can absorb sugar molecules only in the form of monosaccharides.

Hydrolysis of lactose

Image: “Hydrolysis of lactose,” by Yikrazuul. License: public domain

Many people have lactose intolerance, which is caused by a lack of lactase when the mucosal cells of the small intestine are unable to produce sufficient amounts of lactase. Lactase has a strong osmotic effect and causes diarrhea. If lactase enters the colon, it is cleaved by intestinal bacteria. The process produces gases, which lead to flatulence.

Note: Lactose consists of two monosaccharides: glucose and galactose.

Epidemiology of Lactose Intolerance

Many people worldwide have lactose intolerance due to a gradual decrease in the enzyme activity of lactase after breastfeeding, which can lead to primary lactose intolerance. The prevalence of lactose intolerance significantly increases from northern to southern Europe. About 2% of the Scandinavian population has lactose intolerance, whereas 2 of 3 people are affected in Italy.

Depending on ethnic background, 15%–80% of people in different population groups are affected in the United States. The overall rate of people with lactose intolerance in the United States is estimated to be 25%.

Lactose intolerance in the world

Image: “Laktoseintoleranz-1,” by Rainer Z. License: public domain

Congenital lactose intolerance is very rare in healthy infants. Very few infants are born with alactasia, which involves an inability to tolerate the mother’s milk, which contains lactose. Such infants develop serious diseases if not treated in time.

Etiology of Lactose Intolerance

Lactose intolerance has primary and secondary causes. Primary causes are either hereditary (rare) and present from birth or due to continuously decreased activity of lactase after infancy. The latter type of lactose intolerance is called adult lactase deficiency.

Secondary types are caused by gastrointestinal diseases due to injuries of the mucosa of the small intestine. Secondary lactose intolerance can be caused, for example, by celiac disease, enteritis, immunoglobulin A deficiency, or short bowel syndrome.

Symptoms and Pathology of Lactose Intolerance

Symptoms occur within an hour of consumption of food containing lactose.

Complaints correlate with amount of consumed milk products

Lactose intolerance frequently manifests itself in childhood and adolescence; however, secondary types can occur at any age.

Undigested lactose enters the colon directly via the small intestine. Subsequently, the lactose is fermented by bacteria, which produces gases (hydrogen and carbon dioxide) and causes the following symptoms:

  • Strong spastic flatulence
  • Abdominal cramps/pain
  • Bloating
  • Diarrhea

Lactose has strong osmotic effects and binds water. The process results in increased water flow from the tissue inside the colon, which causes more fluid stools and acceleration of the vermicular movement of the intestine, leading to diarrhea.

Symptoms can be very mild or very severe, and sever symptoms might require medical help.

Diagnosis of Lactose Intolerance

Recognizing lactase deficiency

A commonly used examination for diagnosis of lactose intolerance is the hydrogen breath test. Only a little hydrogen can be detected in the breath of people with sufficient amounts of lactase.

Hydrogen is one of the gases formed in the bacterial fermentation process of undigested lactose in the colon. Hydrogen is reabsorbed by the intestine and transported via the bloodstream to the lungs, then exhaled.

Some people self-diagnose lactose intolerance via diet tests or exposure tests; however, such tests are not as clear as the hydrogen breath test. If an affected person refrains from eating products rich in milk and observes no symptoms during that time, he or she can assume lactose intolerance. The person can confirm lactose intolerance with the following exposure test: Drinks a glass of water containing dissolved lactose. After a few hours, if the aforementioned symptoms are observed, then lactose intolerance if confirmed.

Note: For examinations, only the hydrogen breath test is relevant in diagnosis.

Therapy of Lactose Intolerance

The most useful therapy is to refrain from consuming lactose. Every patient can test his or her own tolerance limits during that process.

Those suffering from lactose intolerance can use food supplements such as lactase pills, which aid the digestion of lactose. However, such patients should still try to adhere to lactose-free nutrition when possible.

Note: Nonpasteurized yogurt contains enough bacterial lactase and can, therefore, be consumed.

Prevention of Lactose Intolerance

Thorough repair of the intestinal flora, as well as abstinence from milk products, supports the regeneration of intestinal mucosa and promotes the formation of new, healthy intestinal mucosal cells.

People suffering from lactose intolerance should pay attention to industrially produced foods and other products, which may contain hidden lactose. Most people tolerate small amounts of lactose (e.g. medicines containing lactose, ripe cheese).

Alternative Foods for Lactose Intolerant Patients

Calcium is a very important mineral required by the body. Because calcium is found in milk and milk products, patients with lactose intolerance must meet their calcium requirements from alternative sources, such as:

  • Vegetables: okra; kale; and other green, leafy vegetables
  • Fish
  • Calcium-fortified juices and cereals
  • Calcium-fortified soy milk and other soy products
  • Nuts such as almonds

Complications of Lactose Intolerance

If a patient lactose intolerance develops calcium deficiency, the following complications may occur:

  • Weight loss
  • Diseases due to malnutrition, such as rickets and osteomalacia
  • Short stature
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