What is lactose intolerance?

Lactose intolerance is an intestinal condition in which the body produces little or no lactase enzyme. enzyme lactaselactase enzyme, which is responsible for digesting lactose (the natural and major sugar in milk) and separating it into its constituent monosaccharides (glucose and galactose).

Thus, when the absence of lactase causes lactose malabsorption, it cannot be absorbed in the intestine, producing a clinical digestive condition known as lactose intolerance.

Symptoms

The most frequent symptoms associated with lactose intolerance are:

• Abdominal pain or cramps
• Flatulence
• Diarrhea
• Abdominal distention

However, non-specific and atypical symptoms such as headaches, tiredness, concentration or sleep disturbances, nervousness or pain in the extremities may also appear.

Types of lactose intolerance

• Congenital lactase deficiency: this is a genetic alteration and is inherited. It is due to the absolute absence of lactase due to mutations in its gene, and is manifested from the first day of life. It is an extremely rare disorder. The only possible treatment is to avoid lactose intake from birth.
• Primary intolerance (persistent): this is the most common form and is due to a natural decrease in lactase activity that occurs with age, especially when dairy products are no longer consumed. It appears mainly in adulthood and its treatment consists of reducing lactose intake to amounts that do not cause symptomatology, which can be complemented with the administration of exogenous lactase. Complete exclusion of lactose is not usually necessary, since most patients can tolerate small amounts of lactose in each intake.
• Secondary intolerance (non-persistent): this is an acquired condition, caused by gastrointestinal diseases (gastroenteritis, infections, vascular disease, bacterial overgrowth, etc.), intestinal resections, drugs that can affect the intestinal mucosa (NSAIDs, antibiotics, chemotherapy), or chronic diseases of the small intestine (celiac disease, inflammatory disease, diabetic enteropathy, etc.). These aggressions reduce the lactose hydrolysis capacity. It is generally a reversible situation in which increasing doses of lactose are reintroduced without causing symptoms.

Diagnosis

There are 5 techniques used to diagnose lactose intolerance:

• Exhaled-air test: this is based on the measurement of the concentration of_{H2 and} CH4 gases exhaled with the breath after administration of a small amount of lactose (25 g). In subjects with lactase deficiency, the lactose that is not absorbed by the intestine is fermented by the bacteria in the colon, which produce a large amount of these gases. It is the most common test because it is non-invasive, simple, highly sensitive and specific.
• Lactose tolerance test: the aim is to evaluate the glycemic response after a lactose overload (50 g). Blood samples are taken at a 2-hour interval to measure the increase in glucose. In a normal situation, an increase in blood glucose indicates that lactose is being hydrolyzed and absorbed in the small intestine, so the absence of this glycemic increase would indicate a lactase deficiency. It is a rather non-specific test since certain diseases can invalidate the result.
• Gaxylose test: in this case, the patient ingests a drink rich in gaxylose, which is metabolized in the small intestine by lactase. Subsequently, the patient's urine is collected for 5 hours, where the presence of one of the gaxylose metabolites is measured.
• Small intestine biopsy: consists of the extraction of a sample of mucosa from the small intestine and its subsequent analysis to examine possible alterations that may affect the metabolization and/or absorption of lactose. To do this, an endoscope is introduced through the mouth to take the sample to be analyzed. However, this is a very invasive test and the samples taken may not reflect the overall activity of the intestine.
• Genetic analysis: a regulatory gene of the lactase gene and the polymorphisms that cause the pathology are analyzed by extracting a blood or oral mucosa sample. It is only useful for the diagnosis of congenital hypolactasia.