Lactose and lactose intolerance
Lactose is a disaccharide consisting of glucose and galactose, and is the primary sugar in the milk of mammals. Once ingested, is hydrolyzed by lactase, an enzyme present on the membrane of intestinal microvilli in its components, glucose and galactose, which are then absorbed. If activity is reduced or absent lactase, undigested lactose intolerance can cause symptoms such as abdominal pain, bloating, flatulence and diarrhea. Lactose intolerance should not be confused with allergy to milk protein, which can not be solved by using the free milk lactose.
Those are instead suffering from galactosemia, an inherited disorder of galactose metabolism, not only do not tolerate lactose, but more severe symptoms than those observed in subjects with lactose intolerance.
primary lactase deficiency is genetically determined. In the case of congenital deficiency of lactase (lactase deficiency Congenital , CLD), we have a very severe lactase deficiency, whose activity is very low or absent at birth. In contrast, adult lactase deficiency, also referred to as lactase non-persistence ( Lactase-nonpersistence , LNP), is a normal developmental phenomenon characterized by the down-regulation of lactase activity, which occurs soon after weaning in most ethnic groups. The frequency of the LNP in adults ranges from 4 to 56%, with a lower prevalence in the countries of northern Europe and is more prevalent in southern countries. In adults with LNP, the undigested lactose reaches the colon where it is degraded to lactic acid, acetic acid, hydrogen and carbon dioxide by intestinal bacteria, with symptoms described above. However, the maldigestion of lactose leads to symptoms of intolerance in all the LNP subjects.
It should be noted also that the lactase is an enzyme whose activity is not induced by the substrate, ie the presence of more or less abundant to digest lactose. Nevertheless, it is shown that the daily consumption of lactose can result in an adaptation of the intestinal flora, thus reducing the symptoms related to lactose maldigestion.
Other forms of this disaccharide intolerance, are represented by lactase deficiency secondary to other conditions, as in the case of small bowel diseases that cause a rate to epithelial tissue. Also the acute gastroenteritis, celiac disease is not treated, chronic intestinal diseases and cancer chemotherapy may be associated with lactase deficiency.
The most commonly used test to measure lactose digestion have the breath test and lactose tolerance test. The first measurement at different time intervals, the amount of hydrogen contained in the breath of an individual who was given a drink containing lactose. The hydrogen comes from the fermentation by intestinal bacteria consumed the sugar and undigested. The lactose tolerance test, is based instead on the measurement of plasma glucose after ingestion of a beverage containing lactose. The test is based on the fact that if the lactose is not digested, there is a rise in blood sugar after his appointment. This test has a variability greater than the breath test and is therefore less reliable. The combination of the two tests can greatly improve the diagnosis, although a fee equal to 5% of intolerances, however, would not be diagnosed except by an intestinal biopsy is associated with the measurement of lactase. The analysis of the lactase gene polymorphisms may eventually add useful information.
Regarding therapy, the only satisfactory treatment for lactose intolerance is the diet reduced the content of this sugar. Pharmaceutical products that contain the enzyme lactase may be a good support, especially when meals are eaten out of cases and are not sure of the real absence of lactose consumed dishes. Unfortunately, there are currently no harmonized rules at European level to define a product free of lactose. The only regulation is set by Directive 2006/141/EC, which provides that formulated for babies and food formulas may be the definitive "lactose-free" when they contain less than 10 mg of lactose per 100 kcal. To this add after the fact that the lactose tolerance is highly variable among individuals who do not tolerate: the majority of individuals diagnosed with lactose intolerance or maldigestion can tolerate 12 g of this sugar as a single dose (especially if taken with food) in the absence of symptoms or with minor effects. A ome individuals are able to tolerate 20 to 40 g of lactose per day, when taken with other nutrients. The consumption of 50 g of lactose per day, however, induces symptoms in the vast majority of the intolerant. In some individuals, symptoms of lactose intolerance have been reported after taking less than 6 g of lactose.
The prevalence of lactose intolerance is usually very low in young children and remains low in adulthood among individuals of northern European origin, which tolerate this better than sugar.
