Lactose is a simple carbohydrate composed of two molecules: one of glucose and one of galactose. It is a sugar, but it has a weak sweetening capacity. It is found in the milk of mammals (cow, goat, sheep...), as well as in the milk of nursing mothers. To be absorbed and digested, it must be cut in two (glucose/galactose) by lactase, an enzyme secreted by the cells of the small intestine. Infants and young mammals that feed exclusively on milk during the first months produce a lot of lactase. But the secretion of this enzyme by the human body tends to decrease with time whereby it is no longer produced in sufficient quantities to digest lactose properly.
If the lactose is not cut by this enzyme, it cannot be absorbed in the small intestine. It will therefore continue its way through the digestive tract and arrive in the colon where the intestinal bacteria will ferment it, creating gas production and a call for water. "It's rare that a person doesn't produce lactase at all. But when the capacity of lactase secretion is exceeded in relation to the quantity of lactose absorbed, there is malabsorption.
HOW DO YOU KNOW IF IT IS LACTOSE INTOLERANCE?
If lactose passes through the small intestine without being - or not completely - absorbed, it then reaches the colon, where it will ferment because of the specific intestinal flora of this section of the intestine. This results in swelling, pain, acid diarrhea, or vomiting in the most severe cases. The appearance of these symptoms after ingesting milk generally leads to the suspicion of lactose intolerance. However, this can be confused with an allergy to milk proteins. However, several tests can be used to confirm intolerance.
A doctor can prescribe a respiratory test that is performed in the hospital: the rate of hydrogen exhaled before and after absorption of lactose is measured, as undigested lactose is transformed into gases (including hydrogen) under the action of intestinal bacteria. As the digestive signs are common to other pathologies (celiac disease, irritable bowel syndrome, Crohn's disease...), it is important to make the right diagnosis.
CAN IT BE TREATED?
"Once the diagnosis is made, the health professional will prescribe a strict diet for one month. All foods that may contain lactose, including cheeses, ready-made meals or industrial pastries will be banned, to suppress the symptoms" says Nicolas Mathieu, gastroenterologist at the University Hospital of Grenoble. "After a month, we will try to reintroduce foods where there are traces of lactose: dry cheeses, cookies, etc. And we continue the reintroduction to find the tolerance threshold, so that the patient can have the most varied diet possible." Dr Mathieu does not recommend a lactose-free diet except in cases of intolerance. This could cause decalcification andosteoporosis. Moreover, we do not yet know the consequences that a lactose-free diet can have on the intestinal microbiota. However, if we modify the richness or variety of this flora, it seems that we favor certain diseases such as diabetes. Such a modification can induce in some patients too violent interactions with the proteins of the intestine, and lead to a chronic inflammatory bowel disease (IBD)."
WHAT IS THE DIFFERENCE WITH AN ALLERGY?
An allergy is triggered by a protein, not a carbohydrate like lactose. It is an abnormal reaction of the immune system, with the production of antibodies (IgE) and the release of histamine and other substances responsible for the allergic reaction (itching, swelling...). An allergy can have serious consequences (asthma, oedema, anaphylactic shock) whereas lactose intolerance, although it causes unpleasant symptoms, is not serious. An allergy requires the total exclusion of foods containing the allergen (the problematic protein), whereas in the case of lactose intolerance, small amounts are often tolerated. Each person must determine his or her own tolerance threshold.
>>Note: allergy to cow's milk proteins is quite common in toddlers (around 2- 3%), but disappears in 80% of cases around the age of 2.
