Lactose is a simple carbohydrate composed of two molecules: one of glucose and one of galactose. It is a sugar, but it has a low sweetening power. It is found in the milk of mammals (cow, goat, sheep, etc.), as well as in that of breastfeeding women. To be absorbed and digested, it must be split into two (glucose/galactose) by lactase, an enzyme secreted by the cells of the small intestine. Infants and young mammals that feed exclusively on milk for the first few months produce a lot of lactase. But the secretion of this enzyme by the human body tends to decrease over time. It is no longer produced in sufficient quantity to properly digest lactose.
If the lactose is not cut by this enzyme, it cannot be absorbed in the small intestine. It will therefore continue its way in the digestive tract and arrive in the colon where the intestinal bacteria will ferment it, which will create a production of gas and a call for water. “It is rare for a person to produce no lactase at all. But when lactase secretion capacities are exceeded in relation to the amount of lactose absorbed, there is malabsorption”, explains dietician Raphaël Gruman.
How do you know if it’s lactose intolerance?
If the lactose passes the small intestine without being – or not completely – absorbed, it then reaches the colon, where it will ferment due to the specific intestinal flora of this section of the intestine. The result is swelling, pain, acid diarrhea, or vomiting in the most serious cases. The appearance of these symptoms after ingestion of milk generally leads to the suspicion of lactose intolerance. However, this can be confused with a milk protein allergy. But several tests can confirm an intolerance.
“I sometimes prescribe an intolerance test by blood test (not reimbursed) to my patients, the results are quite reliable”, says the dietitian. The doctor for his part can prescribe a respiratory test which is carried out in the hospital: the level of hydrogen exhaled before and after absorption of lactosethe lactose undigested transforming into gas (including hydrogen) under the action of intestinal bacteria. Since digestive signs are common to other pathologies (celiac disease, irritable bowel syndrome, Crohn’s disease, etc.), it is important to make the correct diagnosis.
Is it curable?
Once the diagnosis is made, the health professional will prescribe a strict diet for a month. “All foods that may contain lactose, including cheeses, prepared meals or industrial pastries will be prohibited, to suppress the symptoms, says Nicolas Mathieu, gastroenterologist at the Grenoble University Hospital. After a month, we will try to reintroduce foods where there are traces of lactose: dry cheeses, biscuits, etc. And we continue the reintroduction to find the tolerance threshold, so that the patient can have the most varied diet possible. “Nicolas Mathieu does not however recommend a lactose-free diet except in cases of intolerance. This could cause decalcifications, osteoporosis, and therefore fractures. “In addition, we do not yet know the consequences that a lactose-free diet can have on the intestinal microbiota, develops Dr. Mathieu. However, if we modify the richness or the variety of this flora, it seems that we promote 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 an inflammatory bowel disease (IBD)..”
>> Namely: hard cheeses (which only contain traces of lactose) are usually not a problem. No more than yogurts, which contain lactic ferments which “predigest” the lactose, in other words, which play the role of deficient lactase. Finally, “Dairy products are generally better digested when they are cooked and incorporated into a recipe, like milk in a cake or cream in a gratin”, says Raphaël Gruman.
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 production of antibodies (IgE) and release of histamine and other substances responsible for the allergic reaction (itching, swelling, etc.). An allergy can have serious consequences (asthma, oedema, anaphylactic shock) while intolerance to lactose, 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 intolerance to lactose, small amounts are often tolerated. Everyone must determine their own tolerance level.
>>Note: Cow’s milk protein allergy is quite common in toddlers (2 to 3%), but disappears in 80% of cases around the age of 2 years.
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