Why do some people digest milk poorly

Bloating, stomach aches, and diarrhea are the lot of hot chocolate lovers whose bodies cannot digest milk. Here's why.

Why do some people digest milk poorly

What can be problematic in milk is its sugar, lactose: it contains around 5%, compared to 3 to 4% for yogurts, sour cream, or ice cream. 

To properly digest this sugar, our body must be able to manufacture the corresponding enzyme, lactase. But without its manufacturing instructions, in other words without its gene, our cells are quite incapable of producing it. However, since the distant days when we began to benefit from the milk of cows, goats, and sheep, around 10,000 years ago, this gene has been transformed.

In Asia and the Far East, for example, today only 10% of men and women have the correct version of the gene: the one which, thanks to a small mutation, allows lactose to be digested efficiently. In this part of the world, 90% of people are therefore lactose intolerant. In them, milk inevitably triggers diarrhea. This is not the case in the countries around the Mediterranean, where one in two people have the right lactase. And in central and northern Europe, where dairy has always been important, almost everyone is well equipped!

Various causes of intolerance

In France, intolerance, therefore, remains exceptional. But that doesn't mean that we all digest milk perfectly. Besides the tiny percentage of people who do not have the correct lactase, other people have an inherited abnormality: lactose passes through the lining of their stomach and, once in the blood, this sugar can poison the body. 

Another concern, the most common cause of intolerance in newborns: certain diseases weaken the lining of the intestine and thus interfere with the digestion of milk. It could be infected with viruses, bacteria or parasites, inflammatory disease, allergies, reactions to drugs, etc. The problems go away as soon as the disease is cured.

Digestion more difficult with age

The fact remains that in mammals that we are, the lactase enzyme becomes less active when we are young. In adolescence or adulthood, this efficiency can decrease by 90%, making it difficult to digest lactose. But this sensitivity varies in its symptoms from person to person. Some suffer from bloating and diarrhea as soon as they swallow a small glass of milk, others only react after consuming too much.

In addition, the sensitivity is more or less strong depending on the dairy products: skimmed milk is less well tolerated than whole milk, to which we are generally more sensitive than to milk preparations, which pass through the stomach more slowly. Let us add that yogurts have bacteria on their side which predigest lactose. And that ripened cheeses have very little lactose, the draining having removed part of it, and the bacteria the rest.

Finally, as Francis Raul, Research Director at Inserm, emphasizes, "the presence of other foods reduces or eliminates any difficulty in absorbing lactose". For those for whom dairy products are really a source of inconvenience, it is, therefore, better to avoid consuming them on an empty stomach. Without depriving yourself, because they are useful sources of calcium. Even if, fortunately, nature does things well: by a compensatory mechanism, those who consume less calcium are able to absorb it more efficiently.

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