Is lactose intolerance a disease?

Evolution is not very capricious. It does not waste resources on useless things. Energy is used to search for food, to reproduce, to survive threats...

We have existed as human beings for 300,000 years. In the beginning, we were dedicated to hunting and gathering food in a nomadic life. The only milk we consumed was that given by human mothers to their children.

Human milk is 87% water, 7% sugar in the form of lactose, 5% fat, 1% protein, and other elements in smaller proportions, necessary for human babies to grow.

Lactose is a carbohydrate that is composed of two sugar molecules: glucose and galactose. In fact in Greek gála means milk, and -ose is used to name the sugars. Milk sugars... an excellent name.

Well, it turns out that our body cannot absorb lactose because those two molecules stuck together are too big to enter our intestinal cells, the ones in charge of absorbing food. Babies have a protein in their intestine called lactase (an enzyme, a lactose-scrapping protein machine) that is in charge of breaking the bond of those two molecules that form lactose, and by doing so, we can absorb glucose and galactose without a problem.

In the past, only infants drank their mothers' or wet-nursing mothers' milk. Therefore, from the 2nd to 5th year of life, they started to lose lactase because they already ate hunted meat, and wild berries (and probably insects and other Hakuna Matata-type things, now repugnant to us). They no longer needed lactase, because milking a wild animal like a bison is not only difficult but potentially deadly for the milker.

But 11,000 years ago humans began to realize that hunting and gathering wild fruits was very inefficient, and a nuisance; they began to develop agriculture and animal farming: the Neolithic began.

The first adult livestock farmers, when drinking milk from their animals, would have bloating, abdominal discomfort, and diarrhea. Nothing pleasant, as all lactose-intolerant people today know, but when hunger gets the better of you, you eat what you can. That is why adult humans began to expose themselves to the milk of other mammals as food.

At least 5 mutations occurred in this scenario, which caused the carriers (the milk mutants!!!) to have a greater tendency to maintain lactase in adulthood. This gave them an evolutionary advantage: they could nourish themselves on milk without the discomfort of non-mutant humans. One could say that they were dairy X-men and X-women.

These mutations appeared in the Middle East and Africa independently, and from there they spread with the migrations of these subjects throughout the fascinating history of mankind.

Currently, one-third of humans lose lactose over time, they do not have these mutations.

Therefore, lactose intolerance is not a disease, it is problematic in the society of the last 11,000 years in which milk is a frequent component of our diet, which has favored mutations to adapt to it, but it is not a disease.

Bibliography:

Grigorios I. Leontiadis, and George F. Longstreth. Evolutionary Medicine Perspectives: Helicobacter pylori, Lactose Intolerance, and 3 Hypotheses for Functional and Inflammatory Gastrointestinal and Hepatobiliary Disorder. Am J Gastroenterol 2022;117:721–728.

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I have not used generative artificial intelligence software (AI) to write this post. The picture has been generated with generative AI. The resemblance of the Neolithic man to the actor Pierce Brosnan is purely coincidental. 

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