Are humans meant to drink milk? Yes and no. Breastfed babies live on a diet of nothing but milk, but once they move onto solid foods they become lactose intolerant, according to a paper published in PLoS Computational Biology.
The enzyme that’s meant to digest milk is called lactase and in the majority of the global population, the human body stops producing it after an infant is finished breastfeeding. Without an enzyme to break down milk, it sits in the colon and ferments, creating gastrointestinal turmoil. Being lactose intolerant can mean gas, bloating, cramping, flatulance, and nausea.
Around 90 percent of Americans and northern Europeans have a gene mutation that causes lactase to keep working into adulthood, meaning they don’t become lactose intolerant. But that’s not the case in the rest of the world where 60 percent of the population can’t digest milk. In fact, globally only 5 percent of Asians can digest it, that’s why it isn’t a part of their diet. And only 25 percent of Africans and 50 percent of Mediterraneans (France, Spain, Italy, Greece, Portugal, Turkey, Syria, Lebanon, and Israel) can digest dairy.
Lactose intolerance is not an allergy because it’s not the immune system that causes the reaction, rather, it’s an enzymatic response. Scientists contend that lactose intolerance isn’t a disease either. It’s a gene mutation that allows us to tolerate lactose past infancy. That’s why in the scientific community, it’s referred to as lactase persistence or the ability of the enzyme lactase to persist into adulthood.
Why can Americans and northern Europeans digest milk when other ethnicities cannot? It’s likely related to an evolutionary change that happened when we started raising cows for milk, according to the study.
According to Nature: “[L]actase persistence is strongly correlated with the dairying history of the population. This genetic ability to digest milk has been regarded as a classic example of gene-culture co-evolution, where the culture of dairying creates a strong selective advantage to those who can drink milk as adults, for only they can nutritionally benefit from the milk.”
This genetic mutation started showing up about 7,500 years ago when bovine production made drinking the milk of other mammals possible. Prior to dairy production there was really no other access to milk in the first place and therefore, no need to be able to digest it. Once children were done breastfeeding they would no longer have exposure to it.
So if you’re wondering whether dairy must to be a part of a healthy diet, this may help to answer your question. Our ancestors from 7,000 years back didn’t drink milk beyond infancy and today much of the world still doesn’t drink it.
But for those who acquired the gene mutation, it not only allows us to drink milk but sample all of its offspring including stinky cheeses, ice cream, yogurt, cottage cheese, buttermilk, and cream.
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Image of ice cream from Shuttershock