Chances are you have lactose intolerance. You’re not alone – 5,000 years ago most humans were also lactose intolerant.
A new study published Wednesday in the journal Nature by researchers from the University of Bristol and University College London has found that people’s ability to digest lactose became common almost 5,000 years after the first signs of consumption of breast milk, which date back to around 6,000 BC.
They also found, using new computer modeling methods, that milk consumption was not the cause of increased lactose tolerance.
“The milk didn’t help at all,” study author Mark Thomas, a researcher at University College London, told DW.
“I’m excited about the statistical modeling method we’ve developed. As far as I know, no one has done it before,” Thomas said.
While breastfeeding, babies still tolerate lactose
What is lactose intolerance?
All babies can normally digest lactose. But for most of them, this ability will begin to decline after weaning from breast milk.
Today, about two-thirds of people are lactase non-persistent, which means they cannot digest lactose, the main sugar in milk.
People who are not lactase persistent cannot produce an enzyme called lactase, which breaks down lactose. When this enzyme is absent, lactose is free to travel to the colon, where bacteria feast on it.
This can cause unpleasant side effects, such as cramping, farting, or diarrhea. Together, these symptoms are called lactose intolerance.
The results of this study run counter to a widely held belief that the consumption of dairy products by our prehistoric ancestors led to the evolution of a genetic variation that allowed them to digest lactose even after adulthood. .
This hypothesis can be partly attributed to the marketing of the purported health benefits of lactose tolerance. For years dairy companies, doctors and even nutritionists have peddled milk and milk products as important vitamin D and calcium supplements and good sources of uncontaminated water.
But researchers quickly dismissed those ideas after analyzing a large pool of DNA and medical information on people in the UK. They found that whether or not they could tolerate lactose had little effect on people’s health, their calcium levels or whether or not they drank milk, Thomas said.
The global dairy industry uses around 1.5 billion cattle and was valued at nearly $830 billion (€817 billion) in 2020
Why has lactase persistence changed?
Genetic studies show that lactase persistence is “the single most highly selected genetic trait to have evolved over the last 10,000 years,” Thomas said.
Around 1000 BC. AD, the number of humans able to digest lactose, which is encoded in a gene, began to increase rapidly.
After discovering that milk consumption was not the cause of this growth spurt, the researchers tested two alternative hypotheses.
One hypothesis was that when humans were exposed to more pathogens, the symptoms of lactose intolerance combined with the new infectious agents could become fatal.
“We know that exposure to pathogens would have increased over the past 10,000 years as population densities increase, as people live closer to their pets,” Thomas said.
The other hypothesis concerned famines. When the crops sown by prehistoric lactose-intolerant populations failed, milk and dairy products became some of their only options for sustenance.
“If you’re a healthy person, you have diarrhea. It’s embarrassing. If you’re severely malnourished and you give yourself diarrhea, there’s a good chance you’ll die,” Thomas said.
The researchers used the same computer modeling methods to examine whether these insights could better explain the evolution of lactase persistence.
“And they did, much, much better,” Thomas said. “All these theories that ultimately relate to the use of milk don’t seem to help.”
The study focused primarily on European populations, and further research is needed for other continents.
Unfortunately, finding ancient DNA in African countries is trickier because it’s warmer, “and heat is a huge determinant of DNA survival,” Thomas said.