Everything we thought about the origin of lactose tolerance is wrong, says a study Science In-depth report on science and technology DW

You have lactose intolerance. You’re not alone – 5,000 years ago, most people were lactose intolerant.

A new study published Wednesday in the journal Nature by researchers from the University of Bristol and University College London found that people’s ability to digest lactose became widespread nearly 5,000 years after the first signs of human milk consumption.

They also used new computer modeling techniques to find that milk consumption did not cause lactose intolerance.

“Milk didn’t help at all,” researcher Mark Thomas of University College London told DW.

“I’m very excited about the statistical modeling approach we’ve developed. As far as I know, no one has done this before,” said Thomas.

Breastfed babies are still lactose intolerant

What is lactose intolerance?

All children can digest lactose. However, most of them lose this ability after breastfeeding.

Today, about two-thirds of people are lactase intolerant, meaning they cannot digest lactose, the main sugar in milk.

People with persistent lactase cannot produce an enzyme called lactase, which breaks down lactose. Without this enzyme, lactose is free to travel to the large intestine, where bacteria feed on it.

This can cause unpleasant side effects, such as cramping, vomiting or diarrhea. These symptoms together are called lactose intolerance.

surprising results

The results of this study contradict the widely held belief that our prehistoric ancestors’ consumption of dairy products led to the evolution of a genetic variation that allowed them to digest lactose well into adulthood.

This assumption can be traced in part to the marketing of the supposed health benefits of lactose tolerance. For years, dairy companies, doctors, and even nutritionists have marketed milk and milk as important supplements of vitamin D and calcium, and as a good source of clean water.

But researchers quickly dismissed those ideas after analyzing a large set of DNA and medical data from people in the UK. They found that whether people were lactose intolerant had little effect on their health, their calcium levels, or whether they drank milk or not, Thomas said.

Cows are milked while riding a slow-motion carousel in Chestertown, Maryland, USA

The global dairy industry employs approximately 1.5 billion cattle and is estimated to be worth approximately $830 billion (€817 billion) in 2020

Why did lactase resistance evolve?

Genetic studies have shown that lactase resistance is “the most strongly selected single gene trait that has evolved over the past 10,000 years,” Thomas said.

Around 1000 BC, the number of people able to digest lactose, encoded by a single gene, began to increase rapidly.

After learning that milk consumption was not behind this increase, the researchers tested two alternative hypotheses.

One hypothesis was that when people were exposed to more pathogens, symptoms of lactose intolerance and new infectious agents could lead to death.

“We know that exposure to pathogens has increased over the last 10,000 years as population density has increased, as people have lived closer to domestic animals,” Thomas said.

Another hypothesis was related to starvation. When the crops grown by lactose-tolerant prehistoric populations failed, milk and dairy products became one of their only options for nutrition.

“If you’re a healthy person, you’re going to have diarrhea. It’s a shame. If you don’t eat a lot and you give yourself diarrhea, there’s a good chance you’re going to die,” Thomas said.

The researchers used the same computer modeling techniques to test whether these ideas could better explain the evolution of lactase resistance.

“They did better,” Thomas said. “In the end, all these theories about using milk didn’t help.”

The study focused mainly on the European population and more research is needed for other continents.

Unfortunately, it’s harder to find ancient DNA in African countries because it’s hot, “and heat is a big factor in DNA survival,” Thomas said.

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