People and carbohydrates: a complex relationship dating back 800,000 years

Trying to limit your carb intake means going against almost a million years of evolution.

Humans are among the few species that have multiple copies of certain genes that help us break down starch – carbohydrates like potatoes, beans, corn and grains – so we can turn it into energy our bodies can use.

However, it has been difficult for scientists to determine when in human history we acquired many copies of these genes because they are located in a region of the genome that is difficult to sequence.

A recent study published in Science suggests that multiple copies of the gene may have been made in humans amylase — an enzyme that is the first step in the digestion of starch — over 800,000 years ago, long before the agricultural revolution. This genetic change may have helped us adapt to eating starchy foods.

The study shows how “what your ancestors ate thousands of years ago can influence our genetics today,” commented Dr. Kelsey Jorgensen, a biological anthropologist at the University of Kansas in Lawrence, Kansas, who was not involved in the study.

The double-edged sword has sharpened over the centuries. On the one hand, the human body needs and craves carbohydrates to function. On the other hand, our modern consumption of carbohydrates, especially high-calorie/nutritionally ineffective processed carbohydrates, has long since moved into the “healthy” category.

How scientists discovered our carb-lover gene

The enzyme amylase turns complex carbohydrates into maltose, a sweet-tasting sugar that consists of two glucose molecules joined together. We produce two types of amylase: salivary amylase, which breaks down carbohydrates in the mouth, and pancreatic amylase, which is secreted into the small intestine.

Modern humans have many copies of both amylases. Past tests showed that human populations eating a high-starch diet may have up to nine copies of the salivary amylase gene, called AMY1.

To determine when in human history we acquired multiple copies AMY1the new study used novel techniques called optical genome mapping and long-read sequencing to sequence and analyze genes. They sequenced 98 modern samples and 68 ancient DNA samples, including one from a Siberian who lived 45,000 years ago.

The ancient DNA data used in the study allowed scientists to track how the number of amylase genes changed over time, said Dr. George Perry, an anthropological geneticist at Pennsylvania State University-University Park (he was not involved in the study).

Based on the sequencing, the team analyzed changes in genes in the collected samples to assess the evolutionary time frame. Perry noted that this was “a very clever approach to estimating amylase copy number mutation rates, which in turn can really help test evolutionary hypotheses.”

Scientists have found that even before farming began, hunter-gatherers had between four and eight individuals AMY1 genes in their cells. This suggests that humans in Eurasia already had many of these genes long before cultivation began. (Last tests indicates that Neanderthals also ate starchy foods.)

“Even archaic hominins had these (genetic) differences, which indicates that they consumed starch,” said Dr. Feyza Yilmaz, a computational specialist at The Jackson Laboratory in Bar Harbor, Maine, and lead author of the study.

However, 4,000 years ago, after the agricultural revolution, research shows that there were even more of them AMY1 copies obtained. Yilmaz noted: “As agriculture progresses, we see an increase in high-copy amylase haplotypes. Thus, genetic variation goes hand in hand with adaptation to the environment.

AND previous study showed that species that live in the same environment as humans, such as dogs and pigs, also have variable numbers of copies of their amylase genes, Yilmaz said, pointing to a link between changes in the genome and increases in starch consumption.

Potential impact on the health of modern man

Duplicates in AMY1 the gene could have allowed people to digest starch better. You could imagine that having more copies of the gene means it can break down starch even more efficiently, and people with more copies “may be more susceptible to high blood sugar, prediabetes and the like,” Jorgensen said.

Regardless of whether they have more AMY1 genes carry greater health risks is an active area of ​​research. “Scientists checked whether there was a correlation between AMY1 gene copies and diabetes or BMI (body mass index). “So far, some studies show that there is indeed a correlation, but other studies show that there is no correlation at all,” Yilmaz said.

Yilmaz pointed out that only 5-10% of carbohydrates are digested in the mouth, the rest takes place in the small intestine, and many other factors influence eating and metabolism.

“I’m really looking forward to the research that really shows the connection between AMY1 copy number and metabolic health, as well as the types of factors that play a role in metabolic health,” Yilmaz said.

It is also possible that having more AMY1 copies may cause you to crave more carbohydrates because the enzyme produces a type of sugar in your mouth. “Previous research has shown that there is a correlation between AMY1 copy number, as well as the level of the amylase enzyme, so the faster we process the starch, the sweeter the (starch) taste will be,” Yilmaz said.

However, the relationship between cravings and copy number is not clear. And we don’t know exactly which came first – did the starch in the human diet lead to more copies of the amylase genes, or did the copies of the amylase genes trigger the appetite, which led us to grow more carbohydrates? We’ll need more research to find out.

How will today’s processed carbohydrates affect our genes tomorrow?

As our diet changes and includes more and more processed carbohydrates, what will happen to ours? AMY1 the genes are unclear. “I don’t know what impact this might have on our genomes over the next 1,000 or over 1,000 years,” Yilmaz noted, but based on the evidence, it appears we peaked in . AMY1 copies.

Jorgensen noted that this research focuses on the European population. He wonders if there is a pattern AMY1 replication will be repeated in other populations “as the increase in starch use occurred first in the Middle East, then in Europe, and later in the Americas,” she said.

“There is individual variation and also population variation,” Jorgensen noted. He speculates that the historical diets of different cultures may explain population differences AMY1 genes – this is something that future research may address. Other populations may also experience genetic changes as much of the world shifts to a higher-carbohydrate Western diet.

Overall, this study provides growing evidence that humans have a long history of loving carbohydrates – for better and, at least in our recent history and near future, for worse.