Trying to reduce your carbohydrate intake means going against nearly a million years of evolution.
Humans are among a few species with multiple copies of certain genes that help us break down starch — carbs like potatoes, beans, corn, and grains — so that we can turn it into energy our bodies can use.
However, it’s been difficult for researchers to pinpoint when in human history we acquired multiple copies of these genes because they’re in a region of the genome that’s hard to sequence.
A recent study published in Science suggests that humans may have developed multiple copies of the gene for amylase — an enzyme that’s the first step in starch digestion — over 800,000 years ago, long before the agricultural revolution. This genetic change could have helped us adapt to eating starchy foods.
The study shows how “what your ancestors ate thousands of years ago could be affecting our genetics today,” said Kelsey Jorgensen, PhD, a biological anthropologist at The University of Kansas, Lawrence, who was not involved in the study.
The double-edged sword has sharpened over all those centuries. On one hand, the human body needs and craves carbs to function. On the other hand, our modern-day consumption of carbs, especially calorie-dense/nutritionally-barren processed carbs, has long since passed “healthy.”
How Researchers Found Our Carb-Lover Gene
The enzyme amylase turns complex carbs into maltose, a sweet-tasting sugar that is made of two glucose molecules linked together. We make two kinds of amylases: Salivary amylase that breaks down carbs in our mouths and pancreatic amylase that is secreted into our small intestines.
Modern humans have multiple copies of both amylases. Past research showed that human populations with diets high in starch can have up to nine copies of the gene for salivary amylase, called AMY1.
To pinpoint when in human history we acquired multiple copies of AMY1, the new study utilized novel techniques, called optical genome mapping and long-read sequencing, to sequence and analyze the genes. They sequenced 98 modern-day samples and 68 ancient DNA samples, including one from a Siberian person who lived 45,000 years ago.
The ancient DNA data in the study allowed the researchers to track how the number of amylase genes changed over time, said George Perry, PhD, an anthropological geneticist at The Pennsylvania State University-University Park (he was not involved in the study).
Based on the sequencing, the team analyzed changes in the genes in their samples to gauge evolutionary timelines. Perry noted that this was a “very clever approach to estimating the amylase copy number mutation rate, which in turn can really help in testing evolutionary hypotheses.”
The researchers found that even before farming, hunter-gatherers had between four and eight AMY1 genes in their cells. This suggests that people across Eurasia already had a number of these genes long before they started growing crops. (Recent research indicates that Neanderthals also ate starchy foods.)
“Even archaic hominins had these [genetic] variations and that indicates that they were consuming starch,” said Feyza Yilmaz, PhD, an associate computational scientist at The Jackson Laboratory in Bar Harbor, Maine, and a lead author of the study.
However, 4000 years ago, after the agricultural revolution, the research indicates that there were even more AMY1 copies acquired. Yilmaz noted, “with the advance of agriculture, we see an increase in high amylase copy number haplotypes. So genetic variation goes hand in hand with adaptation to the environment.”
A previous study showed that species that share an environment with humans, such as dogs and pigs, also have copy number variation of amylase genes, said Yilmaz, indicating a link between genome changes and an increase in starch consumption.