Paleo-diet debates evolve into something bigger

Paleo-diet debates evolve into something bigger
The article kicked off not just a diet but also a movement. Appearing in the New England Journal of Medicine in January 1985, “Paleolithic Nutrition: A Consideration of Its Nature and Current Implications” argued that the human body is “genetically programmed” to run not on a modern diet but on the foods consumed by our Stone Age ancestors.

“The human genetic constitution has changed relatively little since the appearance of truly modern human beings, Homo sapiens sapiens, about 40,000 years ago,” S. Boyd Eaton and Melvin Konner wrote.

The authors reasoned that human bodies have been shaped more by our prolonged time as hunter-gatherers than by the brief span since the advent of farming. Meat, probably lots of it, as well as fruits and vegetables were in. The staples of agriculture — breads, cereals, milks and cheeses — were not.

Three decades later, that academic ripple is now a popular tidal wave. We have not just Paleo diets — the subject of multiple bestsellers — but also Paleo exercise, Paleo sleeping and Paleo toilets. They’re all based on the premise that our bodies are more suited for Paleo-era habits.

But even as the “cave man” diet rose to become the most-Googled diet in 2013 and 2014, evolutionary biologists, with much less fanfare, were using advanced DNA techniques, sometimes on ancient bones, to suggest that Eaton and Konner’s premise may be off the mark: In fact, it seems, we have evolved.

Over the past year alone, prominent scientific journals have published evidence of genetic shifts in humans over the past 10,000 years — apparently in response to mankind’s transition to agriculture.

Two relatively recent gene variants help humans survive with deficiencies characteristic of agricultural diets; another genetic shift appears to help fight the dental cavities that arose with farm-based staples; another changes the way humans digest fats; dozens of others help fight the diseases that came with living at higher densities.

Those new findings add to previously known adaptations to mankind’s changing diet. After the domestication of milking animals, many humans evolved to digest milk. Humans also appear to have developed better ways to digest the starches characteristic of agricultural diets.

“It drives me crazy when Paleo-diet people say that we’ve stopped evolving — we haven’t,” said Anne C. Stone, a professor of human evolution at Arizona State University who has shown that genes related to starch digestion appear to have changed in number, apparently in response to farming. “Our diets have changed radically in the last 10,000 years, and, in response, we have changed, too.”

Although all this new evidence challenges the Paleo-diet argument, it doesn’t necessarily disprove it. And Eaton and Konner, for their part, maintain that their central hypothesis — that there is a mismatch between our bodies and our diets — remains sound.

Pace of research picks up
Yes, Konner said in an interview, there is more research that humans have evolved recently.

“There’s evidence that there’s been a lot more selection and genetic change in the last five to 10 thousand years than previously thought,” he said. “This is a challenge to the Paleo-diet claims — including mine and Boyd Eaton’s over the years.”

“But,” he said, “I don’t think it’s much of one.”

For one thing, he and Eaton say, the newly discovered genetic differences between Paleolithic hunter-gatherers and modern humans are not very numerous. Although there may be some ways in which humans have adapted to agricultural diets, those are far outnumbered by the ways in which human bodies remain suited for the Paleo era.

And even if one concedes that there has been significant genetic change over the past 10,000 years, Konner said, those changes would only catch us up to human diets from 10,000 years ago. But our diets have changed radically over the last 300 years alone — we consume less fiber, more refined grains, etc. — and evolutionary forces cannot have altered our bodies so quickly over that time.

“The bulk of the chronic degenerative disease in our population is due to dietary changes in the last few centuries; they’re not necessarily related to the shift from hunter-gatherers to agriculture,” Konner said. “The biggest culprit with the current epidemic of diabetes, a looming problem worldwide, is refined carbohydrates. There’s no way humans could have adapted to that because they haven’t been around long enough.”

The outcome of the debate rests for now on the ongoing research, which has accelerated markedly in recent years.

When Eaton and Konner wrote their article, the human genome had not been fully sequenced, and it was far more difficult to detect evidence of recent human evolution.

Take, for example, the discovery that humans gained the ability to digest milk — lactose tolerance — as they began to domesticate milking animals.

First, scientists had to discover that lactose tolerance is an inherited trait. This came about after scientists noticed similarities within families. Once that was established, scientists were forced to look for clues from geography and anthropology. What they found is that in populations where cattle had been long domesticated, most people could digest milk easily; in populations without domesticated milking animals, most could not.

“This trait seems to be common or extremely common only in populations which have established the custom of having milk regularly in their diet after weaning,” Stanford University geneticist Luigi Luca Cavalli-Sforza wrote in 1972. “It is rare or absent in others.”

Eaton and Konner acknowledged this dietary adaptation in their 1985 paper but said that “very few other examples are known.”

Signs of adaptation
After that, however, the pace of evolution research accelerated rapidly, especially with the ability to sequence the entire human genome. It allowed researchers, for example, to compare the DNA of populations with different diets — new and old — and look for signs of adaptation.

Stone and her colleagues, for instance, were interested in the varying abilities of people to handle diets loaded with starch. After the transition to agriculture, which brought steady supplies of wheat, corn, rice, barley and other crops, the ability to digest starches probably became more useful. Did human bodies adapt?

To answer that question, the researchers compared the DNA of peoples with high-starch diets and with the DNA of remote peoples who had low-starch diets.

The high-starch groups included European Americans, Japanese and Tanzania’s Hadza people, hunter-gatherers who rely on starch-rich roots. The low-starch groups were African pygmies, some African cattle farmers and a Russian ethnic group known as the Yakut.

DNA analysis showed that individuals from the high-starch groups were roughly twice as likely as the others to have inherited many extra copies of the AMY1 gene. The saliva of people with more copies of this gene tends to have more amylase, an enzyme that allows them to better digest starch.

More recently, another advance gave scientists a direct way of comparing contemporary humans to our Paleolithic ancestors by recovering DNA from ancient bones.

In a paper that appeared in December in the journal Nature, scientists looked at DNA recovered from the bones of more than 200 ancient Eurasian humans. The samples ranged from about 2,000 to 8,000 years old, a span that covers hunter-gatherers as well as early farmers.

The scientists noted thousands of distinct places in the DNA where there were changes that didn’t seem random but that instead appeared to be adaptation to environment.

From those thousands of places, the scientists highlighted 12 places where the signs of selection were clustered. One of those clusters related to the digestion of milk — a DNA change that confirmed previous findings. Another related to how humans digest fatty acids. Two others may have a link to celiac disease. Others were related to skin color, which got lighter as humans moved northward from Africa, and disease resistance.

“Europeans of 4,000 years ago were different in important respects from Europeans today, despite having overall similar ancestry,” the authors concluded.

Those findings, like the others, challenge the Paleo idea that humans have not changed. What remains unanswered, though, is how much change there has been.

“My overall opinion of this is that we don’t really know,” said Iain Mathieson, a Harvard University Medical School researcher and a co-author of the Nature paper. “We do know there are some specific changes in humans. But they are relatively small in number. To me, it’s an open question. It’s a hypothesis.