Humans were born to be the ‘fat primates,’ scientists say

It’s a discovery so frustrating you might want to hit the couch and down a pint of ice cream.

“We’re the fat primates,” says Devi Swain-Lenz, a postdoctoral associate in biology at Duke University. She and her team have discovered one reason why humans are so much heavier than our monkey relatives. Their findings appear in the latest issue of Genome Biology and Evolution.

To put this in perspective, even the fittest humans can have twice the amount of body fat as a typical chimp, which is usually less than 9 percent. A healthy human body fat percentage can be anywhere from 14 to 31 percent.

Even though chimps and humans have nearly identical DNA sequences, there’s a critical difference in how our DNA is packed in fat cells. This difference has led humans to lose their ability to efficiently turn “bad” fat into the “good” calorie-burning kind.

Swain-Lenz explains there are two types of fat in play here: white and brown. White fat — the stuff that gives steak marbling or hangs on our hips — stores calories. On the other hand, cells called beige or brown fat actually burns calories for energy.

For the study, Swain-Lenz and her colleagues sampled fat from humans, chimps and an even more distantly related species, the rhesus macaques, analyzing the differences in their genomes to reveal how DNA functions within fat cells.

DNA is usually so tightly woven around protein within cells that only certain parts of the strand can be activated. In chimps and macaques, researchers found around 780 DNA regions that, for humans, have become inaccessible. Within these regions were genes designed to convert white fat into brown.

“We’ve lost some of the ability to shunt fat cells toward beige or brown fat, and we’re stuck down the white fat pathway,” says Swain-Lenz.

Scientists suggest the reason for our white fat buildup had something to do with our evolutionary needs — possibly to feed our large brains, which have tripled in size since we departed from our chimp cousins. Their brains, however, are no bigger millions of years later.

Swain-Lenz says it is possible to put our body’s limited store of brown fat to use, “but we need to work [harder] for it.” Knowing how to turn white fat into beige or brown, scientists believe, might be the key to helping us slim down — and would probably make Swain-Lenz and her colleagues very rich.

“I wish,” she says.

Unfortunately, that won’t be happening anytime soon.

“Maybe we could figure out a group of genes that we need to turn on or off, but we’re still very far from that,” says Swain-Lenz. “I don’t think that it’s as simple as flipping a switch. If it were, we would have figured this out a long time ago.”

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