What made humans 'the fat primate'?

fat person
Credit: CC0 Public Domain

Blame junk food or a lack of exercise. But long before the modern obesity epidemic, evolution made us fat too.

"We're the fat primates," said Devi Swain-Lenz, a postdoctoral associate in biology at Duke University.

The fact that humans are chubbier than chimpanzees isn't news to scientists. But new evidence could help explain how we got that way.

Despite having nearly identical DNA sequences, chimps and underwent critical shifts in how DNA is packaged inside their , Swain-Lenz and her Duke colleagues have found. As a result, the researchers say, this decreased the 's ability to turn "bad" calorie-storing fat into the "good" calorie-burning kind.

The results were published June 24 in the journal Genome Biology and Evolution.

Compared to our closest animal relatives, even people with six-pack abs and rippling arms have considerable fat reserves, researchers say. While other primates have less than 9% , a healthy range for humans is anywhere from 14% to 31%.

To understand how humans became the fat primate, a team led by Swain-Lenz and Duke biologist Greg Wray compared fat samples from humans, chimps and a more distantly-related monkey species, rhesus macaques. Using a technique called ATAC-seq, they scanned each species' genome for differences in how their fat cell DNA is packaged.

Normally most of the DNA within a cell is condensed into coils and loops and tightly wound around proteins, such that only certain DNA regions are loosely packed enough to be accessible to the cellular machinery that turns genes on and off.

The researchers identified roughly 780 DNA regions that were accessible in chimps and macaques, but had become more bunched up in humans. Examining these regions in detail, the team also noticed a recurring snippet of DNA that helps convert fat from one cell type to another.

Not all fat is created equal, Swain-Lenz explained. Most fat is made up of calorie-storing white fat. It's what makes up the marbling in a steak and builds up around our waistlines. Specialized fat called beige and brown fat, on the other hand, can burn calories rather than store them to generate heat and keep us warm.

One of the reasons we're so fat, the research suggests, is because the regions of the genome that help turn white fat to brown were essentially locked up—tucked away and closed for business—in humans but not in chimps.

"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," Swain-Lenz said. It's still possible to activate the body's limited brown fat by doing things like exposing people to cold temperatures, she explained, "but we need to work for it."

Humans, like chimps, need fat to cushion vital organs, insulate us from the cold, and buffer us from starvation. But early humans may have needed to plump up for another reason, the researchers say—as an additional source of energy to fuel our growing, hungry brains.

In the six to eight million years since humans and chimps went their separate ways, brains have roughly tripled in size. Chimpanzee brains haven't budged.

The human brain uses more energy, pound for pound, than any other tissue. Steering fat cells toward calorie-storing white fat rather than calorie-burning brown fat, the thinking goes, would have given our ancestors a survival advantage.

Swain-Lenz said another question she gets a lot is: "Are you going to make me skinny?"

"I wish," she said.

Because of brown fat's calorie-burning abilities, numerous researchers are trying to figure out if boosting our body's ability to convert to beige or could make it easier to slim down.

Swain-Lenz says the differences they found among primates might one day be used to help patients with obesity—but we're not there yet.

"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," Swain-Lenz said. "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," she explained.

Explore further

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More information: Devjanee Swain-Lenz et al, Comparative analyses of chromatin landscape in white adipose tissue suggest humans may have less beigeing potential than other primates, Genome Biology and Evolution (2019). DOI: 10.1093/gbe/evz134
Provided by Duke University
Citation: What made humans 'the fat primate'? (2019, June 26) retrieved 18 July 2019 from https://phys.org/news/2019-06-humans-fat-primate.html
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Jun 26, 2019
Orangutan males store large fat deposits

Jun 26, 2019
Orangutan males store large fat deposits

Yeah, but they don't have easy access to McDonald's.

Jun 26, 2019
Or, as @Benni might say: "Because of the invention of 'exotic' Dark Matter which increased their mass to five times. "

ps @Benni. Sorry if I co-opted/pre-empted/re-purposed this usual 'long patented' exotic-DM-related 'sarcastic standby' of yours, mate. Couldn't resist. :)

Jun 26, 2019
This is another junk article. Evolution did not make anyone fat. It still doesn't today. Our own lust does. Quick trying to put the blame on anything else.

Jun 27, 2019
As we have diverged from our chimp cousins, most of us have also become less hairy. That leaves 2 ways to maintain heat. Either burn more calories (brown fat) which means higher food requirement and therefore more starvation risk in lean times, or use subcutaneous white fat as passive insulation (and not require extra food intake). Sure, of course an enlarged working brain needs more calories, but that is not necessarily the only reason for the change to white fat.
Sexual selection may have also played a role.

Jun 27, 2019
Beautiful paper, thanks. It explains how we became so fat.
*Why* we became so fat is well-known - it also explains why we became so brainy:

Archaic Homo (probably in the early Ice Ages, cf lowering sea-levels) dispersed intercontinentally following African & Eurasian coasts (cf early-Pleistocene H.erectus fossils in deltaic sediments, e.g. Mojokerto etc.), where they frequently dived for shellfish etc.: seafood=brainfood.
IOW, we evolved thick subcutaneous white fat like all other medium-sized or larger littoral mammals, google e.g.
"coastal dispersal of Pleistocene Homo 2018 biology vs anthropocentrism".

Jun 28, 2019
It's not a "blog." It's a science news aggregation site. And this is the comments section.

Ivan. Or Wang. Whatever.

Jun 29, 2019
IOW, we evolved thick subcutaneous white fat like all other medium-sized or larger littoral mammals, google e.g. "coastal dispersal of Pleistocene Homo 2018 biology vs anthropocentrism".

Don't google that, unless the "littoral mammal" reference to the rejected fringe "aquatic ape theory" wasn't a tip off. Obviously humans, or any other monkey, aren't sea living mammals.

Verhaegen is a prominent peddler of that nonsense by the way - google that fact instead.

Jun 29, 2019
Gluten sensitivity

This gluten sensitivity that is spreading this globe
For if you ever become sensitive to gluten
You will wish you hadn't
For you cannot digest as it is celiac disease
For these cilia shrivel and die for the body reacts to wheat barley and rye
As this is why everyone is getting fat
Because from bread to muffins pancakes soup cornflakes
In fact almost everything has wheat barley and rye
From booze to malt vinegar on chips to bread crumbs on these fish in these fish n chips
For when you simply cut out wheat barley and rye
Your health recovers
You are no longer bloated
Your waist line drops
As does your weight
Because as you pass the bread and cake counter by
The canned soup counter cereal counters by
As all these contain wheat barley and rye
But fortunately it is safe to eat
Black syrup for it is high in iron
Milk and dark chocolate also high in iron, gluten free bread,
So there are advantages in becoming gluten sensitive
It does wonders for your waist line

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