Orangutan snack binges give insight into human obesity

In lush times, orangutans on the island of Borneo gorge themselves on forest fruits, packing on extra pounds in preparation for leaner years, when they live off leaves and bark and their own stored fat.

This behaviour of overeating is all too common in humans, but rarely seen in nonhuman primates, and studying it may offer some clues about obesity and eating disorders in people, US researchers said on Tuesday.

“Orangutans make very interesting models for studying human obesity because they are really the only apes and potentially the only nonhuman primates in the wild that actually store fat deposits,” said Erin Vogel, an evolutionary anthropologist from Rutgers University in New Jersey, whose study appears in the journal Biology Letters.

“It’s never been documented in any other species,” Vogel said in a telephone interview.

Vogel and colleagues studied urine samples from Bornean orangutans laboriously collected over a period of five years by a team led Dr Cheryl Knott, a biological anthropologist at Boston University.

“Orangutans living in this really challenging habitat are able to take advantage of these periods of incredible fruit abundance — these masting periods, where 80% of the fruit on the trees are fruiting,” Vogel said.

“They eat and eat and eat and they get fat,” she said.

Burning fat
Then they go through periods of very low fruit production that can last up to eight years.

In the study, as food stores became more and more scarce, the orangutans shifted to bark and tough leaves to survive. And the team noticed changes in the apes’ urine.

First, they saw ketones, a sign that the body was metabolising fat. “It indicates they are burning this fat for energy,” Vogel said.

And then they saw elevated nitrogen isotopes. These indicated that muscle cells were being broken down to obtain protein and energy.

“They have to get energy from somewhere, so they start to digest their body tissue, just like you would find in situations were humans are very impoverished, and in anorexia, where we would potentially see conditions where humans would digest their own muscles,” Vogel said.

Vogel credits Knott’s team for collecting the urine samples, which was no mean feat.

The team followed the orangutans from the time they woke up in their nest until the time they went to sleep.

“As soon as they wake up, they typically void — they urinate,” Vogel said.

A wonderful ability
Knott’s team would be waiting underneath the tree canopy to collect these samples, either with plastic sheeting or an inverted umbrella held over their heads, which worked as both a collection device and some protection from the shower of urine.

Vogel said the study shows how orangutans have taken advantage of their ability to store fat to increase their chances of survival, but this same ability is a deficit for most humans who do not need to forage for food.

“We have this wonderful ability to store fat, and now most of us wish we didn’t have it,” she said.

In future studies, Vogel said she plans to look for fluctuations in the hunger-related hormones ghrelin and leptin during periods of food scarcity and abundance, as well as changes in inflammatory cell signalling chemicals known as cytokines, which are thought to play a role in obesity.

Orangutans are endangered. There are only 50 000 individuals remaining in Borneo and 7 300 in Sumatra — the two places in the world where they can still be found in the wild. — Reuters

Subscribe to the M&G

These are unprecedented times, and the role of media to tell and record the story of South Africa as it develops is more important than ever.

The Mail & Guardian is a proud news publisher with roots stretching back 35 years, and we’ve survived right from day one thanks to the support of readers who value fiercely independent journalism that is beholden to no-one. To help us continue for another 35 future years with the same proud values, please consider taking out a subscription.

Related stories

Catholic NGO boss accused of racism and abuse in Sudan

The aid worker allegedly called his security guard a ‘slave’

Fake trafficking news targets migrants

Exaggerated reports on social media of human trafficking syndicates snatching people in broad daylight legitimate xenophobia while deflecting from the real problems in society

How US foreign policy under Donald Trump has affected Africa

Lesotho has been used as a microcosm in this article to reflect how the foreign policy has affected Africa

The challenges of delivering a Covid-19 vaccine in Africa requires a new approach

It is imperative that we train healthcare workers and participate in continent-wide collaboration

Spain detains software creator McAfee wanted in US

The announcement of his arrest comes a day after US prosecutors released an indictment against McAfee for allegedly failing to report income

Richard Calland: South Africa needs a Roosevelt style of leadership

President Cyril Ramaphosa needs to hold ‘fireside chats’ and have more power and institutional muscle around him, writes Richard Calland

Subscribers only

Toxic power struggle hits public works

With infighting and allegations of corruption and poor planning, the department’s top management looks like a scene from ‘Survivor’

Free State branches gun for Ace

Parts of the provincial ANC will target their former premier, Magashule, and the Free State PEC in a rolling mass action campaign

More top stories

Vitamin therapy is for drips

It may be marketed by influencers, but intravenous vitamin therapy is not necessary and probably not worth the hype, experts say

Facebook, Instagram indiscriminately flag #EndSars posts as fake news

Fact-checking is appropriate but the platforms’ scattershot approach has resulted in genuine information and messages about Nigerians’ protest against police brutality being silenced

Murder of anti-mining activist emboldens KZN community

Mam’Ntshangase was described as a fierce critic of mining and ambassador for land rights.

Unite with Nigeria’s ‘Speak Up’ generation protesting against police brutality

Photos of citizens draped in the bloodied flag have spread around the world in the month the country should be celebrating 60 years of independence

press releases

Loading latest Press Releases…

The best local and international journalism

handpicked and in your inbox every weekday