Study on orangutans in Borneo to shed light on human

CHICAGO (Reuters) - 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 behavior 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, U.S.
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.
[You must be registered and logged in to see this image.] An
orangutan is pictured after being released into the forest at Seruyan,
of Tanjung Puting National Park, central Kalimantan November 21, 2011. -
REUTERS
"Orangutans living in this really challenging
habitat are able to take advantage of these periods of incredible fruit
abundance -- these masting periods, where 80 percent of the fruit on the
trees are fruiting," Vogel said.
"They eat and eat and eat and they get fat," she said.
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 metabolizing 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.
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
signaling 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.