Low-protein diet: How orangutans survive
RUTGERS (US) — How orangutans survive during extreme food shortages may help scientists better understand human eating disorders and obesity.
“There is such a large obesity epidemic today and yet we don’t really understand the basis of the obesity condition or how these high-protein or low-protein diets work,” says Erin Vogel, an evolutionary anthropologist at Rutgers.
Vogel’s work with endangered Indonesian orangutans—considered a close relative to humans—represents the first time scientists have looked at how these long-haired, orange-colored apes endure protein cycling, or period bouts of protein deprivation.
“I think studying the diets of some of our closest living relatives, the great apes; may help us understand issues with our own modern day diets,” she says.
The study, reported in the journal Biology Letters, shows that it’s only during periods of high caloric and protein intake that orangutans put on fat, a scientific fact that is sometimes ignored by those who believe that high protein, low carbohydrate diets are the best way to lose weight.
Vogel says it is only when caloric intake is restricted that orangutans use these fat reserves for energy and eventually dip into their protein (muscle) reserves—a condition that is seen with eating disorders like anorexia.
Orangutans in particular are interesting to study, Vogel says, because they are the only documented species of non-human ape to store fat when food is abundant in the wild and use these fat reserves when preferred fruits become scarce, presumably something done by our early hominin ancestors.
Vogel and her research team analyzed samples collected over a five-year period to study the effects of protein recycling, which included examining urinary metabolites and nitrogen stable isotopes—compounds and byproducts in orangutan urine.
What they determined is that these primates are able to endure prolonged protein deficits without starving to death by consuming higher protein leaves and inner bark and obtaining energy from their stored body fat and even muscles for an extended period of time when low-protein fruit is unavailable.
“We discovered through this research that the daily amount of protein the orangutans take in when fruit is not available is inadequate for humans and one-tenth of the intake of mountain gorillas. But it is sufficient to avert a severe protein deficit,” says Vogel.
The Bornean orangutan population has fallen drastically in the last 50 years in Indonesia to less than 55,000 and on the island of Sumatra to less than 5,000 due to a massive amount of illegal logging and further clearing of the land to develop palm oil plantations in their now impoverished rainforest habitat.
Vogel says that although some palm oil companies argue that clearing partially logged areas of the rainforest for palm oil plantations is not detrimental to the existence of the orangutan because their natural habitat has already been taken away, this research on protein cycling indicates that even areas that have been partially stripped of trees are better for orangutan survival than no forest area at all.
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