Jan. 26 (UPI) -- The obesity crisis thought to be plaguing Asian elephants was a mirage, according to a new study published in the Journal of Experimental Biology.
After a number of scientists began publishing data suggesting large numbers of captive Asian elephants were overweight, researcher Daniella Chusyd noted that obesity might explain the fertility crisis facing captive elephants.
In humans, a declining birth rate is one of several health problems linked with obesity. Chusyd estimated an obesity epidemic might engender similar health problems in captive elephants.
The problem was, Chusyd realized, no one had set out to define obesity in Asian elephants.
To make comparisons between the problem of obesity in humans and elephants, he needed to know how much fat a healthy captive elephant typically carries.
"I was interested in discovering whether methods predominantly used in human health research could help us learn more about elephants," Chusyd, who began the research while working at University of Alabama at Birmingham, said in a news release. "Obesity is not clearly defined in humans, let alone elephants."
For the study, researchers used heavy water to measure the body water content of several dozen captive elephants at zoos across the United States and Canada.
By calculating how much water an elephant carried, scientists were able to determine the elephant's total body fat.
Heavy water is water featuring molecules containing deuterium atoms. Deuterium is a stable isotope of hydrogen with a mass roughly twice that of the normal isotope.
"We came up with the idea of using bread soaked with heavy water to deliver it to the elephants," said Chusyd, who now works as postdoctoral research fellow at Indiana University.
The elephants were quite fond of the treat.
"I quickly became their best friend," Chusyd said.
Scientists collected blood samples before and up to 20 days after feeding the elephants heavy water to track the distribution of deuterium water in their bodies.
Using the water content totals, researchers estimated the fat content of male and female elephants.
On average, male elephants carried 8.5 percent body fat, while females carried an average of 10 percent body fat.
The body fat content of females ranged from 2 to 25 percent, though males are larger and carried more total fat. The body fat content carried by health humans ranges between 6 and 31 percent.
To better understand the relationship between fat content and elephant health, researchers fit the same captive Asian elephants with fitness trackers.
The data showed all of the captive elephants walked distances comparable to free-ranging elephants each day.
Researchers also found the elephants with the lowest fertility rates were those carrying the least body fat -- fertility problems can also present in underweight female humans, scientists noted.
Blood tests showed that insulin levels in the elephants with the most body fat were elevated.
While the average elephant isn't as fat as the average human, research suggests it's still possible that excess fat could cause health problems for some elephants.
"It is possible that elephants could develop a diabetic-like state," said Chusyd.
Even if elephants could, in theory, experience obesity, Chusyd and her colleagues are confident that captive Asian elephants in North America aren't suffering an obesity epidemic.
"They are doing a great job ... they know their individual elephants best," she said of the animal caretakers.