Obesity isn’t just a human scourge – it can also impact animal health. And looking at elephants, you could be excused for thinking they need to go on a diet. But researchers have found that, on the whole, they have less body fat than the average person.
“We know that in other species, excess adiposity is related to different morbidities,” says Daniella Chusyd from the University of Alabama, US, lead author of a study published in the Journal of Experimental Biology.
In mammals such as dogs, horses and non-human primates, for instance, Chusyd and co-authors note that obesity has been linked to risk of diabetes.
In elephants, studies have reported that those in captivity carry more fat than their wild counterparts, leading to concerns about obesity. But to measure their excess fat, most had used a body condition score that basically relies on observation.
“We wanted to quantify body composition, for the first time, rather than rely on a visual assessment of external fat cover,” says Chusyd, “to provide a better understanding of how actual fatness is related to physiological function in the Asian elephant.”
This is important, according to the authors, because Asian elephants (Elephas maximus) are endangered, and while captive breeding is one way of protecting them, many populations face health and reproductive problems that could be related to excess fat.
The team, which includes researchers from the Smithsonian Institute, China and the UK, used “heavy water” to estimate fat levels of 44 North American zoo elephants (35 female), and investigated how this related to the animals’ metabolic health and activity levels. They also explored links between body fat and reproductive status of the female elephants.
Heavy water (deuterium oxide) is a gold standard method to estimate body composition by measuring total body water and subtracting from body mass to calculate fat levels.
It would be tricky to give to elephants without spillage, though. To get around this, the researchers poured it on bread so the elephants could eat it. “I quickly became their best friend,” says Chusyd.
Multiple blood samples were collected before and after the happy study participants ate their bread, to track the heavy water in their bodies and measure different health biomarkers including glucose, insulin and female hormone levels.
As many human research volunteers have experienced, the team even used accelerometers (elephant-sized), attached to the animals’ legs, to measure how many steps they took and converted them into total distance based on stride length.
Results showed that, on average, the males carried slightly less fat relative to body mass (around 8.5%) than females (around 10%). This is comparable to average fat levels of 6–31% in healthy humans. Overall, body fat ranged from 2% to 25%. For comparison, the average American woman and man carry around 40% and 28% body fat, respectively.
Surprisingly, the infertile females had less body fat, comparable to the disrupted fertility cycles of underweight human females. And happily, the team found that their study population walked similar distances to free-ranging animals.
But the elephants’ body fat was correlated with insulin levels, suggesting those with more fat could have metabolic problems. The authors say more work is needed to determine what an unhealthy amount of fat is for elephants.
“It appears it is possible that with continued fat accrual, an elephant can develop a diabetic-like state,” says Chusyd. “It may also be possible that voluntary walking is enough to reduce the amount of relative fat the elephant has.”