Like humans, dolphins burn calories at lower rate as they get older

New York: Humans aren't the only species whose metabolisms tend to slow down with age.

A Duke University-led study finds that bottlenose dolphins burn calories at a lower rate as they get older, just like we do.

It is the first time scientists have measured an age-related metabolic slowdown in another large-bodied species besides humans, said Rebecca Rimbach, postdoctoral associate in evolutionary anthropology at Duke.

The findings could shed light on factors besides diet and lifestyle that underlie age-related weight gain in people.

Despite living in a watery world, the team found that bottlenose dolphins burn 17 per cent less energy per day than expected for a marine mammal of their size.

The scientists also noted some of the same signs of metabolic ageing common in people. The oldest dolphins in the study, both in their 40s, used 22 per cent to 49 per cent fewer calories each day than expected for their body weight.

And similar to humans, more of those calories ended up as fat rather than muscle. Dolphins in their 40s had body fat percentages that were 2.5 times higher than their under-20 counterparts.

The researchers studied 10 bottlenose dolphins aged 10 to 45 living at two marine mammal facilities, Dolphin Research Center in Florida and Dolphin Quest in Hawaii.

To measure their average daily metabolic rate, the team used the "doubly labelled water method." Used to measure energy expenditure in humans since the 1980s, it is a method that involves getting the animals to drink a few ounces of water with naturally occurring "heavy" forms of hydrogen and oxygen added, and then tracking how long the animals take to flush them out.

Like humans presenting their arms for a blood draw, the dolphins at these facilities voluntarily raise their tail fins out of the water so their caregivers can collect blood or urine as part of their regular checkups.

By analysing the levels of heavy hydrogen and oxygen atoms in the blood or urine, the team was able to calculate how much carbon dioxide the dolphins produced each day, and thus how many calories they were burning as they went about their lives.