NKRIKU, Jakarta – A study led by Duke University, United States, found that bottlenose dolphins burn calories at a lower rate as they age. This means that the mammal will feel that its metabolism is not like it used to be, just like humans.
To measure their average daily metabolic rate, the researchers used the “double-labeled water method.” Used to measure energy expenditure in humans since the 1980s, this method involves animals drinking a few ounces of water in the form of naturally added “heavy” hydrogen and oxygen, then tracking how long it takes the animal to excrete it.
Like humans showing their hands to draw blood, the dolphins at this facility voluntarily lift their tail fins out of the water. So their caregivers can collect blood or urine as part of their routine checkups.
By analyzing 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 produce each day. “And thus knowing how many calories they burn as they go about their lives,” the study wrote.
The researchers expected the dolphins to have increased metabolisms, because dolphins are warm-blooded just like humans, and staying warm requires more energy in the water than in the air. But despite living in a watery world, they found that bottlenose dolphins burn 17 percent less energy per day than expected for a marine mammal of their size.
The scientists also noted some of the same signs of metabolic aging that are common in humans. The oldest dolphins in the study, both in their 40s, used 22-49 percent fewer calories each day than expected for their body weight.
And similar to humans, more calories end up as fat than muscle. Dolphins in their 40s have a body fat percentage 2.5 times higher than dolphins under 20.
“Not for lack of exercise. Dolphins are extraordinary athletes, able to jump 10 feet into the air and swim in fast electric boats,” said Rimbach.
The dolphins in this study were observed to perform flipping and spinning movements, walking on their tails, jumping out of the water and moving fast enough to get up six to 18 times in an hour. And they remain active until their 40s.
However, the metabolic pattern remains unconcerned with their activity level. According to Rimbach, it’s not because they eat too much. The researchers recorded how much fish the dolphins ate, and they found that the older, fatter dolphins in the study actually ate fewer calories.
“We need more data, especially for the younger dolphins, because we only looked at 10 individuals,” Rimbach said, “while adding, “but I think it’s an interesting first study.”
Researchers say such work could explain factors other than diet and lifestyle that underlie age-related weight gain in people. Rimbach’s colleague, who was also involved in the study, Hannah Salomons, said further studies of the similarities between humans and dolphins could help understand why human metabolism slows down with age.
“Having access to healthy dolphins under human care made this research possible,” said co-author Austin Allen of the Duke University Marine Lab.
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