The metabolism of humans peaks during their younger years and slowly declines as they get older, no matter how much they exercise. Now, experts from Duke University have shown that, like people, bottlenose dolphins burn calories at a lesser rate as they grow old.
The study titled "Total Energy Expenditure of Bottlenose Dolphins (Tursiops truncatus) of Different Ages," published in the Journal of Experimental Biology, is the first study to measure an age-related metabolic slowdown in another species aside from humans.
Studying Energy Expenditure in Dolphins
According to Phys.org, study first author Rebecca Rimbach, a postdoctoral associate in Duke, is studying energy expenditure in animals. However, data about energy expenditure in whales, dolphins, and other marine mammals are scant because they are difficult to recapture for repeat measurements.
In the study, the researchers measured the daily metabolic rate of 10-45 bottlenose dolphins from Dolphin Research Center in Florida and Dolphin Quest in Hawaii. They used the "doubly labeled water method" to measure the energy expenditure of dolphins. This method was also used in humans for the same purpose since the 1980s.
The method involves getting mammals to drink a few ounces of water that contains natural heavy forms of hydrogen and oxygen atoms. Then, they track down how long dolphins were able to flush them out. This will help them calculate the amount of carbon dioxide dolphins produce every day, which equates to dolphins' metabolism rate.
Like humans who voluntarily preset their arms for scientists to draw blood, dolphins also voluntarily raise their tail fins out of the water so their caregivers can collect their blood and urine during their regular check-ups.
Dolphins Show the Same Metabolic Aging Like Humans
Duke University's news release reported that researchers were amazed to find that dolphins burn 17% less energy everyday than what they expected from a warm-blooded mammal of such size. Scientists noted that dolphins showed similar signs of metabolic aging like humans, wherein the oldest dolphins that are in their 40s used 22% to 49% fewer calories per day than what is expected for their body weight.
More so, their unburned calories turn to fat rather than muscles, much like what happens in humans. The team said that dolphins in their 40s have body fat 2.5 times higher than their counterparts under 20s.
They emphasized that this was neither due to lack of exercise nor excessive eating. The dolphins in the study can do flips and spins, walk on their tails, and swim alongside powerboats. However, their metabolic pattern remained no matter what level of physical activity they do.
Researchers said that they need more data to see how the study could help in understanding metabolism in humans. They especially need to study the metabolism rate in younger dolphins.
In humans, as Medical Xpress reported, metabolism peaks during infancy and gradually declines through childhood and teenage years. By the time they reach adulthood, they maintain a surprisingly consistent level of metabolism until they reach their senior years.
Researchers from Duke hope to conduct further studies on the commonality between dolphins and humans to help further understand the metabolic aging process in humans, according to the news release.
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