Updated August 17, 2024 at 07:11 AM ET
Some bats like candy.
Well, not the kind of candy you buy in a sweets shop. Rather, they like fruit, which is rich in sugar.
“We call it nature’s candy,” says Wei Gordon, a biologist at Menlo College. She was catching neotropical bats this spring in northern Belize as part of the Bat-a-thon, an annual event when dozens of researchers converge to study many kinds of neotropical bats — including fruit bats, the subset that feast on fruit.
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Gordon wonders whether these furry, flying enigmas might hold clues to treating diabetes in people. That’s because when fruit bats gorge on fruit, it jacks their blood sugar. But somehow, it doesn’t cause them any harm.
“These bats control sugar like it was nothing,” says Nadav Ahituv, who is standing near Gordon. He’s the director of the Institute for Human Genetics at the University of California San Francisco. Ahituv likes to think of bats as little superheroes — each with their own special superpower. For the fruit bats, their superpower is their capacity to handle so much sugar.
This isn’t the case for humans: We have to be careful about how much sugar we consume. That’s because “diets rich in sugar contribute to things like diabetes,” says Gordon. “And it’s just gonna cause a lot of havoc.”
Gordon says fruit bats may keep enough sugar circulating in their blood to power their flight to their next fruit meal. “They are really dependent on having sugar ready to go in their system to fuel their lifestyle,” she says. Within half an hour of a fruit feast, though, the bat can pretty much bring its sugar levels back to where they started.
“So the question is,” Gordon asks, “how do they bring [their blood sugar] down so low, so quickly? How can they handle it without acquiring some sort of metabolic disease?”
Fruit bats are wired differently
A lot of the sugar that we consume winds up in our blood as glucose. Insulin helps us manage that glucose and get it to the cells that need it. But over the last two decades, a combination of factors, including a decrease in exercise and changes in our diets, have caused diabetes to surge worldwide. The disease is characterized by an inability to regulate blood sugar, which can lead to heart disease, nerve damage, blindness and in some cases, death.
To learn more about how fruit bats manage their sugar, Gordon set out to compare fruit bats to bats that eat insects, a diet that’s rich in protein but low in sugar.
Along with Ahituv and other colleagues, she was particularly interested in the kidney and pancreas, organs that researchers already knew looked different to the naked eye between the two kinds of bats.
So Gordon zoomed in on them to compare the cells and genes of those organs. “And what was really exciting is that in fruit bats,” she says, “we did see a lot more cells that are responsible for maintaining your blood sugar.” That is, they had more pancreas cells available to produce insulin compared to the insect-eaters.
Plus, the fruit bats had genetic differences that seemed to allow them to act quickly to control the blood sugar coursing through their bloodstream. “The genes were sort of primed” to pump out insulin, for example, as soon as it was needed, says Gordon.
The results were published early this year in the journal Nature Communications. Gordon says that one day, such features of fruit bats might teach us how to help people regulate their sugar levels.
“Yes, very much down the road,” Gordon says, “but that would be the ultimate, ‘Wow, we did it.’”
The fuzzy Olympians of sugar consumption
When it comes to bats, there are superheroes … and then there are SUPERHEROES.
Take Glossophaga mutica — a kind of nectar feeding bat the color of milk chocolate that’s found in the Americas.
“These are basically hummingbirds of the night, drinking floral nectar,” says Jasmin Camacho, an evolutionary biologist at the Stowers Institute for Medical Research in Missouri. “Evolution has shaped them to go around and enjoy all the sweets.”
Camacho, who’s in Belize with the Bat-a-thon as well, stands inside a big screened walk-in tent at 2 a.m. one night. She’s holding a Glossophaga mutica bat that was caught earlier in the evening. She feeds the bat a little sugar water and he licks it right up. This is just a drop in the bucket for this guy. Nectar feeders consume even more sugar than fruit eaters.
“Their biology is so extreme,” she says. “They’ll go around foraging up to 800 flowers a night. So that’s basically like every night, they’re eating their body weight in sugar. Imagine eating your body weight in sugar every day.”
For humans, that would be a one-way ticket to metabolic catastrophe — diabetes, obesity or worse.
“That is industrial levels,” says Camacho. “That is toxic. That is gonna kill you.” But nectar bats “go beyond what we know is survivable for other types of mammals,” she say — and somehow don’t get sick. Unlike the fruit bats that can “rapidly lower their blood glucose with insulin,” she says, “nectar bats keep their blood sugar levels higher for longer periods of time.”
Camacho wants to know how the nectar feeders manage that much glucose without health problems. She thinks the answer may lie, at least in part, in all the flying the bats do. Just think of a nectar-feeding bat flapping its wings at least twelve times a second, darting from flower to flower and slurping up glucose and other sugars all night long. That’s a lot of cardio.
“When you exercise,” says Camacho, “you’re able to uptake about 100 times more glucose than you would with insulin.” That is — ”when we exercise, we use more energy.”
So maybe these bats don’t absorb all the sugar to store it away in their bodies. Rather, similar to fruit bats, they keep it circulating in their bloodstream to fuel their ability to fly to the next flower. In that way, “energy is always available,” says Valentina Peña, a colleague of Camacho’s who’s starting her Ph.D. in ecology and evolutionary biology at UC Irvine this fall.
We’re not unlike the bats. Exercise impacts the way we handle sugar, too, which is why Camacho is curious about the connection between flight and a bat’s ability to metabolize a lot of sugar.
In particular, she wants to know which molecules the bats are using during exercise to regulate their blood sugar in order to bring their glucose levels down. And she’s curious about how they protect their bodies from accumulating the kind of damage to their cells and DNA that usually comes from digesting a lot of sugar.
“Maybe that can teach us some things about how to be healthier in our lives,” explains Camacho, including — perhaps — how to treat or even prevent the onset of obesity and type 2 diabetes. “There’s a lot that we can learn from how they’ve come to thrive on the sugar diet.”
The sweetest of puzzles
Camacho has been letting the bat that she fed earlier rest for a few minutes. She now wants it to fly around the tent so she can sample its blood for any of those molecular clues about how it processes sugar to fuel its flight.
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She needs the bat to fly for about ten minutes, but after a minute or so, the bat lands on the side of the tent. “Not every bat cooperates,” she says.
Camacho and Peña try another one of the same species. Unlike his colleague, this bat soars into the air and doesn’t stop flying — for 15 minutes.
Camacho is ecstatic. “Oh, what a beautiful bat,” she coos. “I love him!”
After catching him in a net again, Camacho and Peña take a blood sample. She’ll freeze some of it to study in the lab later. But then Peña touches a glucose meter — the kind that people with diabetes use to measure their blood sugar levels — to a drop of the bat’s crimson blood.
Camacho is floored. “Damn!” she exclaims. “I can’t believe you.”
She figured the glucose level would have dropped, as it has in similar experiments in the lab conducted by other researchers. But even after 15 minutes of flying in this more natural environment, it’s still so elevated, she can’t measure the change. The bat’s maxed out the meter, so the display just reads “high.” If a person had such a reading for long enough without medical intervention, they’d expire.
“This doesn’t make sense,” she says with a mix of disbelief and admiration. "Why aren't you dead?"
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