This episode is sponsored by Wren, a website that  helps fund projects to combat the climate crisis.

Click the link in the  description to learn more about how you can make a monthly contribution to support projects like  rainforest protection programs. [♪ INTRO] Floating around in space sounds amazing. Like, there’s a reason people  pay thousands of dollars to go on zero-G flights.

But when it comes to being a weightless astronaut, there’s a catch: If astronauts don’t exercise  for two hours a day or more, they risk debilitating muscle loss. In microgravity, muscles in the neck, back, and legs just don’t need to work  as hard to support a person. So without regular, full-body exercises, those muscles can waste away on even  a one- or two-week stay in space.

Except, here’s the thing: There are some animals on Earth that can  go an entire winter with limited movement, nd then wake up in the spring  fit, healthy, and ready to go. I’m talking of course about hibernation. And it turns out that studying one  hibernating animal in particular could help us humans fight muscle  atrophy on long space flights: Ground squirrels.

Now, you might think bears are an obvious   model for this kind of long, chill slumber:  They’re large, omnivorous mammals like we are. And we have learned some things byl studying them. For instance, scientists believe that  hormones like testosterone and estrogen, which help regulate metabolism, also  help bears preserve muscle mass.

They also think that genes governing protein  synthesis in the muscles are involved.   Based on this, scientists have tried  manipulating similar genes in lab mice, which don’t hibernate, to see if that would  also preserve their muscle mass in space. In this 2020 experiment, mice sent  to the International Space Station were injected with a drug that blocked a  gene involved in regulating muscle growth. It was like the researchers shut  down an “off” switch in the mice .

So, by blocking this gene, they  actually stimulated muscle growth. as a result, the treated mice showed  less atrophy than untreated animals after their stay on the ISS.   Unfortunately, just injecting  some hormones or toying with genes in a human astronaut isn’t a very practical  solution to our muscle loss problem. Hormones and genes can affect  so much that modifying them just to prevent muscle loss  could have long-term consequences we don’t fully understand. Also, we still have a lot  to learn about what exactly is happening in bears when they  take that long winter break.   So, although some scientists are  still working on bear research, others are also looking at different mammals to get an idea of how they maintain  muscle mass over their hibernation period.

And that’s where squirrels come in. Thirteen-lined ground squirrels, specifically.   These striped and spotted squirrels live  in the central United States and Canada, and they typically hibernate for a full  five or six months over the winter. They wake up in the spring just in time for mating  season, where they need their physical fitness.   How do they do it?

Turns out, these squirrels  have got the guts for it. Literally. The microbes in their guts help them maintain   elevated levels of protein synthesis  that keeps muscles from wasting away.

The key thing is how those microbes handle urea. Urea is a waste product that’s rich in nitrogen, and it normally accumulates in  urine and is released from the body. But these gut microbes metabolize urea: They turn the nitrogen back into  a form that both the microbes and the squirrel can use to build proteins.

This helps prevent the urea  from building up in an animal that isn’t going to the bathroom all winter, and it gets both parties an important resource. This process happens all year, but  the microbiome ramps up this activity during the hibernation period,  when the squirrel is fasting and not actively eating a normal diet.   And it was pretty simple for  scientists to figure this out, too. In one experiment published in  2022, they treated squirrels with antibiotics to wipe out  their standard gut bacteria.

And when they did, they saw less protein  synthesis happen in the squirrels’ muscles. This nitrogen recycling may also happen  in other animals, including bears, but scientists will need  more data to know for sure. And either way, the great news is  that there’s a hint that this strategy could actually be a practical  approach for humans.   Scientists have been investigating  nitrogen salvage in humans for at least half a century, and they’ve found some encouraging data.

For instance, a 1992 study showed  that people on a low-protein diet increased their gut nitrogen salvage in a similar way to those fasting squirrels. That said, there are a lot  of unanswered questions. Like, we don’t know if nitrogen  salvage in humans could be enough to stave off muscle loss, or how to get this change without  a restrictive low-protein diet.

We also don’t know which bacterial strains   are the best candidates for this job. Still, understanding how the process works in other animals brings us  one step closer to creating a supplement that could promote this  kind of gut microbiome in humans. It would be great for helping people who  are bed-ridden or malnourished here on Earth to preserve healthy muscle mass.

Or it could just be an aid for the demands of growing children or pregnant people. And maybe in the future, if you board that long-distance shuttle to Mars, a special diet or a little probiotic  pill could help you stay healthy and fit on your trip to deep space… without having to do so much exercise. But before we leave it behind, we’ve got to make sure our planet is healthy, too.

That’s why this episode is sponsored by Wren, a website where you calculate  your carbon footprint, then offset it by funding projects that  plant trees and protect rainforest. On their website, you can answer a  few questions about your lifestyle so you can see what your carbon  footprint is, and how you can reduce it. No one can reduce their carbon footprint to zero, so you can offset what you  have left after reducing.

Once you signup to make a monthly contribution to offset your carbon footprint, you receive monthly updates from promising  carbon removal, rainforest protection and other projects you support. You also get to see the trees you planted, nd what your money is spent on. We’ve partnered with Wren  to plant 10 additional trees for the first 100 people who  sign up using our referral link!

Check out the link in the description,  and thanks for supporting SciShow. [♪ OUTRO]