How combat athletes shed and regain water weight

HostIf you ever see a fighter on the scale the day before a big match, they look almost scary. Their skin looks paper thin, like it's wrapped tight over their bones. You can see every single muscle fiber and even the beat of an artery in their neck that you would never normally see. It's a look that seems impossible to maintain for more than a few minutes. I have always wondered how they pull that off without falling over right there on the stage.

GuestWell, the secret is that they're not actually trying to lose weight in the way we usually think about it. They're not burning off fat or losing muscle. They're just moving water around. The human body is mostly water, and water is heavy. One single gallon weighs about eight pounds. So if you can find a way to dump a few gallons of fluid out of your system, you can drop ten or fifteen pounds in just a few days. They call it the cut. The goal is to hit a very specific number on the scale for just a few seconds, and then they immediately start trying to put it all back on.

HostBut where's all that water hiding? I mean, it's not like they're just full of empty space.

GuestIt's mostly stored in these little energy bundles in your muscles called glycogen. Think of these as tiny water sponges. For every bit of energy stored in those sponges, the body packs in three or four times that much weight in water. To dry those sponges out, the athlete stops eating any carbs and works out hard to burn through what's already there. As the energy gets used up, the sponges shrink and all that tied up water gets sent to the kidneys to be peed out.

HostSo they just stop eating bread and run a lot? That sounds like a normal diet, just faster.

GuestIt's much more aggressive than a diet. There's a lot of biological trickery involved. A few days before the weigh in, they actually start drinking a massive amount of water, like two or three gallons a day, and they eat a lot of salt. This sends a signal to the body to stop making a hormone called aldosterone. That hormone is what tells your kidneys to hold onto salt and water. When you flood the system like that, the body basically flips a switch to flushing mode. It gets very good at getting rid of fluid because it thinks there's an endless supply coming in.

HostOkay, but if they're drinking three gallons a day, they must be gaining weight, not losing it.

GuestAt first, yeah. But here is the trick. About twenty four hours before they have to step on the scale, they suddenly stop drinking entirely and cut out all the salt. But the body is slow to react. It stays in that flushing mode for a little while longer. The kidneys keep working overtime even though no new water is coming in. They're basically tricking the body into peeing out water it actually needs to keep. They can drop several pounds just while they're resting because the body hasn't realized the tap has been turned off yet.

HostThat sounds like it would start to feel pretty bad. Is that when the paper thin skin happens?

GuestThat's the start of it, but the last few pounds are the hardest. To get those, they have to use heat. They sit in saunas or hot baths or wear heavy plastic suits while they exercise to force themselves to sweat. This is where it gets dangerous. At this point, there's no more easy water to lose, so the body starts pulling fluid out of the blood plasma. When that happens, the blood gets thick. It becomes viscous, almost like syrup. The heart has to work much harder to pump that thick blood through the veins to get oxygen to the rest of the body.

HostI imagine that would make you feel pretty lightheaded.

GuestIt's worse than just feeling dizzy. That fluid also acts as a cushion for the brain. It's called cerebrospinal fluid. When you're that dried out, you lose some of that buffer. If a fighter actually tried to go into the ring in that state, a single punch to the head could be deadly because the brain doesn't have its usual padding to soak up the blow. That's why the weigh in happens a full day before the actual fight. They need that time to undo all the damage they just did to themselves.

HostCan they really just drink a bunch of water and be fine by the next night?

GuestNot exactly. You can't just chug water as fast as you can. The gut can only handle about one liter of fluid every hour. If you drink way too much plain water too fast, it can actually be toxic and your body will just flush it right back out again. To get the water back into the cells where it belongs, they have to use a specific trick. They use a very precise mix of salt and sugar. This triggers a special pump in the small intestine called the SGLT1 transporter.

HostA pump? How does a bit of sugar act like a pump?

GuestIt's like a biological vacuum. When the salt and sugar hit that part of the gut together, it forces the body to pull water through the lining of the intestine and straight back into the bloodstream and muscles. It's much faster than just waiting for the water to soak in on its own. By using that specific ratio, they can pull every drop of fluid back into those dried out sponges. Most fighters will gain back every ounce they lost, and sometimes even more, in the twenty four hours before the bell rings.

HostIt's wild to think they're basically a completely different weight by the time they actually start the fight.

GuestIt's a total transformation. They go from being so dried out that you can see their pulse through their skin to being full of fluid and strength again in just one day.

HostThe next time I see a fighter looking like a skeleton on the scale, I'll be thinking about those tiny sponges in their muscles waiting for that hit of salt and sugar to puff back up.

HostThat's a lot of work just to change a number for a few seconds.

GuestEvery ounce of that weight is just a temporary move to beat the system.

HostThose paper thin muscle fibers are just a sign that the body is waiting for the pump to turn back on.

GuestExactly.