Your friend may be onto something. While eating excess salt in everyday life can cause bloating, not having enough of it can cause swelling too. And it’s far more likely your sodium levels are on the low side after hiking all day.
It’s possible, if you don’t take in enough salt while you’re hiking but drink a lot of water, to dilute the sodium levels in your body to unsafe levels. When that happens, you have hyponatremia, and one of the symptoms is—you guessed it—puffy hands, because the extra water in your system enters your cells and causes them to swell. But should you OD on water and forget the salt, you’ll likely experience other symptoms of hyponatremia as well, including “headaches that won’t go away, confusion that your friends recognize, but you might not, irritability, swollen feet and ankles,” says Dr. Bob Murray, the founder of Sports Science Insights, LLC, and the former director of the Gatorade Sports Science Institute.
(How much water is too much? Everyone’s needs are different. At rest, the average set of kidneys can handle up to a liter of liquid per hour, according to Scientific American. But while you’re exercising, that amount can fall drastically, because your body releases an anti-diuretic hormone that lowers the kidney’s excretion capacity.)
“If you get puffy hands, you don’t want to disregard it,” Murray says. “But nine times out of 10, it’s just fluid pooling in the hands.”
And that’s the other, much simpler explanation for your Michelin Man hands: blood is pooling in them. This is usually not a big deal, and the problem should resolve within a few hours after your hike. But if your fluffy fingers are really bothering you, try lightening your load. The straps of your backpack can “further reduce return venous blood to the heart,” Murray says, so it may help to cut down your pack’s weight. Murray also recommends holding your hands over your head periodically, stopping to pick things up, and making fists to help move the blood back toward the heart.
THE BOTTOM LINE: If you feel fine, your puffiness is likely due to the pooling of blood in your hands. But if you have any of the symptoms of hyponatraemia, your sausage fingers might be the sign of a serious electrolyte imbalance, indicating that you need to take in more salt.