Ask pretty much anyone and they'll tell you that eating salty foods makes a person thirsty. Alas, here's a reminder that just because a belief is held by basically everyone you can and will ever know doesn't mean it's actually true.
Now, a pair of studies, the results of which both appear in the current issue of The Journal of Clinical Investigation, has found that eating salty food doesn't actually make you thirsty in the long run—but it can make you hungry.
And all it took to find that out was a simulated mission to Mars.
A group of researchers—from institutions including the German Aerospace Center, the Max Delbrück Center for Molecular Medicine, and Vanderbilt University—put two groups of ten male volunteers into a sealed mock spaceship for two simulated flights to Mars. Group number one was examined over a period of 105 days, and group number two was studied over 205 days. The men all ate identical diets, except they were fed different levels of salt in their food.
The results showed that those who ate more salt had a higher salt content in their urine and produced a higher quantity of urine—no surprise there. What did surprise the researchers was this: The subjects who ate more salt did not actually drink more water—in fact, those who ate the saltier diets actually drank less water. In addition, the human "cosmonauts"—the scientists' term, not ours—who ate the saltier diets complained more about being hungry. So salt made the test subjects feel hungrier, but not thirstier.
These findings made the scientists rethink several long-held notions.
It was previously thought that salt, in effect, grabbed water molecules and brought them into the urine. But the new study showed that the salt stayed in the urine, while the water recirculated back into the kidney and the body.
The study caused the scientists to re-assess the function of urea: "It's not solely a waste product, as has been assumed." Professor Friedrich C. Luft of the Max Delbrück Center, explained: "Instead, [urea] turns out to be a very important osmolyte—a compound that binds to water and helps transport it. Its function is to keep water in when our bodies get rid of salt. Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt."
In the end, the study changed the way the scientists view homeostasis—the function by which the body maintains a proper amount and balance of fluids.
Does this mean that the entire industry behind the nuts they serve at bars will collapse in upon itself? Only time will tell.