For years, the calculation has been simple: Salt makes you thirsty. That's the operating principle behind bar snacks, at least, and the common wisdom about why downing a bag of Doritos will leave you feeling parched and weird. But it turns out that operating wisdom is wrong, though it might explain why it's hard to stop hitting the Pringles once you start. Salt doesn't make you thirsty. It actually makes you hungry. Scientists found out this crucial bit of information through a simulated mission to Mars, in which all food and drink consumed by the participants was carefully monitored. A potential trip to Mars has many questions, and one of them is how to provide food in the longterm for the astronauts taking part. 

In the experiment, as reported in The Journal of Clinical Investigation, two groups of ten male volunteers were sealed into a pretend spaceship to simulate a trip to Mars. One group stayed in the simulation for 105 days, the other for 205 days. They ate identical diets, except for varying levels of salt in their rations. Results from the experiment showed that those who ate salt had more salt in their urine, unsurprisingly. But countering the common wisdom that salt equals thirst, those that ate the salty diet actually drank less fluid. Apparently, salt triggers the kidneys to hold onto water and produce more urea, which made the subjects hungry rather than thirsty. 

"Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt," wrote the study's co-author Dr. Friedrich C. Luft. So there you go. Those pretzels are not, in fact, making you thirsty.