Think Salt Makes You Drink More? Think Again

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Everyone knows salty foods makes you thirsty, drink more water (or beer), and pee more, right? Maybe not. A new German study, conducted during a mock mission to Mars, turns this long-held assumption on its head. It turns out salt might make us crave more food, not fluids.

If this study sounds a little weird, well, it is. But simulated space travel is actually a great means of testing how salt impacts the body, because when on these extended flights, volunteers’ bodies conserve every last bit of water possible. Plus, this controlled environment lets researchers carefully monitor everything that goes into and out of their bodies.

As part of the Mars500 project, which sent one small group of men into "space" for 105 days and another for 205 days, scientists investigated how sodium affected the amount these guys drank and peed. They fed both groups the same menu throughout, except during weeks-long stretches, when they’d tinker with the salt levels in the food.

When the data came in, the men did, in fact, drink more fluids immediately after eating the saltier foods. However, they consumed less water overall. And yet, they still peed more — and had saltier urine. So clearly, increased urine production was unrelated to total fluid intake, contradicting previous thinking.

According to the researchers, the reason the men peed more after eating saltier foods likely has to do with urea. This substance, which is formed in the kidneys and muscles, helps rid the body of nitrogen. But animal studies suggest that urea may also hold water in the body while flushing sodium out. If that’s also the case in humans, it would explain the astronauts’ saltier urine.

But it takes energy to produce more urea to combat excess salt. That may be why, in animal studies, mice fed salty diets have consumed more food. It might also explain why the human volunteers in this trial complained of hunger when given the saltier diet. By this logic, the researchers suspect that rather than induce thirst, sodium-heavy foods make us hungry.