An international group of scientists tested the theory by monitoring the salt intake and hydrating levels in cosmonauts during a year-long simulated mission to Mars.
After the study, researchers concluded that the adage could not be further from the truth. In fact, they found that food with lots of salt quelled thirst, making cosmonauts more hydrated and energetic.
The study will change the way scientists look at urea in the body. Once seen as simply a wasteful protein excreted in urine, it may turn out to be a valuable body product.
The decision to test the theory in space had two benefits:
One, It is useful information for cosmonauts. Hydration is important on long space voyages, where food and drink are rationed.
For cosmonauts to efficiently organize their food stock and remain healthy, space teams need to determine the relationship between salt and liquid consumption accurately.
Secondly, space provided an entirely controlled environment. Every aspect of a person's water use, nutrition, and salt intake could be calculated and calibrated during the simulation.
The test subjects were two groups of ten male volunteers. The volunteers were sealed into a mock spaceship for stimulated flights to the red planet.
The first batch was studied for 105 days, while the second one was examined over 205 days.
The two groups had identical diets, except that over periods lasting several weeks, they were provided with three different levels of salt in their food.
The test results showed that eating more salt leads to a higher salt content in urine.
However, the increase was not due to more drinking. Salt was triggering a body mechanism to conserve water in the kidneys.
Salt remained in the urine, while water moved back into the kidneys and body.