It sounds obvious. When you eat something salty, you feel thirstier and find yourself gasping for water. But a surprising new study has found that, in the long term, that’s not always the case.
The research, published in The Journal of Clinical Investigation, was carried out by the Max Delbrück Center for Molecular Medicine (MDC) in Berlin, Germany, and other institutions. They studied 10 men who took part in two simulated flights to Mars on Earth, one lasting 105 days and the other 205 days. Over a period of weeks, they were given diets with different salt contents.
The importance of the research for Mars missions is that, on long-duration space missions, the diets of the astronauts will have to be strictly controlled. Thus, it’s important to know the effects salt has on the human body.
Previously, salt consumption was thought to be linked to an increase in the production of urine, as people drank more liquid. But this study suggests the increase in urine does not come from more drinking, but rather that salt was triggering a mechanism to conserve water in the kidneys. And in the long term, it might make a person drink less.
“Before the study, the prevailing hypothesis had been that the charged sodium and chloride ions in salt grabbed onto water molecules and dragged them into the urine,” a statement from the MDC read. “The new results showed something different: salt stayed in the urine, while water moved back into the kidney and body.”
Missions to Mars may require novel approaches to diet. NASA/Pat Rawlings
Studies in mice have found that a high-salt diet actually increases hunger, not thirst. The human participants in this latest study also said they were hungry after a salty diet. It’s further suggested that urea from urine might actually keep water in our bodies when we get rid of salt.
“Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt," said Professor Friedrich C. Luft from the MDC in the statement.
Thus, it’s suggested that in the long term, a salty diet may actually make us less thirsty than a lower salt diet. However, in the short-term, we still experience drinking responses that make us drink more.