Why salty food actually makes you less thirsty
IF a salty meal has you reaching straight for a glass of water, it’s not for the reason you might think.
the idea that salty food makes you thirsty could be an old wives’ tale, scientists have found.
In a study carried out during a simulated mission to Mars, researchers discovered that people who ate more salt retained more water and were less thirsty.
the German researchers set out to examine how much water people would need on a long spaceflight and measured how their food intake affected this.
People may want to drink immediately after eating salty food, but this is simply to wash the taste of salt from their mouth. Overall, they will drink less if they consume more salt, the scientists found.
the researchers, from the German aerospace centre, tested the impact of diet on volunteers sealed into a mock spaceship for up to seven months.
every aspect of their water consumption and salt intake was controlled and measured.
One group of ten men was examined for 105 days, and a second for 205 days. they were given three different levels of salt in their food. the scientists, whose work is pub- lished in the Journal of clinical Investigation, found that more salt in the diet caused the subjects to drink less, triggering a mechanism to conserve water in the kidneys.
Until now scientists believed the charged sodium and chloride ions in salt grabbed on to water molecules and dragged them into the urine – using up water and making us thirsty.
But the new results showed something different – salt goes into the urine, while water passes back into the kidney and body.
the findings alter the understanding of the role that urea, one of the key components in urine, plays in our bodies.
Professor Friedrich Luft, managing director of the charite University Hospital in Berlin, said: ‘It’s not solely a waste product, as has been assumed. Instead, it 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.’
a second set of experiments, carried out on mice, found that this process also uses up a lot of energy. this means that eating salt also stimulates hunger, a trend seen among the astronauts as well. the discoveries change the way scientists think about the process by which the body achieves water homeostasis – maintaining a proper amount and balance.
Professor Jens titze, of the University of erlangen, said: ‘We now have to see this process as a concerted activity of the liver, muscle and kidney.
‘While we didn’t directly address blood pressure and other aspects of the cardiovascular system, it’s also clear that their functions are tightly connected to water homeostasis and energy metabolism.’