Does a salty diet actually make you thirsty?

Salt is an essential part of most of our diets. Serving as a flavour enhancer, salt is an important part of digestion, as it increases the hydrochloric acid content of our digestive fluids.

But salt has also gained a bad reputation causing ill effects on our heath due to excessive consumption.

One of things we’ve heard for a long time is that salt makes your thirstier. But it turns out that this is not true.

A study conducted by a group of scientists during a simulated mission to Mars, found that “cosmonauts” who ate more salt, retained more water and weren’t as thirsty but needed more energy.

It seems that the salt was triggering mechanisms which led the kidneys to conserve water while the salt stayed in the urine.

Scientists have known for a long time that salt intake activates the production of more urine and it was assumed that the extra fluid came from drinking.

But now researchers from the German Aerospace Center (DLR), the Max Delbrück Center for Molecular Medicine (MDC), Vanderbilt University and colleagues around the world, tested the hypothesis that an increase in salt intake of 6 g/d would change fluid balance in men living under ultra-long-term controlled conditions.

And this is where the simulated mission to Mars comes in. It provided the environment needed to measure and control every aspect of a person’s nutrition, water consumption and salt intake.

For this study, 10 healthy men were sealed into a mock spaceship over two simulated flight missions of 105 days and 205 days. Both groups had identical diets except over several periods lasting a few weeks when they were given three salt intake levels (12, 9, or 6 g/d).

The results confirmed high salt intake led to a higher salt content in urine and re-established the correlation between the amount of salt and overall quantity of urine.

However, the increase did not seem to be due to more drinking or thirst. The salty diet caused the participants to drink less water. It seems that the salt was triggering mechanisms which led the kidneys to conserve water while the salt stayed in the urine.

These finding were in contrast to the previous hypothesis that the charged sodium and chloride particles dragged water molecules into the urine.

In another study, mice were given a high salt diet which increased the urea accumulation in the kidney, where is counter-acts the water drawing properties of sodium and chloride.

Urea is a substance which is found in muscles and liver and helps in shedding nitrogen.

Synthesizing urea take a lot of energy, which explains why mice on a high salt diet were eating more. The participants from the space mission study on a high salt diet also complained about being hungry.

This has revised scientists’ view of urea and its function It is not a waste product but an important osmolyte, a compound that binds to water and helps transport it. It helps to keep water in our bodies when we get rid of salt in our urine.

Now that we know salt triggers hunger pangs, perhaps not over consuming salt may benefit our body even more, unless you were off to Mars.

Source: Journal of Clinical Investigation, Journal of Clinical Investigation