Salt makes you want to drink less and eat more, Mars simulation study finds

The World Health Organization (WHO) recommends adults consume less than 5g of salt a day – that's less than one teaspoon. Getty Images

Consuming salt does not make you thirsty – but it does make you hungry, a new study suggests.

Eating salt is known to stimulate the production of urine, a fact that had many in the scientific community believe that salt makes one thirstier. However, it’s a myth that has now been busted in a Mars spaceflight simulation study led by researchers at the Vanderbilt University Medical Center in the U.S. and the Max-Delbrueck Center for Molecular Medicine in Germany.

To find this out, scientists kept 10 healthy men within sealed living quarters and fed them a controlled high-salt diet for 205 days.

READ MORE: Are low-salt diets bad for your heart? This Canadian study is stirring up controversy

The men were observed drinking less and retaining more fluid within their bodies, even though they were producing more urine, over the long-term.

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However, when the men were given food with higher salt levels, they reported feeling hungrier.

The study was then repeated on mice, which yielded the same results.

The kidneys, researchers say, act like a “biological barrier designed for water conservation that is able to separate osmolytes from water to prevent dehydration while conducting osmolyte balance.”

(According to the Helmholtz Association, osmolytes are a compound that binds to water and helps transport it.)

Put simply, salt triggered a mechanism to conserve water in the kidneys.

“[Urine] is not solely a waste product, as has been assumed,” Friedrich Luft, co-author of the study, said in a statement. “Instead, it turns out to be a very important osmolyte … Its function is to keep water in when our bodies get rid of salt. Nature has apparently found a way to conserve water that would otherwise be carried away into the urine by salt.”

But the body’s fluid production does not determine the amount of fluid it can consume as a liquid or in food, researchers add. This happens because the body uses the fluid to create energy, which then produces carbon dioxide and water that the body can rid itself of.

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So, what does salt have to do with space travel and Mars?

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“A long space voyage conserving every drop of water might be crucial,” researchers said in a statement. “A connection between salt intake and drinking could affect your calculations – you wouldn’t want an interplanetary traveller to die because he liked an occasional pinch of salt on his food. The real interest in the simulation, however, was that it provided an environment in which every aspect of a person’s nutrition, water consumption and salt intake could be controlled and measured.”

As for what this means for us humans down here on Earth, it could change the way scientists see the human body and how it works.

“We now have to see this process as a concerted activity of the liver, muscle and kidney,” study co-author Jens Titze said. “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 (maintaining a proper amount and balance of water) and energy metabolism.”

READ MORE: Hold the salt: Packaged foods with the highest and lowest sodium levels

The study was published in the Journal of Clinical Investigation.

However, several studies throughout the years have warned against eating high amounts of salt.

A 2009 study published in BMJ concludes that a high salt intake is directly linked to stroke and cardiovascular disease.

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The World Health Organization (WHO) recommends a level of salt consumption of five grams (or one teaspoon) a day. However, most people in Western countries consume close to 10 grams per day.

After looking over 13 published studies that included over 170,000 people, researchers found that a difference of five grams a day in salt intake is linked to a 23 per cent increase in the rate of stroke, and a 17 per cent increase in the rate of cardiovascular disease.

The Institute for Quality and Efficiency in Health Care also found a correlation between reduced salt intake and lowered blood pressure in 2009, while a 2015 study by the Federation of American Societies for Experimental Biology reported a possible link between higher salt intake and the development of multiple sclerosis (MS).

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