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posted by Fnord666 on Wednesday April 19 2017, @08:43PM   Printer-friendly
from the give-up-the-pork-rinds dept.

We've all heard it: eating salty foods makes you thirstier. But what sounds like good nutritional advice turns out to be an old-wives' tale. In a study carried out during a simulated mission to Mars, an international group of scientists has found exactly the opposite to be true. "Cosmonauts" who ate more salt retained more water, weren't as thirsty, and needed more energy.

For some reason, no one had ever carried out a long-term study to determine the relationship between the amount of salt in a person's diet and his drinking habits. Scientists have known that increasing a person's salt intake stimulates the production of more urine -- it has simply been assumed that the extra fluid comes from drinking. Not so fast! say researchers from the German Aerospace Center (DLR), the Max Delbrück Center for Molecular Medicine (MDC), Vanderbilt University and colleagues around the world.

[...] 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. The new results showed something different: salt stayed in the urine, while water moved back into the kidney and body. This was completely puzzling to Prof. Jens Titze, MD of the University of Erlangen and Vanderbilt University Medical Center and his colleagues. "What alternative driving force could make water move back?" Titze asked.

Experiments in mice hinted that urea might be involved. This substance is formed in muscles and the liver as a way of shedding nitrogen. In mice, urea was accumulating in the kidney, where it counteracts the water-drawing force of sodium and chloride. But synthesizing urea takes a lot of energy, which explains why mice on a high-salt diet were eating more. Higher salt didn't increase their thirst, but it did make them hungrier. Also the human "cosmonauts" receiving a salty diet complained about being hungry.

So, to reduce your portions and lose weight, eat less salt?


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  • (Score: 0) by Anonymous Coward on Thursday April 20 2017, @01:11AM (1 child)

    by Anonymous Coward on Thursday April 20 2017, @01:11AM (#496631)

    > We've all heard it: eating salty foods makes you thirstier.

    TFA discusses a long term study. We use very little added salt in home cooking (but not 0 salt) and have gotten used to other savory & spicy flavors. Sometimes when eating out we get a fairly salty dinner--and short term this certainly makes me very thirsty. So the "old-wives' tale" may have some truth to it. There are often large differences in short and long term effects, many systems are not linear.

    Personal observation, if I start eating some salty chips every day, my blood pressure (using same machine at supermarket) jumps about 10 points within a week. Once I back off, the blood pressure goes back down within a week.

  • (Score: 0) by Anonymous Coward on Thursday April 20 2017, @03:32AM

    by Anonymous Coward on Thursday April 20 2017, @03:32AM (#496676)

    A significant percentage of people are salt sensitive that way. But a lot of people aren't. Low salt consumption for the latter group might be harmful for them:
    https://well.blogs.nytimes.com/2016/05/25/a-low-salt-diet-may-be-bad-for-the-heart/?_r=0 [nytimes.com]

    Among 69,559 people without hypertension, consuming more than seven grams of sodium daily did not increase the risk for disease or death, but those who ate less than three grams had a 26 percent increased risk for death or for cardiovascular events like heart disease and stroke, compared with those who consumed four to five grams a day.

    In people with high blood pressure, consuming more than seven grams a day increased the risk by 23 percent, but consuming less than three grams increased the risk by 34 percent, compared with those who ate four to five grams a day.

    Perhaps only those taking low salt diets were sicker in the first place? But if that was controlled for then various groups have been giving bad dietary advice for decades e.g. the FDA's recommended salt consumption is 2.3grams which is a lot lower than four grams a day.