Salty Food Might Make You Drink Less, Not More

You can thank a future trip to Mars for a surprising new theory on how salt affects the body

Mmmmmm ... pretzels. kr1sta via iStock

Sometimes it just takes some fries or a bag of chips or pretzels to really hit the spot. But all that salt is bound to leave you reaching for a tall glass of water, leading many to believe that eating salt means you're drinking more overtime. But you might want to put down that glass of water and listen up: As The Independent’s Ian Johnston reports, new research suggests that salt makes you drink less in the long term—and that it could make you eat more.

The finding goes against common wisdom, but it’s supported in a pair of new papers in the Journal of Clinical Investigation. Researchers thought that if they increased the salt intake of men living under controlled conditions, they would need to drink more and would produce more urine.

But that’s not what happened. When the men were given more salt, they drank less fluid in the long term, not more. They also urinated less, suggesting that their bodies were holding on to water. And when the researchers did the same thing with mice, the mice showed the same results.

The study was made possible by the intense micromanagement of a long-term Mars simulation in which every iota of food subjects ate was controlled—and every drop of urine that left their bodies collected. One test period spanned 105 days, the other 205 days of a trip simulation, in an attempt to figure out what might happen to humans during the lengthy venture to and from the Red Planet.

Scientists have long thought that when the body takes in too much salt, it ups urine production to excrete it, thereby losing water along the way, making people even thirstier. But that wasn't exactly what was happening. Overtime, the subject seemed to retain the water. 

“These amounts are small; you will not notice them at the urinal. However, it takes 510 days to get to Mars and back,” Friedrich Luft, a researcher who was part of both studies, tells Johnston.

The counterintuitive findings suggest that scientists have been thinking about salt intake wrong. Instead of losing water in response to higher salt intake, the body may hoard it—and that might have bigger implications. This retention of water is an energy-intense process, which suggests that with higher salt, the body must break down muscle proteins to compensate.

The men on the high salt diet also reported being more hungry, writes Johnston. Some of the hormones spotted in the mice after increased salt intake, glucocorticoids, are thought to affect hunger and are associated with diabetes and obesity. And if salt really does make people hungrier, it might mean that salt plays a bigger role in things like metabolic syndrome than previously thought. 

The need to take in more energy or lose muscle mass in an attempt to hold on to water “predisposes to overeating,” says Jens Titze, who co-authored the study, in a press release. More work must be done to figure out exactly how salt contributes to the body’s complex metabolic processes, but the study suggests yet another reason to take a pass on that pile of French fries.

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