Eating Salty Food Doesn't Make You Thirstier, Says Haifa Scientist

Should we eschew salt before Yom Kippur? Not necessarily, according to a recent study involving students and nuts by Prof. Micah Leshem of Haifa University.

Some things seem self-evident: wear tight shoes, your toes will hurt. Eat salty foods, you will crave water. Not so?

Not necessarily, it seems. You may want a drink because of the dry mouth-feel after eating salt, not because your body physiologically aspires to correct its hydromineral balance, postulates Prof. Micah Leshem of Haifa University, based on an admittedly small study involving students and nuts.

In other words, bars that set out bowls of free salted snacks in the hope that their sodium-saturated customers will be biologically induced to drink more are wasting their own money, according to Leshem's findings.

Eat, drink and pee?

"Everybody 'knows' that when you eat salt, you become thirsty," Leshem, a professor in the Department of Psychology, told Haaretz. "But that's what we were investigating here – whether in fact salt makes you thirsty."

The experiment involved 58 students, who underwent testing every few days, following a two-hour abstention from water (and cigarettes). They were divided into three groups. One was given salted nuts, one unsalted nuts and one sugar-coated nuts. The amount of salt in the salted snack was between 30% to 40% of the daily intake, roughly speaking.

Then, during a couple of hours in which the students responded to various questionnaires with bottled water freely available, they rated their own level of thirst every 15 minutes. Their water intake was measured without their knowledge.

The results of this "voluntary, acute intake of a sodium  load" are described in Leshem's paper, published in Appetite www.elsevier.com/locate/appet.

Neither the thirst the students reported nor the actual quantity of water they drank was any different after eating salty nuts than after eating unflavored or candied ones. (Why test sugary nuts too? To make sure differences weren't due to changes in taste, Leshem explains.)

Leshem did not set out to test whether, over time, people who eat more salt drink more. He set out to see whether people who eat a salty solid will want to drink more water than people who ate something else.

Dear reader, they did not. Or, in the argot, "our study found little support for the assumption that salt invariably increases drinking,” Leshem stated.

Micah Leshem

Treacherous terrain of the Salt Wars

Shouldn't it, physiologically? That leads us into the bloody terrain of the Salt Wars: Is salt good or bad for you?

"We can put men on the moon but don't know if salt is good or bad for you," Leshem helpfully sums up. "Some say it's clear that it's bad and some say it doesn't do anything to you in normal quantities."

Some argue that consuming salted foods causes you bloat because one drinks more, whether water or worse, soda; and may become obese. Leshem doesn't buy that one: any excess salt we eat, or water we drink, doesn't stay in the body. It gets urinated out, and our sweat will become saltier. 

"There are a lot of options to maintain the balance of sodium and water in our bodies," he says, and his student study indicates that immediately heading off to stick one's face in the water cooler after eating peanuts isn't one of them. He also points out that our ancestors and life forms in general couldn't and can't just amble over to the fridge for a cool drink; they had to evolve systems to redress their hydromineral balance that did not involve immediately imbibing.

Hankering for the primordial sea

There is a theory that the balance of salt and water in the human body is what it is because of the primordial sea, where life started, and where the salt concentration was about 0.9% - which is exactly that of our body. It could be coincidence. But, to pursue the theory, as life left the sea for dry land, it had to evolve salt-equilibrium mechanisms. (For an alternative theory: Is the sodium chloride level in the oceans evidence for abiogenesis?)

We humans, for all our pretentions and inventions, are merely leaky skin-coated bags of primal sea, Leshem explains happily: and it is that inner concentration that we are maintaining when we eat salt to replenish its loss by that leakage – in urine, in sweat, in feces, and in injury and ailment. We are especially leaky when we are born, and every neonatologist is on the lookout – many newborns require salt supplementation to survive and develop fully.

"The first thing to do is to maintain that," he sums up. "Only one thing kills us more quickly than lack of salt or water – lack of oxygen. Without that you can die in minutes. If you don't eat salt or don't drink, you could die within hours."

So we need to eat salt. How much? Stay tuned, because even the iconic U.S. Institute of Medicine is confused enough to have backtracked on its original recommendation, dating from decades ago, to "reduce" sodium input, although the Institute of Medicine isn't saying that salt is good.

"High salt intake may be unhealthy, but there's no good evidence that reducing it helps," says Leshem.

Maybe that's just as well. Data from 2010 shows that worldwide, in general, people eat about twice as much salt as they should 0– albeit that "should" is controversial itself. Armenians were found to have the heaviest salt habit in the world (about 5 grams a day) followed by their neighbors in central Asia.

So should you eschew salt before Kippur?

So, should Yom Kippur fasters forgo salt in the pre-fast meal, as some dietitians recommend? Eat more? Ignore the whole thing?

"Dear Kippur fasters – do not skimp on your salt, and don't overdo it," Leshem spells out. "Salt and water are both necessary to survive the fast properly. Not enough salt, like too much, may dehydrate you more than necessary, and too much water might do the same! So eat and drink as you are used to. Don't overdo it."

Extra food and water you eat in advance won't ultimately make any difference: "You will just jettison it, because that is what you tuned your body to handle, and your liver, kidneys and bloodstream will keep your blood properly balanced and flowing, and will give you the energy you need for 24 hours. Mainly they will keep your brain in charge – because, after all, it's all in your head," he sums up.