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Salt shaker. Photo: <a href="http://www.flickr.com/photos/50388630@N00/2081320295/">pboyd04</a>, Creative Commons, some rights reserved
Salt shaker. Photo: pboyd04, Creative Commons, some rights reserved

Natural Selections: Why we need salt

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Besides making our food taste better, sodium chloride (salt) is necessary for our bodies to function. Martha Foley and Dr. Curt Stager whet their appetites on the science of salt.

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Martha Foley: So we’re always talking about, you need this in your diet; you need that in your diet. You need this, you need that--mineral… vitamin… whatever. My question is why? What does that stuff do? And let’s talk about salt. Because we were talking about salt before and we talked all about salt, but we didn’t say why we need salt. I mean, what does it actually do in there?

Dr. Curt Stager: Yeah, it’s a really interesting time where people again can look down on the level of things you can’t see. So before, we all knew you wanted salt, you crave it, you can taste it. Other animals are using it. Butterflies are licking it out of puddles.

MF: It’s not just because it makes something taste better.

CS: Right, that’s half the story.

MF: That’s the marketing part right there.

CS: The marketing part, okay. Now, the evolutionary big picture is that it tastes good because you need it. You’ve got taste sensors in your mouth rewarding you for putting it into your mouth. So well, if you think about it, if you ever cry your tears are salty. Your body fluids have this in there. Your blood is salty, if you’ve ever had a cut and you licked it.

MF: We’re salty folks.

CS: We’re salty folks, and basically, animals are full of salty fluids. So that’s where your sodium is going and the chlorine that comes with it in the sodium chloride. Some other atoms are in there, too, but just focusing on the sodium story because it’s better known, there are really two uses for it. One of them is to maintain the water balance of your body. To keep you sort of inflated instead of being a dried-out mummy. You have to mix the right amount of salts in there to control osmosis, how water will be moving in and out of your tissues. You may lose it all if you don’t have some salts to anchor the water in your body. It helps hold your shape and give your cells the shape. So that’s part of the story.

MF: Really? Huh, okay, that’s one thing.

CS: But to me the juiciest part is that you use it more actively than that. Your nerves use it to function. So every thought you’ve ever had, every motion or every action you take is controlled by sodium moving in and out of your nerves. Because the signals in your brain, the signals that make your arm move or make you taste something--even, ironically, the way the nerves fire off is not electricity like in a computer or a machine. It’s the movement of little atoms, little positively charged sodiums and also potassiums--but mainly sodiums--just moving into the cell all the way down the length of that long string of the neuron. It’s the movement that is the signal. So, if you don’t have sodium in your body, your nerves don’t work.

MF: You’re done for.

CS: So you need the right balance, not only to maintain the fluids in your body and the shape of your cells, but it’s what you think, feel and move with.

MF: Does it matter about… I mean, you don’t want to eat too much salt.

CS: You don’t want to eat too much, but you don’t want to eat too little. So it is this amazing balance and you control it. Your mouth is like the portal for your body, how much is going to come in? And your taste sensors say “oh there’s a little sodium in that food, that tastes really good. I’m going to eat more of it.” But if there’s too much and it doesn’t taste good, your sensors tell you “don’t eat so much of this.” Then the rest of it, you are losing in your wastes; you’re losing it from your skin and you’re losing it from evaporating off your sweat and things like that. So it’s always coming in and always going out. You’re body is carefully regulating--not too much or not too little--making sure your nerves will work right basically.

MF: Fascinating. I’m sure there’s a story about everything we take into our bodies that is interesting like this.

CS: That’s why when you need something, it’s because it’s doing something inside of you and being a part of who you are. So, ironically, you could even say that the sodium in your body is helping you find more sodium to eat.

MF: You could say that. Thanks very much. Dr. Curt Stager of Paul Smiths College. I’m Martha Foley at St. Lawrence University.

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