Why does sodium-heavy liquids like pickle juice, chicken noodle soup, or saline hydrate you better than regular water when you’re dehydrated, but salt water dehydrates you?
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**ELI5:** Your body needs sodium (and potassium) to hydrate your cells. If you are too low or too high on either of these, you cannot properly hydrate. Period. Generally when you’re dehydrated, you’re low on sodium as well because our sweat contains a lot of sodium. So these sodium rich liquids help because they enable your body to absorb more water. Generally, not always. Saltwater, on the other hand, contains TOO MUCH salt. If you drink saltwater you suddenly have the opposite problem. You have TOO MUCH sodium and your body can once again no longer properly hydrate.
**ELI’ve taken chemistry:** Your body’s cells use something called a sodium potassium pump to regulate the amount of water in your cells. The way this works is that enzymes in your cells will pump an unequal amount of things either inside your cell or outside. I THINK the ratio is like 2-3 or something. So it’ll pump 3 sodiums in your cell but only 2 potassiums out, therefore increasing the charge inside the cell (because both sodium and potassium have a +1 charge). What this means is that your body regulates the amount of sodium and potassium on the inside and outside of your cells. By doing this, your body uses osmosis to hydrate your cells. (Osmosis means that water will ALWAYS flow from an area of low concentration to an area of higher concentration. Don’t believe me? Fill two glasses with tap water. Connect them via a wet paper towel. Put a bunch of salt in one and leave it sit for an hour, watch what happens.) So, if your cells are dehydrated, they’ll pump more charge INSIDE the cell, so that the concentration of ions INSIDE the cell is higher than the concentration outside, so that water, via osmosis, will flow INTO the cell. Therefore you NEED sodium to hydrate. If you are too low on sodium your body cannot physically hydrate. Visa versa for a cell that’s too hydrated.
So, because your body uses this sodium potassium pump in your cell walls, it NEEDS sodium and potassium to properly function. Furthermore, it NEEDS sodium and potassium in a relatively consistent ratio. Anything that’s not close to this ratio is bad. Whether one is too low or too high. Too low sodium is bad. Too high sodium is bad. Too low potassium is bad, too high potassium is bad. (Some of those four are worse than the others though.)
GENERALLY when a human is very, very dehydrated, they’re low on sodium and low on liquids. Drinking a sodium rich drink helps with this. We lose a lot more Na in our sweat than we lose K, so it needs to be replenished more. This is why we often do 1/2 water and 1/2 Gatorade because MOST OF THE TIME, we’re not seriously dehydrated, and we need more liquid than sodium.
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