your kidneys rely on osmosis ( an effect that "pulls" water form low concentration mixes to higher ones to equalise the mix strengths) to move waste materials out of the blood and into urine.
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thus, to shift a lot of salt out of the body, you need to loose a lot of water, which dehydrates you.
Xerxeskingofkings t1_jeglfm9 wrote
Reply to ELI5: How does salt seemingly hydrate you and dehydrate you at the same time. They always say you need electrolytes (salt?) for hydration, then why can’t we drink sea water? by TriCombington
short answer: Osmosis.
your kidneys rely on osmosis ( an effect that "pulls" water form low concentration mixes to higher ones to equalise the mix strengths) to move waste materials out of the blood and into urine.
​
thus, to shift a lot of salt out of the body, you need to loose a lot of water, which dehydrates you.