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TL;DR: At what percent (if any) will alcohol dehydrate you more/faster than drinking nothing?

Let's contrive a situation for dramatic effect...

A human goes out on a boat for a nice sail in the sea. But oh, the sea was angry that day, my friends. The weather turns, and the sailboat is tossed asunder. Luckily, our survivor grabs hold of some debris and is washed onto a deserted island.

Lo and behold, the debris that floated with the survivor to the island is a cooler, and it is filled with beer! There are no other food or water sources on the island. What should our survivor do in regards to the beer to stay alive for as long as possible?

The crux of the situation and my question: will drinking the beer help hydrate the human, keeping them alive longer? Or would the effect of the alcohol as a diuretic actually dehydrate them, causing an earlier demise?

Details and follow up questions: Let's assume this is an average beer ~4% alcohol. However, I know there must be a breaking point. Some kombucha or ginger beer with .5% alcohol should surely be imbibed. But should this beer still be drunk? What if instead it was a 7% IPA? Or a 14% quadruple IPA like I have in my fridge? What about wine, whiskey, or gin?

How would the situation change for a caffeinated beverage like coffee? Or what if the cooler was filled with energy drinks?

I look forward to your answers!

EDIT: The linked question, while similar, does not answer my question. It links to one 1996 study that talks about the effect of alcohol on rehydration, but not the specifics of yes, probably ok to drink at about this percent ABV, and no don't drink at above this percent. It also doesn't discuss rate of intake, changes based on body weight, etc. which are all things I would surmise have an impact on this. I understand there isn't going to be a hard and fast STOP percent level, but I would like to understand more about the underlying mechanisms and factors that change things.

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    $\begingroup$ This is way too many questions. Focus on one or two beverages, please, or just alcohol, plain and simple. $\endgroup$
    – anongoodnurse
    Sep 13, 2015 at 0:00
  • $\begingroup$ There is one main question, at what percent alcohol is drinking nothing better than drinking the alcohol for survival. A possible follow up would expand this to caffeine. $\endgroup$
    – jdf
    Sep 13, 2015 at 3:22
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    $\begingroup$ If you read The Ghost Map, you will find that the people who survived a particular cholera epidemic that erupted around them in London, were workers in a brewery who were paid in part with the fruits of their labor, and drank beer and not the water from the local pump. $\endgroup$
    – AMR
    Sep 13, 2015 at 9:54
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    $\begingroup$ Let's hope the beer is chilled ;) $\endgroup$
    – WYSIWYG
    Sep 13, 2015 at 10:19

1 Answer 1

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There is quite a lot of misunderstanding about alcohol (and caffeine) as a diuretic. It's not nearly as cut and dry as you're presenting.

There is no answer to your question. Sodium and water are very tightly regulated, and a lot has to go wrong before they fail. If alcohol could easily derail water regulation, there would be far, far fewer alcoholics in the world.

Alcohol is primarily a toxin, not primarily a diuretic. The diuretic effect of alcohol depends partly on your hydration status. If you're fully hydrated, you'll produce slightly more urine on drinking an alcoholic (>2%) beverage than when you drink water. If you're dehydrated, your body will conserve the water more. The more alcohol in the drink, the less value it has as a rehydrating solution.

You won't find good studies because it's not a scenario truly worth studying. The toxic effects of alcohol are already known and bad enough. It would be unkind to conduct a study where higher concentrations of alcohol were the sole fluid available and length of survival on animals, let alone humans.

N.B. There have been lots of studies with acute alcohol intoxication and diuresis because that is a scenario that occurs, and which can be mitigated.

Effects of a moderate intake of beer on markers of hydration after exercise in the heat: a crossover study
Hydration Status and the Diuretic Action of a Small Dose of Alcohol

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    $\begingroup$ @WYSIWYG Alcohol is most definitely a toxin. Your assertion is absurd. $\endgroup$
    – anongoodnurse
    Sep 14, 2015 at 15:33
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    $\begingroup$ @WYSIWYG - by your logic, tetrodotoxin (made naturally by puffer fish), though it does get someone high, is not toxic. Enough. $\endgroup$
    – anongoodnurse
    Sep 14, 2015 at 19:56
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    $\begingroup$ Please refrain from making unprofessional expressions. If I do not understand what you are saying then I have the right to ask. Alcohol is an end product of fermentation and is not a product specially synthesized to cause harm to other species. It is like lactic acid (which can also cause metabolic acidosis at high concentration). Comparing TTX with alcohol is too far fetched. $\endgroup$
    – WYSIWYG
    Sep 15, 2015 at 4:37
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    $\begingroup$ @WYSIWYG- as I said, I'm done with this. Surely you can look it up yourself. You didn't so much ask a question as make an absurd statement. $\endgroup$
    – anongoodnurse
    Sep 15, 2015 at 4:42
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    $\begingroup$ I can look it up. But being a member of the community I have the right to ask for a referenced answer. Your claim can mislead others. And I do not really understand the "absurdity" in my comment. Would you please care to enlighten me? $\endgroup$
    – WYSIWYG
    Sep 15, 2015 at 4:46

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