How long can one live on Guinness and spinach

I think you’re right. Doesn’t alcohol inhibit vaospressin in the body?
IIRC, vasopressin is an anti-diuretic hormone which regulates your kidney and stops you peeing everything out.
So if alcohol inhibits something which stops you peeing, you surely have to pee more than if you were drinking the same volume of a different liquid with no alcohol in it? Therefore, you’d have to end up dehydrated, if the benchmark for hydration is a person who isn’t drinking alcohol and so has optimum vasopressin function.