I was going to say that I don’t think being isotonic had any relation to how refreshing a drink is except in terms of taste. But then after thinking about it, salt does affect the rate of water excretion into the urine and water retention in blood. And because of this phenomenon they always recommend low salt diets for people with high blood pressure. So I guess in a way, a low salt diet would be considered more “isotonic.” But solid food will inherently not be isotonic due to containing more carbs and amino acids than water.