A very important difference is that you can't drink water during a Ramadan fast. Regardless of what you're doing with your food, deliberately dehydrating yourself is pretty much never justified.
After realizing that water is a byproduct of catabolism, I'm willing to entertain the idea that it is beneficial.
> After realizing that water is a byproduct of catabolism, I'm willing to entertain the idea that it is beneficial.
The two parts of this sentence aren't connected by logic.
The body produces water as a byproduct of ATP (energy) metabolism. During a fast, fat and other tissues are broken down by catabolic reactions to accomplish this. Knowing this, I am willing to entertain the idea that abstaining from water for a period of time can be beneficial, or perhaps I should say at least not harmful, because there are mechanisms in the body that synthesize water. Obviously, a sufficiently long period of time without water would be harmful.
I haven't done the math to figure out how much water this is, and so I do not know how sufficient it is to keep minimally hydrated during a water-fast. I'm just saying that the thought of abstaining from water during a fast isn't necessarily as dangerous as it sounds, because your body can and does produce it's own water as a by-product of energy metabolism.
From https://en.wikipedia.org/wiki/Metabolic_water
> Humans obtain only about 8-10% of their water needs through metabolic water production
A religious obligation won't count as justification?