Sorry man, that's not how it works. And if he's eating refined sugars, flour, twinkies and junk, it's excess fat he has going for him, not water.
Furthermore, those guys are doing a massive amount of exercise pretty much on a daily. Not sure exactly how much water one sheds per game, but for Alzner to have so much water retention for you, someone who has never seen him in person, to notice, he'd have to be retaining so much of it. Really doesn't make much sense.
I think it's a bit silly to look at a professional athlete's face and say "omg...outta shape". You really don't have an idea.
Phil Kessel always looks pudgy. He still flies on the ice, and performs even better in the POs.
The problem with Alzer has nothing to do with his physical condition. He was never a fast, mobile, smart Dman. He was your classic shutdown D. Those guys are no longer needed in this league. A few here and there that can be useful, otherwise, they constantly get exposed and need to be carried.
So if his partner is Petry, and they're facing top opponents, no level of fitness will improve his game.