"Natural flavors" is in seltzer water with 0 sugar. It is also advertised to have "no artificial sweeteners", which I realize might be bending the truth somehow, but I'm pretty sure food and drink companies can't outright lie about that stuff. From what I've gathered it doesn't affect insulin levels like the artificial sweeteners from diet soda does, but I also can't figure out what it actually is.

Side-note: sugar after a workout is the best time for sugar. You want to replenish muscle-glycogen as soon as possible and sugar is a fast track to that. Obviously you should opt for fruit over a Gatorade or sweets though.