It may be important to note that I don't eat or drink "diet" anything. I can't stand any of the artificial sweeteners. I far prefer water to any of those options.

I also don't know if it's the fructose or the corn that's my problem. I haven't tried substituting non-corn-based high-fructose sweeteners (which would include things like honey, invert sugar syrup, and agave nectar) to see what effect they might have.