About five years ago I gave up caffeine and aspartame for almost a year. I have fibromyalgia and some people find caffeine and aspartame to worsen their symptoms. I didn't notice any drastic improvement, but figured it was a good idea anyway. When my fatigue was getting worse, my doctors prescribed Provigil, but advised me to choose caffeine before prescription meds. I'm trying to drink more tea, because it's a more natural source of caffeine, but my caffeine delivery method of choice is still diet soda.
I think that sometimes we have to pick our battles. My goal is to eat cleaner, but progress over perfection works best for me. Everything in moderation, even moderation.