Anecdotal but I have experienced body ache from drinking diet soda with aspartame. I drank regular soda when younger but switched over to watch my weight as I aged. A year on during a more sleep deprived week I went heavy on the caffeinated diet soda and ended up with all muscles feeling like I had done some major exercising. Thinking back, I had been experiencing regular aches. I stopped for a week, felt better. Tested again by going heavy for a week and the aches returned. Tried regular soda and no aches. I just stopped soda all together at that point. I check labels now and avoid anything with aspartame in it.