One diet coke per day is maybe OK, but 8? That may be too much. The equivalent of that amount made mice cower in a corner in fear. Take a look at the pictures .. after 12 weeks this metric of anxiety in mice showed strong effects of aspartame, which is the sweetener in most "diet" anything.
I found this to be solid neuroscience published last month in PNAS, plus some weird epigenetic inheritance of anxiety to the offspring. Wild.
