DISCLAIMER: I am not a Doctor - just a computer nerd!
I have heard both sides of the argument for a lot of years. I think we all have. One says diet soda will kill you. One says prove it. Blah, blah, blah.... I decided to do a little personal test with so many people's drink of choice. In fairness I did not just use diet coke - I drank several brands that were all diet. For week one I drank diet sodas as normal. "Normal" for me is between 2-3 per day. For week two I did not drink any diet soda - mainly water, but one daily cup of coffee and powerade during my long training run.
Results for me were staggering.
Drank my sodas as normal. Did about 18 miles on Saturday that felt normal.
By the end of the first day I was jonesing for a soda. Not really shaking with the sweats, but I just craved the taste. I noticed my four mile run the next day felt a little different. Almost like everything was clicking better if that makes sense. Anyway, I went without soda for the rest of the week without much effort. I don't think I am as hooked on the bubbly stuff as I originally thought. My long run last week was at least 25% easier at the same distance of around 18 miles. Now I could have just been having one of those great days where it comes easy. Time will tell.
At this point I am walking away from diet sodas all together. I have not really come across hard core proof stating they are awful for you, but I feel that they do hold me back on the long runs.
So just like that....Goodbye Sodas.