I had diet coke throughout my time on the Cambridge and it didn't affect my losses at all, apparently the cotric acid in it affects some people and not others. I also allowed myself a treat once a week, but only some prawns or chicken and again it didn't affect my losses at all.
I no longer do Cambridge as I have IBS and it was affecting it badly, but for me if looking forward to a few prawns and a diet coke made me stick to it better, I was up for that- better than fish&chips and a vodka eh?
Take Care
Stacie x