Having watched Dr MM on YouTube this week my husband and I have decided to try the 5:2 however I am quite terrified by the prospect of just 500 kcals! I am overweight by a stone or so, but I workout twice a week and swim 3k a week and am in training for some ultra hikes over the summer - would it be completely against sensibility to be on 800 for the fast days at least to start? Or should I just suck it up?!