Even though my doctor told me I may not have to go thru a pre op diet phase... I still opted to start considering I wanted to get into the groove of losing weight. I take isopure protein shake and it's ok, I don't hate it and clearly that can't be my only meal either. I got such severe headaches on zero carb consumption, that headache sustained for 3 ????days. Thankfully the headache went away and so did my diet, will try to jump back on the wagon!