Every doctor is different in how they want their pre-op diet to go. My doctor required my husband and I to have 2 low carb protein shakes, one for breakfast and lunch, and then dinner consisted of 4-6 oz. of a lean meat and as many green veggies as we wanted. As for the headache, it sounds like you are having sugar issues. I would call your doctor's office and find out of it is possible to have a small 4 oz. of orange juice in the middle of the day or something to keep you from having the headache issues. I myself am hypoglycemic, and that is the only way I can be on a diet that is sugar restrictive. I was banded on Feb 16th, it is rough...but stick it out - I am sure all will be just fine!