I am on day 7 of my pre-op diet. 5 Opti-Fast shakes per day. Thats it. Days 2 and 3 were the worst for me! I was miserable...not hungry.....massive headaches and absolutely no energy to speak of. Now I feel great. i have lost 10.5 lbs however, I am still struggling mentally with the food. It is hard for me to be alone...thats when the food calls me from the pantry. But I just keep thinking it is ALL worth it in the end!!!! You can do it!!!