I also had to do the 6 month thing and the cardiac etc. My pre-op was 3 weeks long and finally my surgery is the Wendesday. You can make it through the pre-op. Atkins is good but be careful, the price varies alot. In Connecticut I paid as much as $8.99 for 4 cans and as low as $5.49. That is the only protein shake I tried
I have also eaten alot of chicken and beef broth. I found onion soup with the onions strained out to be good. Also, my doc allowed low fat yogurt and string cheese and cottage cheese.
Be careful with your glucose. I started to go hypoglycemic the first week, so I had yogurt,skim milk or apple juice every few hours to keep the glucose up.
Good Luck