What exactly is the pre opt diet? What does it consist of?

I was told the pre-op diet was to get me in the best health before surgery and to shrink my liver. My pre-op diet started 3 weeks before my surgery date. I could have 3 meals that were either a protein drink or bar and 1 real meal that was 6oz of lean meat and 1 cup of veggies. The drinks and bars had to be under 200 calories, 7 g fat, 7 g carb and over 15 g of protein. My nutritionist gave me a list of them that I could get online and certain stores but I did find almost everything in my local grocery store. I lost 12 lbs doing the pre-op diet and the doctor said my liver looked great lol. Good luck to you!