I am 12 days from my surgery for gastric bypass and my nutritionist gave me a 1000 calorie balanced whole foods diet with high protein and low carbs. I chose to have a protein shake with lunch but have a cup of green beans, 1/3 c quinoa, and 3 oz of grapes. I have 5 small meals a day and I don't have to do a liquid diet until the day before surgery. I've already lost 7 lbs in 4 days doing this. And I'm not hungry. I think the big issue is getting in your protein and cutting out fat, carbs, and sugar. Each doctor is different though.