Hiya! So your surgeon/ bariatric nutritionist will probably give you a diet plan that they want you to follow, mine may be different. Mine had me do 4 protein shakes a day ( I only had 3 choices of shake too), all other fluids were separate. Of course you could mix your shake with crystal light or skim/ unsweetened almond milk though as long as it's approved. Some shakes like bariatricfusion have fiber in them (and tons of vitamins and minerals too), so he said there's no need to add unless I feel constipated. However other shakes do not, so to each drink to add 5g of fiber to each shake. I also had 1/2 cup of un-starchy veggies a day I was allowed (i added them to broth). If it is a pure liquid diet there is unflavored fiber powder you can use, food could keep your liver from shrinking, but of course you can ask your doc! My liquid diet has been going great I haven't cheated once and on day 4 I am no longer hungry since I pump myself full of fluids and my protein drinks.