Is it possible?

 Is it possible that using protein shakes to get in all of your protein instead of dense forms of protein like lean meats can cause one to gain weight? I'm just curious and want to know how protein powders compare to dense protein regarding weight gain or loss.

A lot depends on the type of surgery you have

With the RNY one of the key mantras for any meal is "protein forward" or "protein first"

if you get ALL your protein from shakes, this leaves room for other types of food than protein, and pretty much ALL other foods out there other than protein are less dense.... leaving your pouch quicker than a pouch that has been filled up with dense proteins and topped off with "lesser" sources of food.

So yeah, I could see it as very easy to start regaining all your weight if you do ALL your protein in shakes and have no self control when eating (ie, you get hungry sooner..... if you eat every time that happens you'll gain)

me.....I like to get 50 to 70 g in protein shakes, but I ALSO try to make my meals "protein forward" ...... I pretty much don't count protein grams in excess as a source of weight gain, and I don't worry about fat and make an effort to get MORE fat in daily..... but I try to watch anything that is a carb because those are going to be the devil that makes me gain

The only way protein shakes will cause you to gain weight is if you either consume a ridiculous amount (resulting in entirely too many calories) or they are full of sugar. Otherwise, the only difference I can think of is that the shakes may not keep you feeling full as long as dense protein, which may lead to eat again sooner, which could result in increased total daily consumption.