The surgery may be science, but the art of eating, post-surgery, isn't one size fits all as I have learned. I had the bypass and a hiatal hernia repair on June 6 and have been expanding my permissible diet within the general guidelines. I find that the hardest thing is the the line between full and over-doing it, particularly with new post surgery foods. I had one instance of "foamies" that caused me great discomfort- I wish I could have puked and gotten it over with; instead, I suffered gastric distress for hours, and eventually fell asleep sitting on the living room couch.
You should talk to your nutritionist - sometimes, it seems, it is the food itself; sometimes, perhaps eating too much, too quickly.
I'm finding the line between full and overfull to the point of distress to be a pretty fine one and easy to cross. The "frothing/foamies" gave me religion in the sense that I'm more careful about what I put into my gullet, how much and how quickly.
This is a significant operation that changes a lot of your physiology- the volume and nature of the food you can accept and the degree to which you can explore new food options (within the guardrails) that don't make you sick.
My take, also as a new post op patient, is that you have to take it slowly, be deliberate and work with the surgeons' staff and nutrionist to help you on your way. Nobody said it would be easy, but the rewards start to come pretty quickly. For me, just a little more than a couple months out, I have far more mobility, I'm not focused on the scale but more on my physical capabilities. I go see the surgeon for a follow up next week. My blood work looks pretty good, it has improved already.
One other thing: I can still enjoy the sensation of eating good food, but that's subordinate to my main mission to remedy the problems that necessitated the surgery--not just weight loss, but Barrett's. The bypass pretty much eliminated GERD, which was huge. The weight loss is coming a long nicely and I'm deferring to the surgeon's team for advice.