I've known a few women who have had bypass surgery. One of them lost an amazing amount of weight and she's like a size 6/8 now. It's been maybe 13.5 months since she had it done so I can't really speak to her habits.
Another friend of mine had it done many years ago. Sadly she has pretty much undone all the work since she has stretched out her stomach to the point where she can (while in pain) eat or drink large amounts of food or alcohol. I don't think she's as large as she was (I didn't know her then), but she's definitely gone back to the overweight/obese side of the scale.
A third friend had it done I think about 6 years ago. She continues to maintain a decent weight, but from what I understand it is a struggle.
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We do follow a very similar diet to what all of these women followed after their surgeries. The difference is that when they came out of surgery and were eventually healed they had no stomach. They didn't have an empty void (of stomach) waiting to be filled (with food). We do. So we have to learn restraint and portion control without the additional "help" they get from the surgery. I'm glad I never went that route. I'm not particularly happy about my ability to eat a whole pizza, but I'm glad I don't have to worry about malabsorption of my nutrients due to the surgery and all of the complications that could occur.
Now I've overeaten to the point where I was in pain, but from what I have witnessed it can't even begin to compare to the pain I've seen my friends mentioned above experience.
One of them can't even vomit successfully (this is not in connection with overeating but with food poisoning, illness, and a couple times she got way too drunk). I guess because everything passes out of the pouch so quickly that if you're ill you are sol. no pukey for you. that would stink
sometimes you just need to to feel better.