The amount of weight lost varies depending on the person, as Retired Seabee said. The more weight you're carrying prior to the surgery, generally, the more weight you will lose. If you think about it, it makes sense. You have to eat a certain amount of calories to maintain the weight you were prior to surgery. During recovery you're eating many less calories, so you lose weight.
Once you start eating the same amount and types of foods you ate prior to your surgery, you'll gain your weight back. If you don't want to gain it back, then by all means don't go back to eating the same number of calories again. If weight loss is a concern and you've become underweight, you can easily compensate for smaller meals by eating more of them and adding more high-calorie foods.
Nissen Fundoplication 2/09
"Whatever you fight, you strengthen, and what you resist, persists.”
“Worry pretends to be necessary but serves no useful purpose”
“Accept - then act. Whatever the present moment contains, accept it as if you had chosen it. Always work with it, not against it.”