After surgery, how common is it that if you overeat a few times, it causes the stomach to expand and return to the normal size?

You do not stay which type of surgery you are referring to but after sleeve it is normal that the stomach will stretch a bit again but it will still be smaller than before the surgery.

The stomach is a muscle and adapts to how it is used so if you regularly and continually eat large amounts it will retain the size needed for those expected meals. It is how a lot of us (well me anyway) got to be the size we were that surgery was the best option.

Not sure what you class by overeating as different to everyone (like a handful of nuts vs a packet of biscuits) or how often you mean "a few" but in the immediate weeks and months after the surgery you would not be able to eat much at all and then after some time you would be eating what will become the new normal size meals. If you just eat a bit much a few times over a long period of time it should not be an issue but you may feel uncomfortable those times.

The time pre-op and the phases of food reintroduction post-op is about doing the work mentally also to understand how, what, why and when you eat. It can be hard but it will then help you use your new tool (smaller stomach) to go forward and not stress about things like an extra bite of something delicious every now and then.

If you are having a gastric bypass, you are left with a little pouch the size of an egg. It doesn't bulge any longer and you no longer have the sphincter muscle at the bottom of the stomach to keep food in. Food flows right through it, and thus, it doesn't stretch out at all. If you eat too much, you will feel it, especially since you are not to drink before or after meals by 30 minutes, to give the food a chance to hang out for a little while. Once you start drinking you are pushing the food down into the intestines. There are certain rules to follow regarding food and what kind, etc.

Stretching your tummy out again is really just a false scare tactic that anti surgery people spread. To stretch your tummy again you would have to eat very large meals regularly for a long time. You’d have to be committed to doing this. You’d have to eat through the discomfort of your restriction. You’d likely vomit to bring up the excess food you’ve eaten at those large meals. Would you want to do this?

The stomach muscle will soften in the months after surgery which allows you to eat a little more as the months pass than you can immediately after surgery but the little more gets you to a point your eating around an acceptable & recommended portion size and allows you to get the nutrients in you need. For example after surgery I could only eat about 1/4 - 1/3 of a cup of food. I’m 6 years post surgery & my meal fits on a side plate now so about 3ozs cooked meat and a cup of vegetables to give you an idea.