At first, I did not gain weight because I think it actually cut down my insulin needs because the pump keeps track of the active insulin on board in our system already- so I found myself giving less insulin than I thought I needed.
What I am trying to say is- let's say my carb ratio is 1 to 10- and I have a 40 gram meal- AND my bloodsugar is 100 (right!!-it does happen!) I would manually inject 4 units.
Well, if I were to put in bloodsugar 100 and 40 carbs it might actually give me less than 4 units depending on when I last bolused insulin and the rate at which I have active insulin programmed into my pump. Also, of course it would adjust more or less too depending on my premeal blood sugar that was other than 100- like if it was 80 it would give less to, plus less the active insulin working. I used to do that also in my head and am really good at math, but the pump is just way more precise at calculating the active insulin part- I really used to only acount for my carb ratio and insulin sensitivity ratio in my head was not able to account for the active insulin already in my system- hope that makes sense!
I am sorry if you already know this info and you've heard it before- anyway, just explaining why I think I didn't gain weight.
But now after years of wearing it and it is sooooo much easier to eat more and snack more, I sometimes think, if I was on shots I wouldn't eat sooo much- but I think I am deceiving myself- so since then, I have had some weight gain, but it I think it really has to do with eating behaviour and age- I don't think I can blame the pump for eating those extra potato chips I shouldn't have had!
This is just my experience. But I would like to hear from others too because if there is something I don't know, and I found out going off the pump would instantly help me lose the 20 lbs that I so want to lose, I would take it off in a heartbeat! I am vain.