| Because you really need insulin, weight gain is not going to be an issue.
When I made an experiment of trying to go back to very low carb as my only form of control a few months ago, I found I got raventously hungry as my blood sugars were higher than they are with insulin. Going back to insulin the hunger disappeared.
I think the problem with insulin leading to weight gain is mostly because it is prescribed incorrectly and people do not learn how to match it to their carb intake, so they end up having to eat to catch up to their too-high insulin doses. | 
