I lost over 2 stone a few years back and have managed to keep it off, I just reduced my portion sizes and stopped snacking between meals, so ate less calories than I was burning,
I think at the time I was eating around 130g of carbs a day, it was also around this time that I did the DAFNE course, getting to grips with injecting the right amount of insulin means fewer hypo's which in turn leads to fewer calories consumed.
I also got some helpful advice from the dietitian at my hospital clinic.