Insulin does not make you fat. Let's make that very clear. Having a cr*ppy diet makes you fat. Furthermore, not taking insulin (if you need it) does not exempt you from having a poor diet...it will just kill you (eventually). I usually try to avoid scare tactics, but this is a very important subject.
Gaining weight is pretty simple: eat more calories than you burn.
Gaining HEALTHY weight is a lot harder. In my opinion, it's not about eating everything in sight, but rather eating often and eating consistently. In my experience, you can gain weight on a low carb diet or you can add lower GI carbs into the equation. Excess protein and low GI foods seem to have the same effect on me in the sense that they help me gain healthy (muscle) mass, but not at the expense of managing my diabetes.
I've recently added a fair amount of carbs back into my diet up to about 150-200g from <50g previously. Why? Because part of learning what works is also figuring out what DOESN'T work. Plus, I don't believe that a low-carb diet is the ONLY approach for a diabetic (although it's certainly a strong consideration for most).
Sorry for going off on a tangent, let's get back on track: the answer is simple...if you want to gain weight, you need to be eating from the time you wake up until the time you go to bed. Again, that doesn't mean stuff your face with junk food.
It means eating eggs, bacon, and maybe a small piece of toast in the morning.
2 hours later, a handful of almonds or other nuts
2 hrs later another small snack
A chicken salad for lunch
Another snack in the afternoon
Another meat for dinner, green veggies, and perhaps some sweet potatoes
Drinking a glass of milk, or a scoop of casein protein (depending on what your blood sugar can handle)
I understand that won't work for everyone, but that's why you customize the plan to what works for you. Nothing on that list is terribly difficult to manage in terms of blood sugar, yet I can easily get it to exceed 3500 calories without much effort.
