The answer to that is really a yes no one.
It is like a lot of things, yes we can eat most things but all things in moderation.
Insulin will cover, but you have to calculate for it and even then we can get it wrong espically if eating fatty slow digesting foods like curry, Chinese, pasta etc.
I think, some T1D gain weight before they are diagnosed because of the excess amount of sugar floating so the body will metabilise the stuff and store it as fat (I think thats how it works) but generally start to lose it once there on insulin and regain control of their BSL and also alter their diet.
And just to throw a spanner in the works, and no doubt upset some, I do eat anything. I survived the 70, 80 and 90's boil in the bag fish, £1 cottage pie etc. Now a days I do, with the help of Mrs K, watch what I eat simply because as I get older my metabolism is changing and my appetite is not as it was some 30+ years ago
On a side note I had a sausage casorole last night with couscous and green veg type things worked out the carbs and inject 2 units

That has to be the least amount of insulin I have EVER injected for an evening meal and stayed in the 6s all night woke with a 7.3.