I'm interested in the whole insulin makes (T2) diabetics fat thing I keep hearing. For T1s it's obviously a bit different - by definition if you're dead you can't put on weight, so it's a moot point, though the points below would also apply before the being-dead bit happens.
For those who are eating the same quantity of food before/after starting to take insulin, presumably the root cause of any resultant weight gain is that rather than glucose being lost overboard in their urine, it's being stored (in adipose tissue) due to the insulin? Therefore if they were not diabetic they would have the same weight gain. On the positive side at least they won't suffer from complications caused by long duration high BG.
I could also see that perhaps when taking insulin and having lower BG levels this may result in increased hunger (if constantly low), or at least normal levels of hunger (that was previously diminished due to high BG levels.) Normal is obviously different in different people, but again it seems like this is more that someone is going back to normal rather than insulin causing the problem.
In both of the above cases I don't think insulin can be blamed, rather BG level itself (and potentially incorrect use of insulin if you're running low).
There is also a (I think small) effect of increased insulin concentration in peripheral tissues causing adipose tissue to increase in size, which I have read about as a justification for the "insulin makes you fat" theory. Does anyone know off-hand if injections require more insulin than would be produced by the pancreas, I assume it should be a similar amount, which would mean that any direct effects would be localised to the injection site. If this is true, I'm not sure how big an effect it actually is as I've been injecting for more than 35 years and while I weigh more than I did when I was 7, I'm lean, and my injection sites are not fatty.