Fat does not get good blood flow. You wont find much of any veins to inject into while doing a sub-q injection. None the less, I would always recommend consuming your carbs before you take your shot and have them in your blood. That way, if something were to go awry with your shot, you'd have carbs in your blood and be ok. Good question though. Insulin can be a dangerous so any questions you have about it are certainly worth asking!