When I went low-carb for a short time I too found I would need a fair amount of insulin for no carb meals, I think it's trial and error on how much insulin you will need following a low-carb diet and only by testing will you know the answer.
As protein and fat break down much slower than carbs I found split doses of insulin was the only way to keep my bg levels within target, injecting a small amount up front with my meal and again 2-3 hours after would avoid prevent a preprandial bg rise before I next ate, hopefully some more experienced members will be along soon to advise you.