Not buying the low income excuse, when I was on low income I would have loved to have enough money to be able to afford fast food every day. If I had been doing that I wouldn't have been able to afford rent.
I don't go to mcdonalds but just looked up their prices. A single "big arch" (wtf is that? first thing on the menu) for £10, about the same as a weeks worth of food with the sort of things I was getting poverty shopping.