b) even diet soda can cause insulin spikes, causing rats and calves to gain more weight on the same # of calories as rats/calves not consuming diet soda
There are links off the wikipedia article: http://en.wikipedia.org/wiki/Diet_soda
There have also been lots of books written about the insulin response and weight gain, all citing studies, all pointing out that insulin resistance/syndrome x play roles in making some people fatter even if they do not overeat. Gary Taubes' is especially good.
I don't know why nerds seem to want to persist in believing that a calorie is a calorie is a calorie, despite all the evidence.
In my mind, it's like a nasty twist on "tough love" -- people want to believe it because they want to believe that fat people are bad and weak, and therefore deserve what they get. By taking a hard line approach, they can feel... virtuous.
But the body is extremely complex, and a tightly-coupled system at that, with so many variables that it is vanishingly unlikely that we can categorically say that there is one simple, clear, clean fact that rules it all.