There are so many problems with eating fast "food" that I can't get into all the details here. In fact, its not really food... its an edible food product, but has little true nutritional value and no life. Same with processed food, but it wasn't in this study:

"Mice fed junk food for nine months showed signs of developing the abnormal brain tangles strongly associated with Alzheimer's disease"
source: http://www.reuters.com/article/scienceNews/idUSTRE4AR48G20081128

Its amazing that people still continue to eat this stuff... but its remarkably cheap and (of course) fast. Convenience seems to trump health... hmmm... seems like a remarkably familiar pattern with a clear outcome.

Seriously though - eating some fast food from time to time isn't going to kill you (even if 95% of it is narsty... yes, I meant narsty). But, just know that eating it regularly (more than once a week) for years is only going to increase your risks for everything bad.

Of course, its easy to say you don't care, but think about the long term costs... health care isn't getting cheaper, so that "dollar value" burger might actually cost 2-3 times what you are paying (if not more).