I'd take the idea that there are actually people who kill for human fat with a massive block of salt. There has been news stories about this sort of thing for years and when serious journalists get involved they can find very little real evidence.
It's an interesting myth though. My wife tells me that when she was naughty her grandmother told her that she better be good or the pishtaco would come for her. Her idea at the time was that it was a sort of bogeyman figure that would get you in the night.http://en.wikipedia.org/wiki/Pishtaco
And this article talks about pishtacos wearing felt hats, boots and being white which sort of describes my appearance in Andahuaylas when I was looking at those drainage ditches that day.http://www.jstor.org/pss/539781
After I left the village a colleague (Peruvian) went back. She got talking to an old women who asked about me and she said I was fine. The old lady said "it's not true what people are saying, is it? That he's a pishtaco."
I got talking to my Peruvian colleagues and was amazed that quite a few of them (university educated) beleived in them. One of them (who was a very white Peruvian and tall) actually told me his deceased grandfather had actually been one!
There's great horror movie material here. I don't know why they don't make a vampire like flick about them.