I am looking for a word to describe people who hate, or are phobic of fat people. Something like "fatophobic".

Hello, Pepa. Welcome aBoard!

I found the term ‘fat-phobic’ on the Psychology Today website. Here is a link to the article: http:// http://cms.psychologytoday.com/articles/pto-20010301-000037.html .

The term seems to be fairly prevalent on the web, but that’s no indication of the term’s validity. Unfortunately, I couldn’t find an official list of psychological phobias anywhere that listed the specific phobia you mentioned.

Well I don't know if it is the "official" word for it or not, but "steatophobic" might fit the bill.

See also:

http://www.m-w.com/cgi-bin/dictionary?va=steatopygic