"The late Wally Sampson characterized FM as 'claims cloaked in the language of science, but with the distinguishing characteristics of sectarianism—pluralities of approaches to illness, absence of evidence or efficacy, a unifying concept of illness as a body out of sync with Nature (with the capital N), undecipherable babble and descriptive word salad.'"

http://www.skeptic.com/reading_room/why-functional-medicine-is-bogus/