perhaps we're the same subtype, then. i also get really upset when people criticize my diet, appearance, etc. i get less upset when i work on as a function and attempt to be healthy, but then i'm more like an ISTp or something and don't attempt to predict anything (which is possibly a much better strategy when hanging out with ISFps/ESFjs.) so perhaps it's like something i know i totally avoid and thus try to work on a bit. generally when the topic comes up i just a) shut down and sort of avoid it or b) get pissy and hypersensitive. the point is that i can relate to that quite well. i believe expat has called the "charmer" function but this hasn't always been the case in my experiences with types. more or less with ISFps and such i find that they more or less expect you to be highly agreeable and happy and if you're not, well then "something's wrong with you."

at any rate, i don't really have an answer to your question because i've often wondered the same thing. i think i go back and forth between feeling like one is stronger than the other though.