Buenos días Sarah, 

I think if the speaker was describing an holostic diet more generally i.e. advising others to follow such a diet, then the possessive pronoun wouldn't be used: "una dieta holística es muy sana para el cuerpo... y la mente. However in this instance the speaker is describing personally the benefits for himself; it's a personal account of the benefits... hence: para mi cuerpo...

Just my opinion though.  Inma or Silvia will clarify if I'm right or not on this. :)