Are you claiming that agreeing with friends to experiment with diets does not fall under that definition? If so, which part do you think it doesn't meet? If you

Are you claiming that agreeing with friends to experiment with diets does not fall under that definition? If so, which part do you think it doesn't meet? If you read "physical or psychological intervention by the researcher upon the body of the subject" in such a way that a friend telling another friend to follow a given diet doesn't qualify then most medical research would be exempt too - researchers generally give subjects medication and tell them to take it rather than physically pushing it down their throat.