Not sure about studies, seems more like a useful cultural thing, one of those traditions whose internal justifications have nothing to do with the reason they are useful:
In this case it is probably about having a balanced diet with enough calories, vitamins, minerals etc. It is probably far from optimal, but a good-enough simple advice an average human can follow.
Not sure about studies, seems more like a useful cultural thing, one of those traditions whose internal justifications have nothing to do with the reason they are useful:
https://slatestarcodex.com/2019/06/04/book-review-the-secret-of-our-success/
In this case it is probably about having a balanced diet with enough calories, vitamins, minerals etc. It is probably far from optimal, but a good-enough simple advice an average human can follow.