It is undoubtedly true that what you eat will to a large extent determine you constitution, however our reality is a perceived reality, coloured by the glasses we wear.
Objective reality simply does not exist.
Add to this that perception is all powerful and that most people will not be able to separate perception from reality. When the perception is that a certain part of town is unsafe to walk at night, regardless what police reports say and statistics indicating otherwise, people will feel insecure and afraid to go there.
Scientists too, in facing out-of-the-ordinary truths have a hard time acknowledging what may be staring them in the face..
Concurrent events do not necessarily have to be causally related and yet too often scientists fall into that very trap. Sometimes to get quick and easy access to funding for their projects, sometimes because it happens to confirm their ideas or hypotheses. However in all these cases it is without fail due to bad science affected by preconceived notion of perceived reality.
The big question of course will always be: Are we conciously or unconciously deluding ourselves and to what extent are we reshaping reality into what we believe it to be or fear it to be. Are we the creators of our worst fears come true?
Is  the placebo effect substituting a reality for a believed reality?It does happen in a myriad of circumstances, and under all sorts of conditions, completely independent of social or cultural variables. However the placebo effect is nothing more, nothing less than a strong impetus for a belief that is strong enough to affect the course of a disease. In other words, how and what we believe to be true affects something physical. Mind over matter is a reality we often fail to acknowledge as having a scientific ground for existence.

In this I also fully agree with the precepts of the -now defunct - group: Refus Global
and one of my favourite artists Paul Borduas :

I believe that we are run by our fears :

- fear of facing prejudice
--fear of public opinion
--fear of persecutions
--fear of general disapproval;
- fear of being alone, without the God and the society which isolate you anyway;
- fear of oneself
--fear of one's brother
--fear of poverty;
- fear of the established order; 
- fear of new relationships;
- fear of the superrational;
- fear of necessities;
- fear of floodgates opening on one's faith in man -- on the society of the future;
- fear of forces able to release transforming love;
-.......... . blue fear -- red fear -- white fear;

Paul-Emile Borduas : Refus Global
You are Not what You eat..
You are what You believe !