Mostly nonsense said with authority. Psychology and dietary advice really are crap sciences.
Psychology isn't all bad, since a lot more folks with severe mental illness can now go on to lead a much more normal life due to medication and coping mechanisms. Same for folks that go through trauma and have after-effects. But we are still refining this stuff, so some of it is going to be crap and there are going to be lots of pseudo-psychology fed to the uneducated masses.
Nutrition is somewhat similar. We simply don't have the knowledge to understand its complexities right now. But it isn't all crap: We understand connections between malnourishment and stunted growth, for example. Understand folic acid helps prevent birth defects and vitamin C helps prevent scurvy. To confound matters more, we have a lot of misinformation, partially due to politics and business practices. This isn't really confined to nutrition, though. Society is prone to reject new ways of thinking. Heck, the US pushed against modern "european-style" medicine back in the 1800's - they didn't think they needed science in their medicine or something like that.
- http://www.nature.com/news/over-half-of-psychology-studies-f...
- https://www.scientificamerican.com/article/psychology-s-cred...
- https://digest.bps.org.uk/2017/05/25/was-the-crisis-in-socia...
I do understand some of that, and probably see more of the psuedo-science application than most: there is a psychological model of occultism folks follow, some of it heavily leaning on Jung's work... who didn't have passable education that we'd like now. And that was pretty common for early psychology: It was more akin to basic philosophy and unbased theories than science.
But I realize that is changing and I realize the good the system really does - my ex was schizo-affective (though he got diagnosed with regular schizophrenia after we broke up). Without the whole system, both the stuff based on shaky psychology and the more pure medical portion with the meds and psychiatrist, he'd have died - no exaggeration.
You don't appear to have presented any evidence or reasons that would make your hostile opinions a useful contribution here.
Methodologies have been devised, reproducible results have actually become an expectation, and psychology has benefited quite a bit from biology, computer science and information theory.