Quick & only slightly pretentious guide to healthy eating based on the simple understanding that every single cell in your body has at some point passed through your mouth. As has all the energy you have.

You would not expect a machine to offer superior performance if it's built from inferior part. You would also not expect great efficiency if it doesn't get great energy.

Same with your body.

This is not to say that you 'are what you eat' - I feel it's more accurate to say 'what you eat is what you're made off'. There are of course other factors contributing to who you are, including your birth-genes, your environment as well as your free will to bend much of the above. :-)

The advice here is not absolute but more like operating principles on making food decisions.