An interesting book was this geneticist's book 'The Diet Myth' http://www.tim-spector.co.uk/ which is a critical look at nutrition myths such as fish oil supplements though it has low signal to noise ratio, way too many personal stories.

Maybe look at university department pages to see what kind of research they're publishing, or look at at their course offering to read the same material such as: https://online.usc.edu/programs/master-of-science-in-nutriti... they're using the book 'Gropper. Advanced Nutrition & Human Metabolism 7th ed' in some of the courses.

For cheap food I buy shares in a community supported agriculture (CSA) program that delivers food weekly through the season.