The author Michael Pollan summed it up fairly well with "Eat food, not too much, mostly plants."

When in doubt, try to think what humans evolved to do and to process, and try to mimic that.

For nutrition, did we evolve with enormous servings of fast food, donuts, and spend millions of years eating highly refined highly concentrated packaged garbage packed full of preservatives, chemicals, and mystery substances, all consumed in absurd quantities? Or did we evolve to eat a diverse range of plants with occasional proteins and meats?

For health and exercise, did we spend millions of years sitting around watching TV and being screen sloths? Or did we spend millions of years walking dozens of miles every day, with near constant physical activity in some form or another?

As for studies and raw data, NIH pubmed https://www.ncbi.nlm.nih.gov/pmc/, NHS, EU, all have interesting raw largely non-opinionated information to scan through.