1) This maxim from Michael Pollan: "Eat food [1]. Mostly plants. Not too much." (I personally follow an adjusted version of this: "Eat food. Only plants. Not too much.")
2) Review daily nutrient requirements to ensure your diet is providing you with adequate macro (protein, carbs, fat) and micronutrients (vitamins, minerals).
3) A few months after adopting your new diet, get a high quality blood test that covers markers like iron, B12, etc., and make any required adjustments to what you're eating.
1: "Real food doesn’t have a long ingredient list, isn’t advertised on TV, and it doesn’t contain stuff like maltodextrin or sodium tripolyphosphate. Real food is things that your great-grandmother (or someone’s great-grandmother) would recognize." https://michaelpollan.com/reviews/how-to-eat/
It's almost like a second job to keep up with what you _should_ do. Reviewing daily nutrients is way too much effort for most folks.
It isn't so much managing daily nutrients but ensuring there is a decent variety of nutrients available at home. There is a lot of trial and error but long term it works out well. And like you said, variety is key!
Once you grok some trivially simple stuff (macro and micronutrients), few extremely trivial requirements (enough good sleep, stay away from sweet stuff in principle which may be hard in beginning but gets much easier over time, eat to stave off hunger and not to feel full, eat less in the evening), you are at least 90% there which is already enough. You really don't need to study constantly labels, you already know whats good and bad and its an effortless background process in the back of the mind.
It really is trivial and very quick to grok. The hard part for many is discipline, thats a mind game everybody has to fight with themselves and find ways how to manage it without frustrating oneself constantly, and thus give up eventually on whole effort.
People often compensate some deep mental issues, ie anxiety with overeating or eating junk food. Obviously this needs to be tackled first if any long term success can be claimed.
Also, for parents, please don't condition your kids on sweet stuff as some sort of reward. If you have to, use some great fruits like forest fruits and not cakes, ice cream etc. You are not being a good parent at all by doing this, just conditioning them mentally that sweet junk is something special, a prize deserved, which creates pretty bad mental patterns for rest of our lives.
I don't disagree with your assertion on steps, to be clear, just that you aren't answering the actual question. How can you trust Pollan (I'm not saying you can't, just...that's the core question the OP was asking).
While I agree with the spirit of this, I'll point out that tobacco was brought to Europe over 500 years ago, and only recently discovered to be one of the most unhealthy products available. Not to mention that it was widely used in the Americas for long before that.
In fact, 450 years after Columbian contact, the medical consensus was that tobacco was good for health.
Ugh, if we hadn't banned them from advertising they would absolutely be using this angle and it would absolutely be working.
Why not just look at the balance of evidence for various dietary patterns today?
https://www.redpenreviews.org/reviews/eat-drink-and-be-healt...
Here's a two hour interview with the author if you prefer the format: https://www.youtube.com/watch?v=Dx2JUtngxkw
Identify people you trust on a subject, filter their claims through your own ideas about what is reasonable, and hope for the best.
You might still get it wrong. Such is life.
There is of course a lot of kooky beliefs out there about food. But it seems like there is a very intentional social media campaign to associate ANY claim that the stuff in our food is not in our best interest with the kooks that believe the only safe thing to eat is raw goat balls or whatever.
For books anyway, I found The Hundred-Year Lie to be incredibly in depth, but there's a lot of chemistry so it's verrry dense.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8227014/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9776645/
Remember, the test of a true intellectual is that they can convincingly defend a position they find abhorrent.
― John Stuart Mill, On Liberty