It’s not that hard, eat what your grandparents did.
Most of the dietary problems came from junk science in the 1960s and ‘70s, like “salt is bad”, “Soy is a wonderfood with no ill effects!”
Everything else is marketing, more junk science, and snobs looking for something to brag about. There’s no need to avoid gluten if you don’t have Celiac disease.
Also the fat free nonsense. Brains love fat. I researched this because my son’s pediatrician wanted to put him on a low fat diet when he was an infant. After reading about the brain being the fastest growing organ for an infant and that brains love fat, I did not change his diet. He was heavy but all that weight fell off once he started walking.
Depending on what your grandparents ate, that could be dangerous too! In the old days, many people ate lots of lard and butter. I'm talking about them giving big sticks of butter to their kids to gnaw on like it was a corn cob. I've seen fat people doing this in Kansas to this day. Also lard was eaten, without being used for cooking first. And used lard was poured in a coffee can after frying, and reused again and again. A lot of people in older generations had bad teeth (or no teeth at all) because of the crap they ate.
Just eat sensible. This organic thing is a fad.