Synthetic chemicals in food system creating health burden of $2.2tn a year, report finds
(www.theguardian.com)
Don't worry about the details, whole foods are the best foods. That is where you buy whole ingredients as they come directly from the farm (or as close as you can get). Shop the outside edge of your grocery store. Don't buy anything from a box, or wrapped in plastic, or from a petrochemical plant (including oil). Look at the ingredients for everything you buy, and if it's complex or you can't pronounce it, don't buy it.
Bonus points for organic and avoiding pesticides
This is probably overkill, but it avoids lots of the new advances in food and processing in the last 100 years which coincides with the rise of modern non communicable diseases.