@bythewell - It's not just the health concerns that should influence your buying habits.
Export certificates of origin can also show you if food has been shipped from a long distance, using up fossil fuels, which contribute to global warming.
You might also want to avoid buying things that you know have been grown in bad circumstances like palm oil from Indonesia. They are cutting down rain forest in order to grow it, so boycotting the product might help to stop that.
Often the origin of some of the products is obscured though, because current certification processes only require one country to be named, and lots of products are made up of things from several countries.