Eat only whole foods. Buy no grain that is less than 10% fiber (I personally make an exception for short grain brown rice, which is about 9% fiber). Buy nothing that comes in a container unless it has 3 or fewer ingredients, all of which you can name. Eat lots of whole grains and vegetables, a little fruit, and a little meat/dairy. Enjoy extra virgin olive oil and vinegars for flavor.
Heavily limit sugar, regardless of where it comes from (this means fruit, too!).
This is also a cheap and planet-friendly way to eat. Almost like it's meant to be.
That's my thing, anyway.