Via negativa: Avoid what is most likely bad (food processed by industry, sodas, excess sugar, excess salt, trans fat and food blogs). Beyond that there isn't too much you can do.
If one wants to embark on a moral argument present in the theory of evolution, where no organism is more special than the other, then you'd probably avoid consumption of food coming from animals, or you'd be setting yourself up to some contradiction in the brain. :D Or, if one wants to embark on a moral argument that humans are special and that life is worth conserving. Then, you'd probably also want to not include a…
For example, ants keep aphids for honeydew just as humans keep animals for dairy products.