i like to use the 'adam and eve' method, which is, if it didnt exist in bible times, i try not to eat it. this means vegetables, fruits, certain breads, milk (a la WHOLE) and dairy, fish, grain-fed animals, etc. are okay. basically, as little processed food as possible- no canned veggies/fruits, majority of snack foods, blah blah blah.
two things to note:
1) i enjoy processed foods as well, im not as i strict as that came across. i love ice cream (marry me!) and popcorn and sour patch kids, i merely remember to eat them rarely and in moderation.
2) take the terms in this post lightly, with a grain of salt. i dont want to turn the fitness thread into a "what people really ate in the bible" discussion when all im really trying to say is, "keep it natural".