+1 If you eat what you need when you're hungry, and stop short of overeating, all should be well. Those paradigms change if the body doesn't function quite right (diabetes, eating disorders, etc) but overall nothing's changed in 1000s of years. If you stick to real food (made from scratch) where possible and avoid processed food as much as possible, there shouldn't be a lot of guess work in ones diet. Hard part is finding those whole foods and un-altered starting products to work with.