Another point that doesn't get a lot of press is variability of digestive efficiency. Just because you eat it doesn't guarantee it gets into your bloodstream. This can be your personal GI workings and/or the form the food is in. A good example is peanuts. You will get a lot more calories out of peanut butter than whole peanuts, just because the whole ones don't break down very well especially if you don' chew them up well. I think personal experience is the only thing that will really tell you what and how much you need to eat.