Fact is there is just not much science on "diet". There is enough however that your ethnic background can have a large effect on exactly a healthy diet is. About all we can really say is that too much of anything is bad, to little of somethings is bad. Get some exercise, even if it is just 10mins walking a day, we know that makes a difference.
However we have some really interesting results recently (I go to these sorts of conferences). If you are starved in your younger years, like before 10, or your mother was starved during pregnancy, this has a fairly irreversible (we think) effect on your metabolism that makes your body hoard all it possibly can.