[dejb]

> Eat a bowl of cereal in the morning (and I mean something like oatmeal or raisin bran rather than some sugary crap) and it barely matters what else you eat (other than calorific content)

I think you are seriously overestimating the nutritional value of a bowl of cereal, even a relatively healthful one. You may not see the worst of the consequences until you reach your 30s but they will still be accumulating.