I don't doubt that different body types react differently to food. I don't think, though, that you can ignore the link between poor diet (broadly speaking high in fatty and sugary foods, low in vegetables and fruit), obesity and diseases like Type 2 diabetes in younger people. I agree education certainly has a role to play, which is why schools spend a lot of time on issues related to healthy eating, (though I do wish the DT curriculum had more cooking in it, obviously for boys and girls).
I think one of the main issues in all this though, is the role of the supermarkets and the food "industry" . Did anyone else watch "The Men Who Made Us Fat", on TV recently? The links between the food industry and some politicians were interesting to say the least. The cynical policy of "supersizing", the role of advertising, the suppression of legislation to warn people about the dangers of what they are eating, I found quite shocking.