Proof that a healthy diet pays off?

According to a study just published by the Institute of Social and Economic Research it looks like the fantastic work Jamie Oliver did improving the food in Greenwich has led to a fall in the abscence rate of 15% and an increase in SAT scores.

I completely agree that as the School Food Trust say so succintly "eat well - do well". Children are bound to do better if their diet dramatically improves. But there is a part of me that is really nervous about tying the need for good food for school children to exam scores.

Firstly, I have no confidence in SAT's as an indicator of anything other than a schools ability to teach children to score highly on SAT's. Secondly, even if an improved diet did not lead to improved exam scores I would still be leaping up and down demanding children get decent food.

It's a strange old world we live in when we have to "prove" that there is a clear correlation between achievement and diet when the medical profession has long since established that a healthy diet containing fuit and veg is the best way to improve health chances.