This is an interesting study from Japan claiming that a breakfast of rice (as compared to bread), in children, not only leads to higher overall grey matter amonunts and specific regional changes in both grey and white matter, but also higher IQ.
As a caveat, gross morphological changes in grey/white matter are not a good measure of intelligence, and even IQ must be interpreted with great caution.
And the reason why? The researchers hypthesise that it is because rice has a lower glycemic index than bread.
Food for thought.