The spell damage stat is not increased - the tooltip damage of abilities is. Think of "spell damage" in your character screen as "spell power", and the damage dealt is then calculated from "spell power", maximum magicka and a bunch of strange coefficients.
So, food does affect your damage, in that the maximum magicka number goes into the calculation of each and every magicka consuming ability.
Septimus_Magna wrote: »Next time also check the tooltip dmg from an ability