Back-to-school season seems as good a time as any to think about boosting your kids’ brain power, not to mention your own. But this year, instead of flashcards and multiplication drills, you might want to focus on the family diet. “Food can affect the brain in minutes,” says neurologist Majid Fotuhi, chairman of the Neurology Institute for Brain Health and Fitness in Baltimore. “You don’t need scientific evidence to know that if you have a doughnut, after a while — it could be minutes or an hour — you feel tired and drained because of the spike in blood sugar, …