Eat them: These cousins of the standard English walnuts you’re accustomed to eating may keep you happy as long summer days wane. They contain some of the highest levels of serotonin, a neurotransmitter that keeps your mood and stress levels in check, of any food.
Find them: Black walnuts can be found in the nut aisles of most gourmet grocery stores, but why pay the high price of $12 to $13 per pound? This time of year, black walnuts are practically raining off walnut trees, which grow across the U.S. Look for trees that bear green, baseball-sized fruits and pick up any that have fallen on the ground. Crack open the green exterior (but wear gloves, because the brown flesh on the inside will stain your fingers), and you’ll see the black walnut hiding inside.