Although hormone imbalance is the root cause of PMS, a number of other factors can fuel the fire. Too much sugar can lead to a loss of magnesium, which in turn makes bloating worse. (So much for that bad-mood-soothing brownie.) Caffeine, low calcium and stress can also ramp up PMS. Cutting down on coffee for that week, snacking on low-fat string cheese and hitting up a yoga class might help mitigate menstrual misery.