Some research suggests that eating foods high in omega-3 fatty acids and vitamin B12 can help to level out mood. Wild salmon, flax seeds, walnuts, cabbage, and brussel sprouts are all good sources of omega-3s, while clams, octopus, liver, crab, and beef are filled with B12. In addition, if possible, avoid caffeine and never skip a meal. This will help you to avoid ups and downs in your energy level that can contribute to mood swings.