Complex carbohydrates, such as sweet potatoes, are packed full of energy and mood-boosting vitamins and minerals. Like many other mood-influencing foods, sweet potatoes boost serotonin production. Sweet potatoes act as a referee of sorts because they contain carotenoids, which are responsible for insulin regulation. Correctly managing insulin helps us avoid sugar crashes that cause irritability. The miracle food also contains potassium, which has been shown to reduce mood swings, increase energy levels and lessen tension [source: Melone]. Although many dieters malign carbs of all shapes and sizes, low-carbohydrate diets have been linked with a reduced desire to exercise and increased fatigue in overweight adults [source: Magee]. The health quotient for this popular holiday dish can be amped up by cutting back the amount of butter used in preparation and by including walnuts, which are an excellent source of tryptophan.