Some foods help us to be more cheerful. For instance, foods that elevate serotonin level, like carbohydrates, or sugars that comfort us when we are stressed out. The trick is to eat healthy to be happy. So when we crave carbs, whole grains should be chosen over refined products.
As for sugar, a little bit goes a long way. Too much of sugary desserts boost the level of sugar in the blood which can create problems.
So a small amount of sweets, only a few bites should be aimed for. Often fruit will satisfy the need for sweets, and ultimately make us feel better, over the sugar loaded snacks or desserts.