All food is a source of energy, and when eaten, it is broken down in the stomach by acids and enzymes that ultimately begin the process of aerobic cellular respiration, which is essentially the process by which food is converted to energy (or fat). In terms of digestion, there are few roles that desserts play in digestion. One school of thought states that a dessert facilitates digestion by loosening the stomach muscles and pulling water into the stomach to dilute the contents. Sugar also stimulates the vagus nerve which signals the stomach to loosen up.
Then, in Chinese culture, the spleen is considered an organ and is in control of digestion. It is responsible for the processing food from the very beginning, from eating to turning it into energy. The taste related to the spleen is sweet, and so sweets are digested through this particular organ system. Moreover, the functions of the organ can be emotional, physical or symbolic, and in this case, humans have an emotional to sweets because they are often used to self-medicate and we crave them.