Fasting has spiritual, societal and health benefits. The spiritual benefits include the practicing and strengthening of one's patience, knowing how to control oneself and help oneself in that realm. The soul finds within itself the ability to have taqwa (fear of Allah) and to improve upon it.
Societal benefits include the fact that it adds a certain system and unity to the society, engenders love for justice and equity, brings about mercy and compassion among the believers as well as good behavior. Furthermore, it keeps the society from evil and wickedness.
Health benefits include the purifying of the intestine, improving the health of the stomach, cleansing the body of impurities, decreasing the level of fat in the body and decreasing the heaviness of the stomach due to fat.
Information from
Fiqh Made Easy - A Basic Textbook of Fiqh
by Dr. Saalih ibn Ghaanim al-Sadlaan