The earliest instances of fasting dates back to ancient times, when people fasted under the belief that it cleansed their spirits. Since then, religion, spirituality, weight loss, detoxification, medical testing, and surgery have all become reasons that people fast. In some religions and spiritualities, fasting is still a way to cleanse and purify the body and soul, and is considered a sacrifice. Fasting can also be used to lose weight in cases of morbid obesity. Some individuals use fasting as a means to detoxify their body. Other times, medical testing or surgery may be cause for fasting.