Catholicism teaches that gluttony is a sin when excessive eating or drinking impairs one's health or mental capacities. In most cases, gluttony is considered a pardonable sin, but there are people for whom, as St. Paul wrote, their "god is in their belly" (Phil. 3;19), and this constant overindulgence, and especially impairment because of it, would be a mortal sin. In Summa Theologica, St. Thomas Aquinas wrote that gluttony is indeed a sin, but it is not the greatest of sins.
Orthodox Christianity emphasizes self-control in humans, and restraint in eating is seen as one of the foremost indications of self-control. Gluttony is considered a capital, or mortal, sin. The consensus of the early church is "stop eating while you are still hungry and don't allow your stomach to be filled to satisfaction," according to the 4th-century saint John Cassian. Overeating is associated with the dulling of intelligence and a decreased ability to guard against temptations. Orthodox Christians believe that, as humans fell initially through eating (when Adam and Eve took the apple in the Garden of Eden), people must have a proper relationship with food to restore themselves to union with God. Orthodox Christians also abstain from certain foods during fast periods to gain strength in self-control.
Mormons are often thought of as the poster-children of self-control, with many dietary and other restrictions, including no tobacco, alcohol, tea, coffee, or other caffeinated foods. Brigham Young reportedly said, "The greatest curse of the latter days will be gluttony." Mormons fast on the first Sunday of every month, in hopes that it will bring them closeness to God. A strict health code, called the Lord's Law of Health, emphasizes taking good care of one's body and avoiding excess eating. It states, "Because our bodies are important, our Father in Heaven wants us to take good care of them. He knows that we can be happier, better people if we are healthy."
Hinduism teaches the importance of avoiding excess in several areas of life, including food consumption. The Hindu text the Tirukkural warns against overeating: "The thoughtless glutton who gorges himself beyond his digestive fire's limits will be consumed by limitless ills (95:947)."
The Hindu health system of ayurveda teaches that certain foods have spiritual elements. Proper intake of these foods keep the psyche and intellect in balance.
Contrary to a common perception, Hindus are not required to follow a vegetarian diet. Many Hindus do observe religious dietary restrictions by practicing vegetarianism. However Hindus are often vegetarians because they adhere to the principle of ahisma, or non-injury, rather than due to practicing self-restraint.
While members of other religions often fast for a day at a time to strengthen their resistance to gluttony, Muslims fast for an entire month. The fast--no eating or drinking--during the holy month of Ramadan lasts from sunrise to sunset. Other prohibitions during the month include smoking and sex. The fast and other laws in Islam help Muslims eschew gluttony. As the Qu'ran says, "O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may learn self-restraint (Al-Baqara, Surah 2:183)." Muslims are also discouraged from being too gluttonous when breaking the fast with the iftar meal., which is eaten immediately after sunset.