To fast (upavasa or anasana) is to go without food for an extended period. Fasting is practised for religious, for health or for medical reasons. It has also sometimes been used for political purposes as Mahatma Gandhi and IRA prisoners did.
Jains practise several types of fasting including what is called Santhana, fasting to death. Muslims are supposed to abstain from all fluids and food between sunrise and sunset during the month of Ramadan. Fasting is frequently mentioned in the Bible (e.g.
Acts 14,23; Luke 2,37; Matthew 6,16; etc.) and Jesus once fasted for 40 days (Matthew 4,2).
Fasting, even extreme fasting, formed a part of the self-mortification (attakilamathāna yoga) practised by ascetics during the Buddha’s time. During the six years the Buddha (or more correctly, the Bodhisattva) was learning from other teachers and experimenting with various ascetic practices he to underwent long fasts.
Some of these as described by him in the Mahasihanāda Sutta included eating only once every seven days, eating only one kola fruit a day (M.I,78). The kola is the fruit of Zizyphus jujube, a small fruit with limited nutritional value.
As a result of these and other fasts the Buddha’s body became extremely emaciated.
‘Because of eating so little my ribs stuck out like the rafters of an old hut, my eyes sunk into their sockets and their gleam looked like the gleam in the on the water in a deep well, my stomach touched my back bone so that when I tried to touch my stomach I got my backbone and when I touched my backbone I got my stomach, all because I ate so little.’ (M.I,80). The famous Fasting Buddha in the Lahore Museum in Pakistan is based on this passage.
Also, during that time they are allowed to take fruit juices and other liquids. Milk is included in the prohibition against food at night but for some unaccountable reason Thai monks ignore the fact that cheese is made out of milk and eat it in the evenings.
Lay people keeping the uposatha will also abstain from food from noon to sunrise the next day. The Buddha’s recommendation to monks and nuns to abstain from food at night seems to have been entirely for reasons of health.
He said, ‘I do not eat in the evening and thus am free from illness and affliction and enjoy health, strength and ease.’ (M.I473). Long fasts such as are recommended by certain ‘health’ practitoners are not good for health and would contravene the Buddha’s concept of talking a middle way (majjhima patipada) and avoiding extremes.