Fasting in early Buddhism and Theravada
Traditionally, Buddhist monastics follow the prātimokṣa rules outlined in the various Vinayas (texts outlining the monastic discipline) all which specify that one must not eat after the noon meal. Instead, Buddhist texts mention that this is a period which should be used for meditation or sutra chanting. Breaking this rule is considered a pācittika offense which needs to be confessed. This is not considered a kind of fasting, but a simple and moderate way of eating which is said to aid one’s meditation and health. Devout lay persons will also follow this rule during special days of religious observance (uposatha).
In early Buddhism
The Buddha’s Middle Path refers to avoiding extremes of indulgence on the one hand and self-mortification on the other. According to the Early Buddhist Texts, prior to attaining nirvana, Shakyamuni practiced a regime of strict austerity and fasting which was common among the sramana religions of the day (limited to just a few drops of bean soup a day). These austerities with five other ascetics did not lead to spiritual progress but did cause him to become so emaciated that he could barely stand. It was only after he gave up the practice of harsh asceticism, including extreme fasting, and instead focused on the practice of meditation and jhana, that he attained awakening. Because of this experience, the Buddha criticized the fasting practiced by Indian ascetics of his day, such as that practiced by Jains, who believed that fasting burned off bad karma. According to Bhikkhu Analayo:
the Buddha noted that ascetics who underwent periods of fasting, but subsequently resumed eating to regain their strength, were just gathering together again what they had earlier left behind.
Instead, the Buddha focused on practicing mindfulness while eating, a practice he recommended to both monastics and laypersons. According to Analayo, this practice connects the second and third satipatthanas (foundations of mindfulness) , that of mindfulness of hedonic tones (vedana) and mindfulness of the mind (citta) respectively. This allows one to understand how sensual craving arises out of worldly pleasant feelings, and gain insight into the very nature of sensuality (and thus lead to its cessation).
However, the Buddha did end up recommending that monastics not eat anything after noon. This practice could be considered a kind of intermittent fasting, which restricts eating to a specific time period.
One meal a day practice
In Theravada Buddhist monasticism, there are various optional ascetic practices named dhutaṅga (literally “means of shaking off” or “shaking up”, as in to “invigorate”) which are popular with Thai forest monks, several of them have to do with food. One practice is called “one-sessioner’s practice” (ekāsanikanga) which refers to eating only one meal a day.
Another practice consists of only eating food collected on one’s bowl during the daily almsround (piṇḍapāta) where monks go begging for food. If one happens to receive just a little food or not to receive any at all on one particular day, one would have to fast.
Dhutaṅgas are seen as means to deepen one’s spiritual practice, and to develop detachment from material things, including the body.
Fasting in Mahāyāna
In East Asian Mahayana Buddhism, there are different fasting (Chinese: zhai) practices. The most common form refers to a strict form of vegetarianism which also avoids the five pungent foods.
One of the most important forms of fasting historically was the Chinese Buddhist practice termed zhaijie or baguan zhai (eight-fold fast), which became an important practice for serious lay Buddhists during the Han dynasty. During a baguan zhai one was expected to avoid all meat (and fish) and take the eight precepts (and therefore, also includes not eating after noon), and the duration of the fast varied, common forms were a six day fast (liuzhai) and a three day fast (sanzhai). Another form was a long fast (changzhai) which is observed continuously, “in the first half of the first, fifth, and ninth month.” These practices were popular among many Chinese lay Buddhists, including high ranking literati and officials who would gather together to observe fasts. The popularity of the practice may have to do with some Chinese emperors, such as Emperor Ming (465-472) of the Liu Song dynasty, who was a vegetarian and a practitioner of fasting. The eight fold fast was often practiced during certain Buddhist holidays, such as during Vesak.
In the Japanese Buddhist sects of Tendai and Shingon, the practice of total fasting (danjiki) for a length of time (such as a week) is included in the qualifications of becoming an ajari (acarya, a master teacher). The Tendai school’s grueling practice of kaihōgyō ends with nine day period of fasting.
Fasting is also practiced in Korean Seon Buddhism, as a supplement to meditation and as part of a training called geumchok. The East Asian Buddhist practice of self mummification (sokushim-butsu) also includes intense fasting.
In Tibetan Buddhism
The Vajrayana practice of nyungne is based on the outer tantra practice of Chenrezig and traced back to an Afghani Buddhist nun named Gelongma Palmo. It is said that Chenrezig appeared to an Indian nun who had contracted leprosy and was on the verge of death. Chenrezig taught her the method of nyungne in which one keeps the eight precepts on the first day (as well as eats purely vegetarian), then refrains from both food and water on the second.