Why humans have practised fasting for centuries

Three threads of human fasting history

Fasting recurs across human cultures and centuries for three main reasons.

1. Religious and spiritual traditions

Every major world religion incorporates fasting in some form. Islam: Ramadan (the lunar month of dawn-to-sunset fasting), plus voluntary fasts on Mondays, Thursdays and white days. Christianity: Lent (40 days of various restriction in Catholic, Orthodox and some Protestant traditions), Friday abstinence historically, Orthodox Wednesday and Friday fasts. Judaism: Yom Kippur (25 hour fast) plus Tisha B'Av and several other fast days. Buddhism: many traditions involve afternoon and evening fasting, with strict monastic traditions practising more extensive fasts. Hinduism: numerous fasting practices on specific lunar days or for specific deities. Bahá'í: a 19 day sunrise-to-sunset fast. The recurring theme is using fasting for spiritual focus, self-discipline and reflection.

2. Medical and therapeutic tradition

Hippocrates (around 460 to 370 BCE) and Galen (around 129 to 216 CE) advocated therapeutic fasting in various conditions. The commonly cited Hippocratic principle that food during illness can feed the illness reflects an ancient medical tradition of using fasting for recovery. Medieval and Renaissance European medicine continued therapeutic fasting practices. Traditional Chinese medicine, Ayurvedic medicine, traditional Persian medicine and other systems all include therapeutic fasting protocols. Modern medical fasting emerged in the early 20th century with Otto Buchinger establishing his fasting clinic in 1920. The Buchinger Wilhelmi clinics continue today with over a century of clinical experience.

3. Cultural and survival contexts

Pre-industrial human societies experienced involuntary fasting routinely. Hunter-gatherer societies experienced periods between successful hunts or foraging. Agricultural societies faced seasonal scarcity between harvests, lean winter months and crop failures. Famines have occurred in recorded history with regularity. Bodies unable to function during food-scarce periods would not have survived. The metabolic capacity to fast is an evolved adaptation to involuntary fasting that was a regular feature of human life. Modern abundance of food represents a recent historical anomaly not the norm.

4. The unifying observation

Across these three threads one observation stands out: humans tolerate fasting well. The body is designed to handle alternating fed and fasted states. The practices range from millennial religious observances continuing today to documented therapeutic practice for over a century. This convergence does not prove specific health benefits of modern intermittent fasting protocols but it establishes that fasting is normal human physiology rather than novel exotic biology.

Five enduring fasting traditions in detail

Each major fasting tradition has distinctive features worth understanding.

Ramadan (Islam)

Around 1.8 billion Muslims worldwide observe Ramadan annually. Fasting from dawn (Suhoor) to sunset (Iftar) for the lunar month. No food or drink including water during daylight. Duration varies by latitude and season from around 11 to 20 hours. Eating happens at Iftar (the breaking of the fast at sunset) and Suhoor (the pre-dawn meal). Exemptions for pregnancy, breastfeeding, illness, travel, children, elderly and those with significant medical conditions. Ramadan is the most extensively studied natural intermittent fasting model in modern research.

Lent (Christianity)

40 days from Ash Wednesday to Easter in Western Christian traditions. The exact practice varies: historical Catholic Lent involved one main meal per day with no meat. Modern Catholic practice typically involves abstinence from meat on Fridays and personal commitments to give something up. Orthodox Christian Lent (Great Lent) is more rigorous involving abstention from meat, dairy, fish, wine and oil at varying degrees. Protestant traditions vary widely from minimal observance to detailed practices.

Yom Kippur (Judaism)

The Day of Atonement: 25 hour fast from sundown to sundown the following day. No food, no water. Most rigorous and widely observed Jewish fast. Other Jewish fast days include Tisha B'Av (mourning the destruction of the Temple, 25 hours), Fast of Esther, Fast of Gedaliah and others. Exemptions for illness, pregnancy and similar circumstances. Yom Kippur fasting has been studied for various health markers.

Buddhist and monastic fasting

Many Buddhist traditions involve eating only before noon with no food after midday. Theravada monks traditionally eat one or two meals before noon and nothing after. Mahayana traditions vary. Some Buddhist traditions involve longer episodic fasts. The practice supports meditation and contemplative life. Catholic monastic orders similarly include various fasting practices.

Modern medical fasting (Buchinger Wilhelmi tradition)

Established 1920 by Otto Buchinger in Germany. Clinic-based therapeutic fasting programmes typically 7 to 21 days under medical supervision. Combine water fasting with small amounts of broth, juice or honey water (around 250 to 500 kcal per day). Continuing operation today with over 100 years of clinical experience documenting therapeutic fasting in chronic disease contexts. The modern intermittent fasting research builds on this tradition but the protocols are different (much shorter, no medical supervision needed for short fasts).

Lessons from historical practice

Historical fasting traditions illustrate several enduring lessons.

• Exemptions matter. Every religious tradition explicitly exempts pregnant women, the sick, children and the elderly. The same contraindications apply to modern fasting.
• Supervision matters for extended fasting. Modern medical fasting (Buchinger Wilhelmi) explicitly developed within clinical supervision frameworks.
• Community matters. Ramadan, Lent, Yom Kippur are practised within communities not in isolation. Modern fasting can be lonely without similar support structures.
• The combination with other practices matters. Religious fasting traditionally combines with prayer, reflection, charity. The full practice differs from extracted dietary protocol.
• Historical practice does not prove modern health claims. The fact that humans have fasted for centuries does not validate specific modern claims about cellular autophagy, longevity, etc. Those claims need modern evidence.

Standard fasting contraindications apply: eating disorder history, pregnancy or breastfeeding, type 1 diabetes or insulin dependent type 2 diabetes, BMI under 18.5, children, adolescents and adults under 18. Anyone on medications or with significant medical conditions should discuss with their GP first.

More on fasting fundamentals

Several pages cover related fundamental topics. Our piece on what fasting is from a physiological perspective covers the underlying biology. Fasting myths and misconceptions covers what modern claims do and do not stand up. And intermittent fasting explained covers the modern protocols.