Orthodox Christian Fasting
Lenten & Liturgical Fasting
Evidence grade 2 of 5, Thin. Read how the Atlas grades evidence.
0 human trials, about 17 studies, Millions (lifetime). The written rationale for this grade is still being prepared.
- FDA
- Religious practice
- WADA
- Not prohibited
Reference only. Not medical advice.
What can go wrong
Over long fasting periods, poorly planned menus are associated with low vitamin D, vitamin B12, and calcium intake; a Mount Athos monk study observed profound vitamin D deficiency. Lipid and weight changes seen during a single fast may not persist once normal eating resumes. Fasting is an eating-behavior practice with real exemptions within the tradition itself, and the Orthodox Church teaches it should never be done to the detriment of health. Anyone who is pregnant or nursing, who is managing a medical condition such as diabetes, who is caring for a child, or who has any history of disordered eating should consult a qualified clinician and, within the tradition, a priest or spiritual father before undertaking extended fasting. This entry is informational and is not dietary, medical, or pastoral advice.
Orthodox Christian fasting is a periodic, largely plant-based abstinence woven through the Eastern Orthodox liturgical calendar, covering roughly 180 to 200 days a year across four multi-week fasts and weekly Wednesday and Friday observance. On strict days adherents abstain from meat, fish, eggs, dairy, and often olive oil and wine, shifting toward legumes, vegetables, grains, fruit, and shellfish. Observational studies of practitioners, from Cretan laypeople to Mount Athos monks, are associated with lower total and LDL cholesterol and lower BMI. No randomized trial exists, so the evidence is preliminary and observational rather than experimental. The tradition carries built-in exemptions for the sick, pregnant and nursing women, children, and the elderly through the pastoral principle of oikonomia.
A periodic plant-based fast practiced for centuries, with quietly strong cardiometabolic data.
What people take it for
These are the reasons people give for taking it. They are not effects it has been shown to have.
What people get wrong
Often saidReligious fasting is too irregular to study
ActuallyOrthodox fasting follows a fixed liturgical calendar of roughly 180 to 200 defined days a year, which is why researchers from Sarri et al. (2003) to Karras et al. (2017) could measure practitioners across known fasting and non-fasting periods.
Often saidThe science behind Orthodox fasting is RCT-grade
ActuallyIt is not. Per Koufakis et al. (2017) and the 2023 Nutrients clinical-evidence review of 17 studies, no randomized controlled trial exists; the data are observational, so findings are associations, not demonstrated cause.
Often saidOrthodox fasting is nutritionally complete by default
ActuallyCross-sectional data from Mount Athos monks (Karras et al. 2017) show profound vitamin D deficiency and elevated parathyroid hormone, and reviews flag reduced B12 and calcium intake, signals that planning matters over long fasting stretches.
Often saidOrthodox fasting is the same as veganism
ActuallyOn strict days it excludes animal products, but the calendar permits fish, oil, and wine on many days and always allows shellfish, making it a periodic, partial plant-based pattern rather than continuous veganism.
Who profits, and who pushes back
Theodoros Koufakis and colleagues
Koufakis et al. conclude that, given limited and sometimes conflicting data, more studies are required before reaching definite conclusions about the effects of Orthodox fasting on human health, with the impact on body weight and glucose homeostasis unclear.
Spyridon Karras and the Mount Athos study team
The Karras et al. team report profound hypovitaminosis D (about 8.8 ng/mL) with elevated parathyroid hormone in strictly fasting monks, identifying reduced vitamin D, B12, and calcium intake as the practice's main nutritional downside.
Nasrin Gholampoor, Duane Mellor and colleagues
Gholampoor et al. pooled observational studies rather than trials, finding an association with lower total cholesterol while noting the evidence base lacks the randomized designs needed to confirm a causal cardiovascular benefit.
Eastern Orthodox tradition
A centuries-old liturgical practice with structured fasting periods and built-in exemptions.
Greek nutrition researchers
Have documented favorable lipid and BMI patterns in observant Orthodox Christians.
Where the research comes from
| Place | Share of published research |
|---|---|
| Eastern Europe | 40% |
| Greece | 34% |
| Other | 26% |
Research published from: Greece, Eastern Europe, Global.
How we got here
Orthodox fasting grew from the earliest Christian communities of the eastern Mediterranean and Near East, not from later Western Europe. The Didache, a Greek text of the first or early second century, already directs believers to fast on Wednesdays and Fridays, distinguishing them from contemporary Jewish practice. Through late antiquity the discipline expanded across Byzantine, Greek, Slavic, Coptic-adjacent, Levantine, and Caucasian Christian lands into a detailed calendar: Great Lent before Pascha, the Apostles' Fast, the Dormition Fast in August, and the Nativity Fast, plus weekly fasts, totaling nearly half the year. Monastic communities, above all the monasteries of Mount Athos, preserved the strictest form. The pattern has been practiced continuously for more than a millennium across the Orthodox world. Only in the 2000s did Greek nutrition researchers begin documenting it as a real-world model of periodic plant-based eating, decades after the tradition itself.
- c. 50-110 CEThe Didache directs Christians to fast on Wednesdays and Fridays, the earliest written witness to the weekly pattern
- 300s-600s CEGreat Lent and the seasonal fasts take shape across the Eastern Church; the six-week-plus-Holy-Week structure is fixed by the sixth century
- c. 900s onwardAthonite and Slavic monastic typika codify the strict fasting calendar that persists today
- 2003Sarri et al. publish a one-year cohort in BMC Public Health: fasters show lower end-period total cholesterol, LDL, and BMI than non-fasters
- 2017Koufakis et al. systematic review (Eur J Nutr) and Karras et al. Mount Athos cross-sectional study (Eur J Clin Nutr) document favorable lipids alongside vitamin D deficiency
- 2022Georgakouli et al. Holy Week before-after study (Diseases) finds favorable shifts that revert within one week of resuming a normal diet
- 2024Gholampoor, Sharif and Mellor meta-analysis (Nutr Metab Cardiovasc Dis) pools observational data: total cholesterol -0.52 mmol/L
At a glance
- Pattern
- ~180-200 fasting days/year
- Form
- Plant-based, no animal products
- Tradition
- Eastern Orthodox
- Evidence
- Favorable lipid data
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Orthodox Christian Fasting. A short entry is not a safe entry.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
Sources
One-year cohort of 60 fasters vs 60 controls shows lower end-period total cholesterol, LDL, and BMI in fasters
Systematic review of 10 studies; consistent total cholesterol and LDL reductions, HDL unclear, weight and glucose inconclusive, reduced vitamin D/B12/calcium intake, no RCTs
Review of 17 clinical studies states all were observational with no randomized controlled trials; notes B12, calcium, and vitamin D concerns
2024 meta-analysis of 14 studies (10 pooled, 755 fasting/661 control); Orthodox fasting associated with total cholesterol -0.52 mmol/L (95% CI -0.64, -0.39)
Cross-sectional study of Mount Athos monks: favorable lipids and glucose but profound vitamin D deficiency (8.8 ng/mL) with elevated PTH; confirms 180-200 fasting days/year
Holy Week before-after study (n=23): favorable body composition and cholesterol shifts during fasting that revert within one week of resuming normal eating
First or early second century Christian text directs fasting on Wednesdays and Fridays, earliest witness to the weekly Orthodox fasting rhythm
OrthodoxWiki, Fasting (citing the Didache and patristic sources)
The four seasonal fasts, weekly Wednesday/Friday fasts, and abstained foods (meat, fish, eggs, dairy, oil, wine; shellfish permitted)
Tradition exempts the sick, pregnant and nursing mothers, young children, and the elderly via the pastoral principle of oikonomia; fasting should not harm health
St. Michael Antiochian Orthodox Christian Church, What if I have health issues and can't fast?