Ramadan Fasting
Dawn-to-Sunset Daily Fast
Evidence grade 3 of 5, Mixed. Read how the Atlas grades evidence.
0 human trials, about 200 studies, >2 participants billion practitioners (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
Ramadan is first a religious obligation, and the tradition itself exempts those for whom fasting would cause harm, including the ill, the traveler, the pregnant and breastfeeding, the menstruating, and the frail elderly. The main documented clinical risk is hypoglycemia in people with diabetes, especially those on insulin or sulfonylureas; international diabetes bodies advise a pre-Ramadan medical assessment and risk stratification before deciding to fast, and observational data show many people fast against medical advice. Daytime dehydration, sleep loss, and circadian disruption from late-night eating are also documented. Anyone who is pregnant or breastfeeding, has diabetes or another chronic condition, takes regular medication, or has a history of disordered eating should consult a qualified medical or religious authority before fasting rather than relying on general information.
Ramadan fasting is the Islamic obligation to abstain from food and drink from dawn to sunset for the lunar month of Ramadan, one of the five pillars of Islam, observed by a large majority of roughly two billion Muslims. Because it recurs every year at population scale, it is often described as the world's largest natural experiment in dry-daytime intermittent fasting, and a deep observational literature documents associated changes in weight, lipids, and glucose. That literature is dominated by before-and-after cohort studies rather than randomized trials, is highly heterogeneous, and finds that most measured changes are transient and largely regained within weeks. The outcome is associated far more with what and when people eat after sunset than with the daytime fast itself. For people with diabetes the practice carries documented hypoglycemia risk, and clinical bodies advise a pre-Ramadan medical assessment before fasting.
The world's largest annual fasting experiment. Dawn-to-sunset, food and water, for a lunar month.
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 saidRamadan reliably causes lasting weight loss
ActuallyMeta-analyses of before-and-after cohorts find modest weight loss during Ramadan (about 1.2 to 1.3 kg) that is mostly regained within 2 to 5 weeks; Fernando 2019 reported body-composition measures returning to baseline after Ramadan, and Sadeghirad 2014 concluded changes are 'mostly reversed.' The fast is associated with a temporary dip, not durable loss.
Often saidThe metabolic benefits are proven by strong trials
ActuallyThere is no randomized controlled trial of Ramadan fasting itself; Sadeghirad's meta-analysis states this directly, citing the religious nature of the practice. The metabolic literature is observational and highly heterogeneous (lipid meta-analysis I-squared 82 to 93 percent), so findings are best read as associations, not proof.
Often saidSkipping water all day is dangerous for everyone
ActuallyFor most healthy adults the daytime restriction is tolerated, which is part of why the tradition itself grants exemptions; risk concentrates in specific groups, notably people with diabetes on insulin or sulfonylureas, where documented hypoglycemia risk warrants medical planning.
Often saidThe fast itself drives the result
ActuallyReviews of meal timing find the result tracks the post-sunset eating window: BaHammam and Almeneessier note that when meals stay in early-evening and predawn periods with adequate sleep the circadian rhythm is not disrupted, while large late-night eating is associated with worse markers.
Who profits, and who pushes back
Ahmed S. BaHammam
BaHammam and Almeneessier report that 'eating during the wrong time of the day results in a misalignment between the peripheral circadian clocks and the central biologic clock,' and that the circadian rhythm is not disrupted only when Ramadan meals stay in the early-evening and predawn periods with adequate sleep; large late eating is the risk.
Behnam Sadeghirad and colleagues
The authors state that no randomized controlled trial of Ramadan fasting has been done because of its religious nature and conclude that 'body weight variations during Ramadan fasting are mostly reversed after Ramadan,' so structured lifestyle change, not the fast alone, is what produces lasting results.
IDF-DAR Diabetes and Ramadan Alliance
The alliance advises that every patient with diabetes who intends to fast be screened with a pre-Ramadan risk calculator, with moderate-to-high-risk patients advised against fasting, reflecting documented hypoglycemia risk on insulin and sulfonylureas.
Islamic tradition
A religious obligation practiced for fourteen centuries, with built-in exemptions for the ill, pregnant, traveling, and others.
Ramadan-health researchers
A large body of observational research, much from Middle Eastern and South Asian institutions, characterizes its metabolic effects.
Where the research comes from
| Place | Share of published research |
|---|---|
| Middle East | 38% |
| South Asia | 26% |
| Africa | 18% |
| Other | 18% |
Research published from: Global (Muslim world).
How we got here
Ramadan fasting was prescribed for Muslims in the second year after the Hijra, around 624 CE in Medina, on the Arabian Peninsula, and it sits among the five pillars of Islam as one of the most widely observed. Its scriptural basis is Surah Al-Baqarah, where fasting is described as decreed 'as it was decreed upon those before you,' situating it within an older Near Eastern and Abrahamic fasting lineage rather than presenting it as new. The same verses name the month of Ramadan as when the Quran was revealed and grant concessions: the ill and the traveler may make up an equal number of days later. For fourteen centuries the practice has been sustained across the Arab world, Persia, South and Southeast Asia, sub-Saharan and North Africa, the Turkic world, and a global diaspora, with Pew surveys finding a median of 93 percent of Muslims across 39 countries reporting that they fast. Modern metabolic interest is recent and secondary to the religious meaning.
- c. 624 CEFasting in Ramadan prescribed in the second year after the Hijra (Surah Al-Baqarah 2:183-185), establishing it as a pillar of Islam
- 7th century onwardPractice spreads with Islam across Arabia, Persia, North and sub-Saharan Africa, South and Southeast Asia, and the Turkic world
- 1990s-2000sEPIDIAR (2001, 12,243 patients, 13 countries) quantifies how many people with diabetes fast, opening clinical study of Ramadan risk
- 2010CREED multi-country observational study documents type 2 diabetes management and outcomes during Ramadan
- 2012-2019Meta-analyses (Sadeghirad 2014; Fernando 2019) consolidate the observational weight literature and flag that changes are transient and no RCT of the fast exists
- 2016-2021IDF-DAR Diabetes and Ramadan practical guidelines and risk calculator published and updated, formalizing pre-Ramadan risk stratification
- 2025Updated DaR-ADA-IDF Ramadan guidelines and risk calculator announced at the 14th DaR conference, due 2026
- OngoingRecurs annually at population scale; remains a religious obligation studied as a natural model of intermittent fasting
At a glance
- Pattern
- Dawn-sunset, ~30 days
- Includes
- No food or water by day
- Scale
- ~2 billion practitioners
- Research
- Extensive observational base
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Ramadan 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
No RCT of Ramadan fasting exists; weight loss is modest and mostly reversed
Weight and body-composition changes during Ramadan are transient and return to baseline 2-5 weeks after
Lipid shifts during Ramadan are significant but highly heterogeneous with short follow-up
Hypoglycemia risk in type 2 diabetes during Ramadan; sulfonylureas and insulin raise risk; 35 RCTs in this clinical literature
IDF-DAR practical guidelines and pre-Ramadan risk stratification for people with diabetes
International Diabetes Federation, updated DaR-ADA-IDF Ramadan guidelines and risk calculator
Diabetes Management During Ramadan; EPIDIAR found ~79% of type 2 diabetes patients fast; many fast against advice
Endotext, Diabetes Management During Ramadan, NCBI Bookshelf
Meal timing, not the fast alone, drives circadian and cardiometabolic outcomes; late eating misaligns clocks
Scriptural basis and exemptions: fasting prescribed, sick and traveler may make up days, month of revelation
Median 93% of Muslims across 39 countries report fasting during Ramadan; regional variation
Pew Research Center, Most Muslims say they fast during Ramadan
Multi-country observational management and outcomes of type 2 diabetes during Ramadan (CREED)
Babineaux et al., CREED multi-country retrospective observational study, Diabetic Medicine