Ramadan, Lent and Orthodox fasting: faith comes first, safety a close second.
Three traditions, three very different fasts. Here is what religious fasting involves in each, what the research says, and how to stay safe if you have diabetes or another condition.
The short version
- What it is
- Ramadan: no food or drink from dawn to sunset for a lunar month. Orthodox fasting: no meat, dairy or eggs on fast days, up to 180–200 days a year. Catholic Lent: meat-free Fridays and two fast days.
- Good for
- Faith, discipline, community. Side effects in studies: small, temporary weight loss in Ramadan; better cholesterol in Orthodox fasting.
- Bad at
- Being safe on autopilot for people with diabetes, pregnancy or kidney disease. Also: iftar sweets.
- Evidence
- Not rated. These are faith practices, not health diets. Research on Ramadan and Orthodox fasting exists; on Lent, barely any.
- Our take
- Your calendar, your community's rules. We fit the plan around them and flag the safety issues.
What religious fasting actually is
Religious fasting is practised in almost every faith, from Islam and Christianity to Buddhism, Jainism, Hinduism and Judaism.3 This article covers three of the biggest fasts. They share a word, not a rulebook. What is required, and who is excused, is decided by each faith and its scholars and clergy, not by us. Practice also varies between countries, communities and individuals.
Ramadan
Fasting in Ramadan is one of the five pillars of Islam and is obligatory for healthy Muslims from puberty.2 For 29 or 30 days, Muslims who fast take no food and no drink, not even water, from dawn to sunset. Most eat one bigger meal after sunset (iftar) and a lighter one before dawn (suhoor).3 The Islamic calendar is lunar, so Ramadan moves through the seasons, and the length of the fast depends on where you live. In northern Britain daylight lasts under 6 hours in winter and about 19 in midsummer.3 Near the equator, in Singapore, the fast stays roughly the same length all year.
Orthodox fasting
The Eastern Orthodox Church sets out a kind of periodic vegetarianism: on fast days, no meat, dairy or eggs, for a total of around 180–200 days a year.4 The main periods are about 40 days before Christmas, 48 days before Easter (Great Lent), two weeks in August before the Dormition, the Apostles' fast in early summer, plus most Wednesdays and Fridays.3 Seafood such as octopus, squid and prawns is generally allowed; fish only on certain days.3
Catholic Lent
For Roman Catholics, every Friday and the season of Lent are times of penance. Catholics abstain from meat on Fridays, and fast and abstain on Ash Wednesday and Good Friday. Each national bishops' conference decides the details, and can swap abstinence for other acts such as charity.5 In many countries "fasting" means one full meal and two small ones.
How it works in your body
Ramadan is a daily dry fast followed by night-time eating. In plain terms, it's time-restricted eating with the window moved to the night and no water during the day. Your body runs on stored sugar and then fat through the afternoon, and you rehydrate after sunset. Studies show people tend to drink less overall during Ramadan, which is why hot, long days are harder.3
Orthodox fasting isn't a fast in the no-food sense. It's a switch, many times a year, between normal eating and a mostly plant-based diet close to the Mediterranean pattern. In a year-long study in Crete, people who fasted ate less saturated fat and about 180 kcal a day less at the end of fasting periods, plus more fibre and folate, but also less calcium.9
Catholic Lent rules are light by comparison: meat-free days and two reduced-food days. Their direct effect on the body is small.
What you eat, what you don't
Eat
- Ramadan: halal food and plenty of water between sunset and dawn
- Ramadan suhoor: protein, wholegrains, fruit and water to carry you through the day
- Orthodox fast days: vegetables, legumes, grains, fruit, nuts, olives, seafood such as octopus, squid and prawns
- Catholic meat-free days: fish, eggs, dairy, vegetables, legumes
Not eaten
- Ramadan: no food or drink from dawn to sunset
- For Muslims at all times: pork and alcohol (see halal)
- Orthodox fast days: meat, dairy, eggs, and fish on most fast days
- Catholic Fridays in Lent, Ash Wednesday and Good Friday: meat
- Catholic Ash Wednesday and Good Friday: full meals beyond the one allowed
The Orthodox fast-day pattern is close to vegan plus seafood. If you're curious about other faith-based fasts, the Daniel Fast is a 21-day plant-based fast from the Christian tradition.
Alcohol during religious fasts
Islam prohibits intoxicants at all times, not just in Ramadan.13 During the fast itself, nothing passes the lips anyway.
Catholic canon law sets rules on meat and fasting, not on alcohol, so giving up drink for Lent is a personal choice.5 Orthodox guidance on wine during fasts varies between churches and parishes, so ask your priest. If you do drink, our alcohol guide covers what to know.
What the research says
Ramadan and weight: a dip, then a rebound
A meta-analysis of 70 studies with nearly 3,000 healthy adults found weight and body fat dropped during Ramadan, especially in people with overweight or obesity. Within two to five weeks after Ramadan, the numbers drifted back towards where they started.7 Some muscle went too, though less than fat.7
Orthodox fasting and cholesterol
A systematic review of 10 studies, almost all from Greece, found Orthodox fasting periods consistently lowered total and LDL ("bad") cholesterol, by up to about 18% and 31%. The effect on HDL, weight and blood sugar was unclear.83 Iron, a common worry with plant-based eating, held up fine in a study of strict fasters over the 40-day Christmas fast.10
Lent
We found no solid studies on the health effects of Catholic Lenten practice. That's not a criticism: Lenten practice is about penance and prayer, not health outcomes.
The uncomfortable truth
"Ramadan is a great way to lose weight." It isn't designed to be one, and the data agree: the weight mostly comes back within weeks.7 Some people even gain, when iftar turns into a nightly feast of fried food and sweets.3 Ramadan is a spiritual practice. The food industry's Ramadan promotions, with their sugar-loaded drinks and pastries, are not.
"All fasting is the same." No. Ramadan is a dry fast: no water. Our own fasting rule allows water, black coffee and green tea. Orthodox fasting is mostly about which foods, not whether you eat. Mixing up the rules, or stacking an app's fasting plan on top of a religious fast, is how people end up dizzy and dehydrated.
The risks
- Diabetes and low blood sugar. In a study of over 12,000 people with diabetes in 13 countries, severe hypoglycaemia was several times more common during Ramadan than in other months, and more common in people who changed their medication dose or activity level.11 The International Diabetes Federation and the DaR International Alliance publish guidelines for people with diabetes who choose to fast.2 On insulin, sulfonylureas or SGLT2 drugs, see your doctor before Ramadan, not during it.
- Dehydration. No water for up to 19 hours in a northern summer, and people drink less overall.3 Kidney disease, heat and physical work all make it riskier.
- The iftar sugar rush. In one study, people ate more sweets and drank more sugary drinks during Ramadan than the rest of the year.3
- Calcium, vitamin D and B12 in Orthodox fasting. Months without dairy, eggs and meat can leave these short. Researchers flag it as an open question.89
- Pregnancy. Pregnant women are exempt from the Ramadan fast, yet many fast anyway. A review found no effect on birth weight but not enough data on other outcomes.12
- Eating disorders. Any fasting practice can be hijacked by an eating disorder. If fasting feels like control rather than faith, talk to someone.
Who is excused, as each tradition defines it
Islam: the Qur'an allows those who are ill or travelling to make up missed days later, and those for whom fasting is extremely hard to feed a needy person for each day instead.1 Pregnant women are exempt.12 Many people with diabetes and serious illness are too.2 The details are for your imam or scholar.
Catholic Church: abstinence from meat applies from age 14; fasting applies to adults, from 18, until the start of their 60th year.56 A parish priest can excuse or change the obligation for a just cause.5
Orthodox churches: how strictly to fast, and allowances for illness, pregnancy, children or old age, are usually agreed with your priest or spiritual father.
Allergies: watch the staples
Fasting menus lean on some of the EU's 14 major allergens. If you're allergic, the plan swaps them within your tradition's rules.
| Staple | Allergen (EU list of 14)14 | Swap |
|---|---|---|
| Samosas, bread, pastries at iftar | Cereals containing gluten | Rice, lentil soup |
| Hummus, tahini, halva | Sesame | Bean dips with olive oil |
| Nut-filled sweets, walnuts in Lenten dishes | Tree nuts | Pumpkin or sunflower seeds |
| Octopus, squid, mussels | Molluscs | Beans, chickpeas |
| Prawns, shrimp | Crustaceans | Beans, tofu (if soy is fine) |
| Friday fish | Fish | Eggs, cheese, legumes |
| Yoghurt and milk drinks at suhoor | Milk | Fortified soy or oat drink |
Talk to your doctor, and your imam or priest, before fasting if you…
- have diabetes, especially on insulin, sulfonylureas or SGLT2 drugs
- are pregnant or breastfeeding
- have kidney disease or heart disease
- take medication that has to be taken with food or at set times
- have ever had an eating disorder, or are underweight
- are under 18
Healthen me asks about all of these and gives you a different plan if any apply. Whether you fast is your decision with your faith community. Doing it safely is a job for you and your doctor.
How we use religious fasting in your plan
Religious fasting is a filter that follows your calendar. Tell Healthen me which tradition you follow and the plan adapts on the right days.
Ramadan: the religious fast replaces our fasting rules for the month. Your eating window becomes the time between iftar and suhoor, and we don't add our own fasting on top: no Rebel Day fasting either. Break the fast the way your tradition and family do, then the plan suggests protein, vegetables and water before the sweets, and a suhoor that keeps you going: protein, wholegrains, fruit, water.
Orthodox fast days: meals switch to plant-based plus seafood, with an eye on calcium and B12.
Catholic Lent: Fridays go meat-free, and Ash Wednesday and Good Friday get lighter meals.
If Healthen me screens you out of fasting for medical reasons, we don't tell you whether to keep a religious fast. That's between you, your doctor and your faith community. We'll point you to the doctor first. Questions about what your tradition requires, or whether a product is permitted, are for your community, not our app.
This article is general information, not medical advice. If you have a medical condition or take medication, talk to your doctor before changing how you eat.
Sources
- The Qur'an, 2:184. Translation: Khattab M, The Clear Quran. quran.com/2/184
- Hassanein M et al. Diabetes and Ramadan: practical guidelines 2021. Diabetes Research and Clinical Practice 2022;185:109185. doi.org/10.1016/j.diabres.2021.109185
- Trabelsi K et al. Religious fasting and its impacts on individual, public, and planetary health: fasting as a "religious health asset" for a healthier, more equitable, and sustainable society. Frontiers in Nutrition 2022;9:1036496. doi.org/10.3389/fnut.2022.1036496
- Lazarou C, Matalas AL. A critical review of current evidence, perspectives and research implications of diet-related traditions of the Eastern Christian Orthodox Church on dietary intakes and health consequences. International Journal of Food Sciences and Nutrition 2010;61(7):739–758. pubmed.ncbi.nlm.nih.gov/20459365
- Code of Canon Law, canons 1244–1253 (days of penance, fasting and abstinence). Holy See. vatican.va
- Code of Canon Law, canon 97 (age of majority). Holy See. vatican.va
- Fernando HA, Zibellini J, Harris RA, Seimon RV, Sainsbury A. Effect of Ramadan fasting on weight and body composition in healthy non-athlete adults: a systematic review and meta-analysis. Nutrients 2019;11(2):478. doi.org/10.3390/nu11020478
- Koufakis T et al. Effects of Orthodox religious fasting on human health: a systematic review. European Journal of Nutrition 2017;56(8):2439–2455. pubmed.ncbi.nlm.nih.gov/28856433
- Sarri KO, Linardakis MK, Bervanaki FN, Tzanakis NE, Kafatos AG. Greek Orthodox fasting rituals: a hidden characteristic of the Mediterranean diet of Crete. British Journal of Nutrition 2004;92(2):277–284. pubmed.ncbi.nlm.nih.gov/15333159
- Sarri KO, Kafatos AG, Higgins S. Is religious fasting related to iron status in Greek Orthodox Christians? British Journal of Nutrition 2005;94(2):198–203. pubmed.ncbi.nlm.nih.gov/16115353
- Salti I et al. A population-based study of diabetes and its characteristics during the fasting month of Ramadan in 13 countries: results of the EPIDIAR study. Diabetes Care 2004;27(10):2306–2311. doi.org/10.2337/diacare.27.10.2306
- Glazier JD et al. The effect of Ramadan fasting during pregnancy on perinatal outcomes: a systematic review and meta-analysis. BMC Pregnancy and Childbirth 2018;18:421. doi.org/10.1186/s12884-018-2048-y
- The Qur'an, 5:90. Translation: Khattab M, The Clear Quran. quran.com/5/90
- Regulation (EU) No 1169/2011 on food information to consumers, Annex II (the 14 allergens). eur-lex.europa.eu/eli/reg/2011/1169/oj