The Types of Intermittent Fasting, Compared

The common types of intermittent fasting are time-restricted eating (16:8, 14:10, 18:6, one meal a day), whole-day protocols (5:2, 4:3, alternate-day fasting) and religious fasting such as Ramadan. Once calorie intake matches, results look broadly similar, and no trial shows one window beating another. The practical difference is adherence: the schedule you can hold.

What we know, and what we don’t

We know:

• With calories matched, protocols produce similar weight loss. A 4-hour window and a 6-hour window lost the same amount (Cienfuegos et al., Cell Metabolism, 2020). 5:2 matched daily restriction in 107 women over 6 months (Harvie et al., International Journal of Obesity, 2011). Across 99 trials, only alternate-day fasting separated from continuous restriction at all, by −1.29 kg (Semnani-Azad et al., BMJ, 2025).
• Adherence is what separates protocols, not the fasting itself (Catenacci et al., 2025; Trepanowski et al., 2017).
• Real-world retention collapses fast. Of 792,692 fasting-app users, 16.7% were still logging at 13 weeks and 2.1% at 52 (Torres et al., 2022).

We don’t know:

• Whether any single protocol beats another with calories matched. No such trial exists.
• Anything beyond 12 months, for any protocol.
• Whether shorter windows carry unique metabolic effects beyond weight. The one head-to-head window trial found none on its primary outcome.

What are the main types of intermittent fasting?

Three families cover nearly everything people practice. Time-restricted eating confines food to a daily window. Whole-day protocols alternate normal days with heavily restricted ones. Religious fasting, most commonly Ramadan, follows a calendar rather than a health plan. Here’s each protocol against the trials that actually tested it:

Protocol	What it is	Trialled in	Result vs daily restriction	Adherence signal
16:8	8-hour eating window daily	Moro 2016 (trained lifters, 8 weeks); Cienfuegos 2020	Fat mass down, strength held (Moro). Equal to other windows (Cienfuegos)	Most-studied window; typical first choice
14:10	10-hour eating window daily	Wilkinson 2020 (metabolic syndrome, no control group)	Improvements reported, but uncontrolled	Easier to hold; less studied
18:6	6-hour eating window daily	Cienfuegos 2020 (6-hour arm)	Same as the 4-hour window, about 3% weight loss	Stricter; harder than 16:8
OMAD	One meal per day	No calorie-matched trial	Untested at this standard	High social friction; hard to hold long
5:2	Two days a week at about 600-650 kcal	Harvie 2011 (107 women, 6 months)	−6.4 vs −5.6 kg, not significant; greater insulin reduction	Dropout 21% vs 13% on daily restriction
4:3	Three fast days at about 80% restriction, four normal days	Catenacci 2025 (165 adults, 12 months)	−7.7 vs −4.8 kg (P=0.040)	Attrition 19% vs 30% on daily restriction
Alternate-day	Fast every other day	Trepanowski 2017 (100 adults, 12 months)	−6.0% vs −5.3% of body weight, not superior	Dropout 38%, the worst of the big trials
Ramadan	Dawn to dusk, one month	Fernando 2019 (meta-analysis, 2,947 participants)	−1.34 kg (95% CI −1.61 to −1.07), largely regained in 2-5 weeks	Cultural practice, not a weight tool

One naming note, because it trips people up: “4:3” means four normal days and three fast days.

How does time-restricted eating work?

All food lands inside a set daily window, usually 8 to 10 hours, and the hours outside it are water, black coffee and tea. The best window trial randomised 58 adults with obesity (49 completed) to a 4-hour or a 6-hour window for 10 weeks and found the same result in both: roughly 3% of body weight lost, with similar changes in insulin resistance (Cienfuegos et al., 2020). In 34 resistance-trained men, eight weeks of 16:8 with training held constant cut fat mass while strength held (Moro et al., Journal of Translational Medicine, 2016). The same trial also measured lower testosterone and IGF-1 in the fasting group. What that means over months is untested, but it belongs in the row.

How do whole-day protocols work?

Normal eating on most days, heavy restriction on the rest. In the 5:2 trial, two days a week at around 600-650 kcal matched daily restriction on weight (−6.4 vs −5.6 kg, not significant) and did somewhat better on insulin (Harvie et al., 2011). The recent 4:3 trial is the strongest result any fasting protocol has: −7.7 kg against −4.8 kg for daily restriction at 12 months, with fewer people quitting (Catenacci et al., Annals of Internal Medicine, 2025). Alternate-day fasting, the most demanding version, was not superior to daily restriction and lost 38% of its participants (Trepanowski et al., JAMA Internal Medicine, 2017). The pattern across the three is hard to miss: the schedule that fits a normal week keeps its people, and keeping people is where the results come from.

What about Ramadan and other religious fasting?

Ramadan is the most widely practised fasting in the world, and its weight effects are small and mostly temporary. A meta-analysis of 70 publications covering 2,947 people found an average loss of −1.34 kg, largely regained within two to five weeks of the month ending (Fernando et al., Nutrients, 2019). Worth saying plainly: those component studies are mostly observational, since you can’t randomise Ramadan, so the estimate is weaker than the trial numbers above. Religious fasting is practised for its own reasons. It isn’t a weight tool and doesn’t need to be.

Do extended fasts belong in this comparison?

No. Multi-day water fasts sit outside the trial evidence, which covers daily windows and single restricted days. Whatever you’ve read about 72-hour fasts and cellular renewal is running on animal data and enthusiasm. They also carry real risks that the protocols above don’t, which is a clinician conversation, not a blog decision.

Does a shorter window do more?

Not in the one trial that tested it. Four hours and six hours produced the same weight loss and the same metabolic changes (Cienfuegos et al., 2020). There’s no trial behind “benefits by hour” precision, and I’d treat any chart that assigns effects to specific fasting hours as decoration. If a shorter window helps you eat less, that’s a fine reason to use it. It isn’t doing anything extra.

Which intermittent fasting type is best?

The one you can hold for a year. That isn’t a dodge, it’s what the data keeps saying: no trial shows one window beating another once calories match, the trials that find differences find them in adherence, and app-user retention numbers (16.7% at 13 weeks, 2.1% at 52) say quitting is the default outcome. So choose by three practical questions. How many non-eating hours can you actually sustain on a working day? Has the protocol been trialled, or are you the trial? And does it survive your real schedule, dinners, family, shift patterns included? For most people that lands on 14:10 or 16:8, with 4:3 worth a look if whole-day restriction suits you better than daily windows. The evidence hub covers what any of them can realistically deliver.

Key points

• With calories matched, protocols look similar. In Cienfuegos et al. (2020), 4-hour and 6-hour windows produced the same weight loss.
• No matched-calorie head-to-head between two fasting protocols exists. The one recent attempt (Derron et al., Clinical Nutrition, 2025) compared alternate-day fasting with time-restricted eating, but intakes differed (−34% vs −15%), so it can’t rank them.
• Adherence separates protocols. Catenacci et al. (2025): 19% vs 30% attrition. Trepanowski et al. (2017): 38% dropout in the fasting arm.
• Real-world retention is brutal: 16.7% of 792,692 app users still logging at 13 weeks, 2.1% at 52 (Torres et al., 2022).
• Shorter windows show no reliable extra effect (Cienfuegos et al., 2020).
• Religious fasting produces small, temporary change: −1.34 kg, largely regained (Fernando et al., 2019).

Common questions

Is 16:8 better than 5:2?

No trial shows a difference once calories match. Both produced results comparable to daily calorie restriction in their best trials (Cienfuegos et al., 2020; Harvie et al., 2011), and the 2025 BMJ network meta-analysis found no meaningful separation between them. Choose on which one your week can absorb, not on a claimed metabolic edge.

What is 4:3 fasting?

Three fast days a week at about 80% calorie restriction, with four normal days in between. In the one 12-month trial, 165 adults on 4:3 lost 2.9 kg more than the daily-restriction group (P=0.040), and fewer of them quit (Catenacci et al., Annals of Internal Medicine, 2025). It’s currently the strongest trial result any fasting protocol holds.

Does OMAD burn more fat?

Nobody knows, because it has never been tested with matched calories. One meal a day compresses eating hard enough that many people under-eat, which produces weight loss the ordinary way. The claim that it burns more fat than a longer window has no trial behind it.

Which type should a beginner choose?

14:10 or 16:8. They’re the most studied, the least socially disruptive, and the easiest to hold. But the honest answer is whichever schedule you can still be following in a year, because the retention data says that’s the hard part (Torres et al., 2022).

A note on safety

This is general information, not medical advice. If you take medication or have a health condition, talk to your clinician before changing when or what you eat. Whole-day protocols and OMAD are the stricter options here; when fasting isn’t the right tool covers who should skip all of this, and keeping muscle and window timing cover the two questions that usually come next.

References

1. Cienfuegos S, et al. Effects of 4- and 6-h time-restricted feeding on weight and cardiometabolic health. Cell Metabolism. 2020;32(3):366-378.e3. doi:10.1016/j.cmet.2020.06.018
2. Harvie MN, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers. International Journal of Obesity. 2011;35(5):714-727. doi:10.1038/ijo.2010.171
3. Fernando HA, et al. 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:10.3390/nu11020478
4. Moro T, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. Journal of Translational Medicine. 2016;14:290. doi:10.1186/s12967-016-1044-0
5. Catenacci VA, et al. The effect of 4:3 intermittent fasting on weight loss at 12 months. Annals of Internal Medicine. 2025;178(5):634-644. doi:10.7326/ANNALS-24-01631
6. Trepanowski JF, et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults. JAMA Internal Medicine. 2017;177(7):930-938. doi:10.1001/jamainternmed.2017.0936
7. Semnani-Azad Z, et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ. 2025;389:e082007. doi:10.1136/bmj-2024-082007
8. Derron N, et al. Alternate-day fasting elicits larger changes in fat mass than time-restricted eating in adults without obesity: a randomized clinical trial. Clinical Nutrition. 2025;53:212-221. doi:10.1016/j.clnu.2025.08.033
9. Torres L, et al. Retention, fasting patterns, and weight loss with an intermittent fasting app. JMIR mHealth and uHealth. 2022;10(10):e35896. doi:10.2196/35896
10. Wilkinson MJ, et al. Ten-hour time-restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome. Cell Metabolism. 2020;31(1):92-104.e5.
11. Varady KA, et al. Clinical application of intermittent fasting for weight loss: progress and future directions. Nature Reviews Endocrinology. 2022;18(5):309-321. doi:10.1038/s41574-022-00638-x

remain.fit tracks a fasting window, weight and lab markers on one timeline, so you can see whether anything actually moved. The tools observe; the judging is left out.