Alternate-Day Fasting (ADF): The Evidence

What ADF and Modified ADF Mean

Alternate-day fasting (ADF) means eating very little, often 0% to 25% of normal calories, every other day, with normal, ad-lib eating on the days in between. A modified version keeps the every-other-day pattern but allows about 25% of energy needs, often around 500 kilocalories, on fast days. The 5:2 diet is a different pattern: two low-calorie days a week rather than every other day. Both ADF and the 5:2 diet are a different axis from the daily-window schedules covered elsewhere on this site: 16:8 and OMAD restrict the time of day food is eaten, every day, while ADF and 5:2 restrict which days a person eats close to normally. See what is fasting for how these patterns fit the wider landscape of fasting types. Trials of alternate-day fasting as a treatment for a specific diagnosed disease are a separate area and are not summarized here.

Trial-by-Trial Evidence

The table below lists each trial discussed on this page: who was studied, the design and duration, what it found, and what it did not find or could not show, tagged supports, limited evidence, no effect found, or contradicts.

The Core Question: Does ADF Beat Daily Calorie Restriction?

The Longest Trial Cited Here: One Year, Head to Head

The largest and longest trial cited here to test this question directly randomized 100 adults with obesity to ADF (25% of energy needs on fast days, 125% on alternating feast days), daily calorie restriction (75% of energy needs every day), or no intervention, for one year. Weight loss was similar between ADF and daily calorie restriction at both 6 months (-6.8% vs -6.8%, relative to control) and 12 months (-6.0% vs -5.3%, relative to control). Dropout was highest in the ADF group, 38%, compared with 29% on daily calorie restriction and 26% on no intervention. There were no significant between-group differences in blood pressure, heart rate, triglycerides, fasting glucose, fasting insulin, insulin resistance, CRP, or homocysteine. HDL cholesterol rose more on ADF than on daily calorie restriction at month 6 (+6.2 mg/dL, 95% CI 0.1 to 12.4), though not at month 12, while LDL cholesterol was higher on ADF than on daily calorie restriction by month 12 (+11.5 mg/dL, 95% CI 1.9 to 21.1). Participants on ADF ate more than prescribed on fast days and less than prescribed on feast days, a real-world adherence problem specific to the protocol, while the calorie-restriction group generally met its targets. A pre-planned secondary analysis of this same trial found ADF and daily calorie restriction similarly improved the fat-free-mass-to-total-mass ratio and reduced leptin after 24 weeks, with no difference between the two groups (Trepanowski et al., 2018) [16]. The original trial's authors' own conclusion: alternate-day fasting did not produce superior adherence, weight loss, weight maintenance, or cardioprotection compared with daily calorie restriction (Trepanowski et al., 2017) [1].

A Trial Designed to Isolate Fasting From Calorie Reduction

A separate 3-week trial in 36 lean, healthy adults (12 per arm) was built specifically to separate the effect of fasting itself from the effect of eating less. It compared daily calorie restriction (75% of energy daily) against ADF-style restriction that netted the same total calorie deficit (150% of energy every other day), and against ADF with no net energy restriction at all (200% of energy every other day). Total body mass loss did not differ between the matched-restriction ADF arm and daily calorie restriction (-1.60 vs -1.91 kg, P=0.46), but fat loss did: daily calorie restriction reduced body fat by 1.75 kg, while the matched-restriction ADF arm reduced fat by only 0.74 kg, significantly less (p=0.01). The arm with no net energy restriction did not significantly reduce fat mass at all. Postprandial cardiometabolic markers and gut hormones did not differ significantly between groups. The authors' own conclusion: fasting every other day is less effective at reducing body fat than a matched degree of daily energy restriction, with no evidence of a fasting-specific metabolic benefit beyond the calorie deficit itself (Templeman et al., 2021) [2].

Smaller and Shorter Trials

An 8-week pilot trial comparing zero-calorie ADF with daily calorie restriction (-400 kcal/day) in adults with obesity found no adverse effects attributed to ADF and 93% completion, with a larger energy deficit on ADF (376 kcal/day more); there was no significant between-group difference in weight, body composition, lipids, or insulin sensitivity at 8 weeks, and no difference in weight regain after 24 weeks of unsupervised follow-up, though changes from baseline in percent fat mass and lean mass were more favorable with ADF at 24 weeks (Catenacci et al., 2016) [3]. A 12-week trial in normal-weight and overweight adults compared ADF only against a no-intervention control, not against daily calorie restriction, finding weight down 6.5% and fat mass down 3.6 kg relative to control, with no change in fat-free mass; this shows ADF beats doing nothing, a different and much easier bar than beating daily calorie restriction (Varady et al., 2013) [4]. A 4-week trial in healthy, non-obese, middle-aged adults found strict ADF produced a 37% average calorie reduction, improved cardiovascular risk markers, reduced trunk fat mass, and improved (lowered) the fat-to-lean ratio, with no adverse effects reported; it had no daily-calorie-restriction comparison arm, so it cannot address whether ADF beats matched restriction, it carries a 2020 erratum correcting figures from the original paper; 60 people were randomized and 57 completed, and the paper's data on more than 6 months of ADF come from a separate cross-sectional group of 30 people already practising it, not from follow-up of the trial participants (Stekovic et al., 2019) [5]. Fasting-related aging research like this often touches on autophagy, the cell's internal recycling process; see autophagy and fasting for what that process is and what the evidence on it shows. Two trials in adults with metabolic syndrome found modified ADF ahead of daily calorie restriction on weight: an 8-week trial (weight, waist circumference, systolic blood pressure, and fasting glucose all improved more on ADF, with no difference in lipids or HOMA-IR) (Parvaresh et al., 2019) [12], and a 4-month trial from the same research group (weight -6.43 vs -4.11 kg, P=0.02; fat mass -4.88 vs -3.72 kg, P=0.03) (Razavi et al., 2021) [13]; neither has yet been replicated outside that group.

What ADF Does to Weight, Fat Mass, and Lean Mass

Across the trials above, ADF consistently beats no intervention; against daily calorie restriction, the evidence disagrees, as set out above. In an 8-week ADF trial, fat-free mass fell by 1.4 kg of a 3.9 kg total weight loss (Hoddy et al., 2016) [8], while a 12-week ADF-versus-control trial found fat-free mass did not change (Varady et al., 2013) [4], and a pre-planned secondary analysis of the largest trial found ADF and daily calorie restriction similarly improved the fat-free-mass-to-total-mass ratio and reduced leptin, with no difference between groups (Trepanowski et al., 2018) [16]. A meta-analysis of 28 randomized trials spanning ADF, the 5:2 diet, and time-restricted eating found the three patterns combined produced similar body-weight and fat-mass changes to daily calorie restriction, with a slightly greater reduction in fat-free mass and waist circumference, and a pooled body-weight difference of -0.42 kg relative to daily calorie restriction (95% CI -0.96 to 0.13); energy intake was lower in the intermittent-restriction arm than the comparison arm in 5 of the pooled trials and not reported in 6 (Schroor et al., 2024) [7]. ADF specifically improved insulin resistance (HOMA-IR) more than calorie restriction in that same analysis, while the 5:2 diet reduced BMI less than calorie restriction (Schroor et al., 2024) [7].

Blood Pressure, Cholesterol, and Blood Sugar

The largest trial found no significant between-group difference in blood pressure, fasting glucose, fasting insulin, or insulin resistance between ADF and daily calorie restriction. HDL cholesterol rose more on ADF than daily calorie restriction at month 6 (+6.2 mg/dL), though not at month 12, while LDL cholesterol was higher on ADF than daily calorie restriction at one year (+11.5 mg/dL) (Trepanowski et al., 2017) [1]. Anyone managing cholesterol should weigh that specific, trial-documented LDL finding before choosing ADF over a daily calorie-restriction approach.

Hunger on ADF

Two single-group ADF trials with different designs disagree on hunger. One used zero-calorie fast days in 16 non-obese adults, with hunger rated weekly, and found hunger rose on the first fasting day and stayed elevated throughout a 22-day trial, despite no significant change in fasting glucose or ghrelin (Heilbronn et al., 2005) [6]. The other used fast days at 25% of energy needs with food provided, in 59 adults with obesity, rating hunger after meals, and found no increase in subjective hunger by the end of an 8-week trial, even though ghrelin rose; fullness and the satiety hormone PYY increased instead (Hoddy et al., 2016) [8]. The design difference may be one reason the two trials disagree, but this page states both findings rather than resolving the disagreement. A systematic review of 8 studies and 456 participants on ADF and appetite rated the overall evidence low or very low certainty and reached no firm conclusions (Kucuk and Berg, 2022) [17]. See hunger during intermittent fasting for the fuller discussion of hunger and appetite hormones across fasting patterns generally.

Dropout and Real-World Adherence

Dropout was the highest of any group in the largest trial, 38% at one year on ADF versus 29% on daily calorie restriction and 26% on no intervention (Trepanowski et al., 2017) [1]. In the same trial, people assigned to ADF ate more than prescribed on fast days and less than prescribed on feast days, while the calorie-restriction group generally met its targets. Together, these are a concrete sign that the swing between fast and feast days is harder for many people to sustain than a daily pattern.

How ADF Compares to 16:8 and OMAD

ADF, 16:8, and OMAD sit on different axes: ADF varies which days a person eats close to normally, while 16:8 and OMAD restrict the time of day food is eaten, every day. A trial that compared ADF directly against a daily-window schedule, rather than against daily calorie restriction, found ADF reduced weight and BMI more than 16:8 over 3 weeks in adults with prediabetes (Chair et al., 2022) [14]; it is one short trial, not a settled comparison.

Who Should Talk to a Clinician First

Talk to a clinician before trying ADF or modified ADF if you are pregnant, under 18, have a history of an eating disorder, or manage diabetes or blood pressure with medication. People on insulin or other glucose-lowering drugs specifically should be cautious: a fast day alternating with normal eating is a bigger day-to-day swing in intake than daily fasting patterns, and no study cited here directly tests ADF safety in people on glucose-lowering medication; treat this as a gap in the evidence, not a tested finding, and get clinician guidance either way. Anyone managing cholesterol should also raise ADF specifically with a clinician, given the higher LDL cholesterol found on ADF than daily calorie restriction in the largest trial (Trepanowski et al., 2017) [1].

Authors and Funding of the Cited Studies

• Trepanowski et al., 2017 [1]: Krista A. Varady is senior and corresponding author. Disclosure: "Dr Varady reported receiving an advance for the book The Every-Other-Day Diet: The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off, published by Hachette Book Group. No other disclosures were reported." Funding: National Institutes of Health (NHLBI R01HL106228; NIDDK P30DK072476 and F32DK107157).
• Varady et al., 2013 [4]: Varady is first and corresponding author. Disclosure: "The authors have no conflicts of interest to report." Funding: a departmental grant from Kinesiology and Nutrition at the University of Illinois, Chicago.
• Patikorn et al., 2021 [9]: Varady is a co-author; Chaiyakunapruk is corresponding author. Disclosure: "Dr Pham reported receiving personal fees for the Southwest Obesity Symposium outside the submitted work. Dr Varady reported receiving author fees from Hachette Book Group for the book, The Every Other Day Diet. No other conflicts were reported."
• Catenacci et al., 2016 [3]: Disclosure: "No authors have any potential conflicts of interest to disclose." Funding: NIH.
• Stekovic et al., 2019 [5]: the paper's own declaration of interests states, "H.S. received unrestricted research grants from Astra Zeneca, Merck, Sharp & Dhome, and Sanofi-Aventis." H.S. is co-author Harald Sourij, not the paper's first author (Stekovic) or its senior and corresponding author (Madeo).
• Schroor et al., 2024 [7]: Disclosure: "The authors report no conflicts of interest." Funding: no funding was received for this study.
• Elortegui Pascual et al., 2023 [11]: Paloma Elortegui Pascual is first and corresponding author; Krista A. Varady is listed last of the nine authors. Disclosure: "Paloma Elortegui Pascual, Maryann R. Rolands, Alison L. Eldridge, Philipp Gut, Kim Anne Lê, and Fabio Mainardi are employees of Société des Produits Nestlé S.A., a funder of the study. Leonidas G. Karagounis is an employee of Nestlé Health Science, Lausanne, Switzerland. Amira Kassis and Krista A. Varady have received financial support for this project from Société des Produits Nestlé S.A." Funding: Société des Produits Nestlé S.A. and Nestlé Health Sciences, Lausanne, Switzerland.
• Semnani-Azad et al., 2025 [10]: a 22-author paper commissioned and funded by the Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes, with additional funding from the Canadian Institutes of Health Research. Its competing-interests statement is extensive: several co-authors disclose research funding, consulting fees, speaker fees, or advisory-board roles with food and pharmaceutical companies, including Nestlé, Novo Nordisk, and Eli Lilly among others named individually in the paper, and one author's spouse is a former employee of Nestlé Health Science and AB InBev. The remaining authors declare no competing interests.
• Trepanowski et al., 2018 [16] (a secondary analysis of the trial in citation 1): Disclosure: "Krista Varady is the author of the book, 'The Every Other Day Diet', published by Hachette Book Group. The other authors declare no competing interests."
• Disclosures are listed where the full text of the paper was available to us; a study not listed here is not a statement that its authors have no ties.

Safety and Cautions

This is general information, not medical advice. The evidence disagrees on whether alternate-day fasting outperforms daily calorie restriction: pooled analyses and shorter trials show a small edge for ADF, while the longest trial found no advantage, a higher dropout rate, and higher LDL cholesterol on ADF than daily calorie restriction at one year (Trepanowski et al., 2017) [1]. Talk to a clinician before trying ADF or modified ADF if you are pregnant, under 18, have a history of an eating disorder, manage diabetes or blood pressure with medication, or are already managing high cholesterol. Stop and seek care for any severe or concerning symptom.