16:8 Intermittent Fasting: What to Know

What the 16:8 Schedule Means

16:8 means eating all of a day's food within an 8-hour window and fasting for the remaining 16 hours, most commonly by skipping breakfast or dinner. It is one of several named intermittent-fasting schedules; see how to start intermittent fasting for how it compares to 5:2 and alternate-day fasting in the broader research.

Does It Matter When Your 8-Hour Window Is (Early vs. Late)

A 12-week trial in adults with overweight or obesity directly tested this question, comparing an early 8-hour window, a late 8-hour window, a self-selected 8-hour window, and usual-care education. Liver fat, measured by MRI, decreased within all three time-restricted-eating groups but not significantly more than usual care, and did not differ between early, late, or self-selected windows (Dote-Montero et al., 2026) [8]. In other words, in this trial, which 8 hours you choose does not appear to matter as much as whether you keep to a structured window at all; a significantly higher share of the time-restricted groups reached at least 5% weight loss than the usual-care group.

What the Research Shows

Weight and Fat Mass

A 3-month trial in people with obesity and type 2 diabetes found 16:8 fasting, done 3 days a week, produced a larger weight change than control, with improved fasting glucose, HbA1c, and lipids (Sukkriang and Buranapin, 2024) [3]; that protocol ran 3 days a week, not daily, which matters if this trial is cited as evidence for a daily 16:8 schedule. A meta-analysis of 15 trials combining exercise with 16:8 found the combination reduced body weight and fat mass versus exercise alone, with smaller improvements in triglycerides and LDL cholesterol, though the authors caution the evidence base is limited by study number, sample size, and inconsistent participant characteristics (Liu et al., 2026) [7]. Set against that, the largest pooled dataset available, a 2025 network meta-analysis of 99 randomized trials, did not find time-restricted eating beating ordinary calorie restriction; only alternate-day fasting showed that advantage (Semnani-Azad et al., 2025) [1]. Two trials have tested an 8-hour window directly against a calorie-matched comparison, with different results: the longest and largest, 12 months in 139 people with obesity, found no significant weight-loss advantage over calorie restriction alone (net difference -1.8 kg, 95% CI -4.0 to 0.4, p=0.11) (Liu et al., 2022) [11]; a shorter, 14-week trial in 90 adults with obesity found an earlier 8-hour window (7am to 3pm) more effective for weight loss than a wider eating window at the same weight-loss counseling (-2.3 kg, 95% CI -3.7 to -0.9, p=0.002) and improved diastolic blood pressure, though it did not significantly affect fat loss (Jamshed et al., 2022) [12]. A separate, isocaloric trial tested a wider, 10-hour window with most calories eaten before 1 p.m.: over 12 weeks in 41 adults with obesity and prediabetes or diet-controlled type 2 diabetes, it found no significant difference in weight loss between the 10-hour group and a calorie-matched usual eating pattern (average difference 0.3 kg, 95% CI -1.2 to 1.9) (Maruthur et al., 2024) [13]. A post hoc analysis of 39 participants from the same trial found no significant between-group difference in appetite hormones (leptin, ghrelin, adiponectin) or inflammatory markers (CRP, cortisol, sRAGE), though both groups improved on eating-behavior scores; the authors note the analysis was not powered to detect small differences, so the null result should not be read as proof the two patterns are equivalent (Duan et al., 2026) [14].

Lean Mass: The Recurring Caveat

A dedicated, purpose-built 12-week trial testing daily 16:8 against three structured meals a day found no significant weight-loss advantage and a significant reduction in lean mass in the 16:8 group (appendicular lean mass index -0.16 kg per square meter, p=0.005) (Lowe et al., 2020) [2]. This is one of several directly relevant trials for a daily 8-hour-window schedule, not a pooled estimate, and it is the only one of them to report a significant lean-mass reduction; the lean-mass signal is worth taking seriously rather than treating 16:8 as cost-free for muscle, but it was not seen in the other direct trials on this page that reported lean mass.

Resistance Training and Muscle Gain

That caveat is not universal. A 12-week trial in 23 resistance-trained adults deliberately eating a calorie surplus to gain muscle found the 16:8 group had less fat gain and less body-weight gain than an unrestricted control group, while fat-free mass gains and strength gains were similar between groups (Gavanda et al., 2026) [5]. The 16:8 group ate less than its prescribed surplus, which the authors say explains the smaller fat gain, and body composition was measured by single-frequency bioimpedance, so this is not a clean test of the window alone. In this population, actively training and eating a surplus, an 8-hour window did not cost muscle or strength; the lean-mass caveat from the TREAT trial is population- and goal-dependent, not a universal finding.

Liver Fat and Gut Microbiota

See "Does It Matter When Your 8-Hour Window Is" above for the liver-fat trial's findings (Dote-Montero et al., 2026) [8]: time-restricted eating did not reduce liver fat more than usual-care education; the authors link the liver-fat reductions seen in the trial to weight loss and baseline fatty liver rather than to window timing, and note the trial was not powered for secondary outcomes. A structured 8-hour window still helped more participants reach a meaningful weight-loss threshold than usual care.

Cognitive Performance

A small 4-week pilot in 43 healthy women (23 fasting, 20 control) found 16:8 produced a significant BMI reduction versus control, with no significant difference in working memory or attentional-control test performance, and no difference in reported adverse events (McLeod et al., 2026) [6]. This is a small, short pilot; it supports "no evidence of cognitive harm" in this trial, not proof of cognitive benefit or impairment either way.

How 16:8 Compares to Other Schedules

Where 16:8 is compared directly against alternate-day fasting, in a 3-week trial in adults with prediabetes, alternate-day fasting outperformed 16:8 on weight and BMI reduction, though both beat control (Chair et al., 2022) [4]. For the broader comparison across intermittent fasting schedules generally, see how to start intermittent fasting. For the more extreme end of the daily-fasting spectrum, a single daily meal rather than an 8-hour window, see OMAD.

Getting Started

Pay attention to hydration and electrolytes during the fasting window; see electrolytes during a fast for the mechanism and warning signs, without a home dosing recommendation. For what counts as breaking the 16-hour window, see what breaks a fast.

Who Should Talk to a Clinician First

People on insulin, a sulfonylurea, or blood-pressure medication should only start 16:8 under clinician supervision; no 16:8-specific trial in this set tested that population directly, and this is the same standing caution carried from the general intermittent-fasting guide. Pregnancy, a history of an eating disorder, being under 18, and any chronic condition requiring consistent food or medication timing are reasons to get clinician guidance before starting, as a matter of general clinical caution rather than a specific finding from these trials.

Common Questions

Does 16:8 beat other schedules?

Not clearly: the largest pooled estimate available does not show it beating calorie restriction, and a direct comparison found alternate-day fasting ahead of it on weight and BMI (Semnani-Azad et al., 2025 [1]; Chair et al., 2022 [4]).

Does it cost muscle?

That depends on the population and goal: it did in a weight-focused trial and did not in a muscle-gain-focused trial (Lowe et al., 2020 [2]; Gavanda et al., 2026 [5]).

Does the time of day matter?

Not for liver fat in the one trial that tested it directly (Dote-Montero et al., 2026) [8].

Does 16:8 trigger autophagy?

See our page on whether intermittent fasting triggers autophagy for what the human evidence does and does not show.

Authors and Funding of the Cited Studies

• Semnani-Azad et al., 2025 [1]: funded by the Diabetes and Nutrition Study Group of the European Association for the Study of Diabetes, which commissioned the review, and by the Canadian Institutes of Health Research. Of the 22 authors, several reported research funding, honoraria, speaker fees, or advisory-board roles with companies including Novo Nordisk, Eli Lilly, AstraZeneca, Danone, Nestle, General Mills, and multiple food-industry trade groups; all other authors declared no competing interests.
• Lowe et al., 2020 [2]: funded by the University of California, San Francisco's Cardiology Innovations Award Program, the National Institute of Diabetes and Digestive and Kidney Diseases, and the James Peter Read Foundation, with in-kind equipment gifts from iHealth Labs, MOCACARE, and Oura. Dr. Lowe reported personal fees from Keyto outside the submitted work; Dr. Vittinghoff reported personal fees from UCSF during the conduct of the study; Dr. Heymsfield reported personal fees from the Medifast Medical Advisory Board and the Tanita Medical Advisory Board outside the submitted work; Dr. Weiss reported grants from NIH and the James Peter Read Foundation and non-financial support from Mocacare and iHealth Labs during the conduct of the study, is a cofounder and equity stakeholder of Keyto, Inc., and owns stock in and was formerly on the board of Virta, Inc. No other disclosures were reported.
• Sukkriang and Buranapin, 2024 [3]: funded by the Endocrine Society of Thailand, with the article processing charge funded by Chiang Mai University. The authors reported no conflicts of interest.
• Chair et al., 2022 [4]: the authors declared no conflicts of interest, as recorded in the article's PubMed record. A funding statement could not be retrieved for this page.
• Gavanda et al., 2026 [5]: co-author C. Brinkmann (CB in the paper's statement) reported honoraria from Abbott, Lilly, and Novo Nordisk; the paper states that these companies had no role in the study design, data analysis, interpretation, or the decision to publish, and that all other authors report no conflicts of interest (as recorded in the article's PubMed record). A funding statement could not be retrieved for this page.
• McLeod et al., 2026 [6]: funded by the Health Research Council of New Zealand. The paper's competing-interest statement, as recorded in the article's PubMed record, reports that Mei Peng received financial support from the Health Research Council of New Zealand and that the other authors declare no known competing financial interests or personal relationships that could have appeared to influence the work.
• Liu, Hu, and Ma, 2026 [7]: the authors declared that financial support was not received for the work or its publication, and that the work was conducted in the absence of any commercial or financial relationships that could be construed as a conflict of interest.
• Dote-Montero et al., 2026 [8]: the authors declared no conflicts of interest and refer readers to the accompanying ICMJE disclosure forms for further details, as recorded in the article's PubMed record. A funding statement from the published article could not be retrieved for this page; the trial's preprint lists Spanish and European Union public research funders.
• Allaf et al., 2021 [9]: all eight review authors stated they have no conflict of interest. A funding statement for the review's "Sources of support" section could not be retrieved for this page.
• Patikorn et al., 2021 [10]: Dr. Pham reported personal fees for the Southwest Obesity Symposium outside the submitted work; Dr. Varady reported author fees from the Hachette Book Group for her book, The Every Other Day Diet. No other conflicts were reported. A separate funding statement could not be retrieved for this page.
• Liu et al., 2022 [11]: funded by the National Key Research and Development Project, the Outstanding Youths Development Scheme of Nanfang Hospital, the Key-Area Clinical Research Program of Southern Medical University, the Key-Area Research and Development Program of Guangdong Province, and the National Natural Science Foundation of China. The article states that author disclosure forms are available with the full text at NEJM.org but does not print them in the body text; itemized author disclosures were not independently accessible for this page. Participants were also provided one protein shake per day, Nutriease, made by Zhejiang Nutriease, for the first six months, which the paper describes as intended to help adherence to the permitted calorie intake, and the paper's acknowledgments thank three named nutritionists at Zhejiang Nutriease.
• Jamshed et al., 2022 [12]: funded by National Institutes of Health grants, including the National Center for Advancing Translational Sciences and the National Institute of Diabetes and Digestive and Kidney Diseases. Dr. Martin reported grants from NIH during the conduct of the study and personal fees as a scientific advisory board member for Wondr Health outside the submitted work; his institution, Pennington Biomedical Research Center/Louisiana State University, holds an intellectual-property interest in the Remote Food Photography Method and SmartIntake app, on which Dr. Martin is an inventor. Dr. Peterson reported grants from NIH during the conduct of the study. No other disclosures were reported.
• Maruthur et al., 2024 [13]: funded by American Heart Association grants and National Institutes of Health grants. The article refers readers to the authors' ICMJE disclosure forms at acponline.org; itemized disclosures were not accessible for this page.
• Duan et al., 2026 [14]: funded by an American Heart Association grant, with D. Duan separately supported by a National Institutes of Health grant and S. J. Pilla by National Institute of Diabetes and Digestive and Kidney Diseases grants and Resolve to Save Lives. D. Duan reported serving as a consultant for Rhythm Pharmaceuticals and receiving honoraria from the American Diabetes Association; S. Carnell reported receiving grant funding from Eli Lilly and Company; J. M. Clark reported participating on a Data Safety Monitoring Board for Eli Lilly and Company and serving on the advisory board of Novo Nordisk; N. M. Maruthur reported receiving royalties from UpToDate. The other authors declared no conflicts of interest.
• 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. Lean or fat-free mass loss is a recurring but population-dependent signal, not a universal one: it showed up in a weight-focused trial and did not in a muscle-gain-focused trial, so state both rather than only one (Lowe et al., 2020 [2]; Gavanda et al., 2026 [5]). Most of this specific-schedule literature is short, three to twelve weeks in most of the trials reviewed here, though one trial followed participants for 12 months (Liu et al., 2022) [11]; shorter-trial results should not be read as durable or universal. Talk to a clinician before starting if pregnant, under 18, managing diabetes or blood pressure with medication, or with a history of an eating disorder.