Protocol
Time-Restricted Eating (TRE)
One small randomized crossover A trial design in which each participant receives both the treatment and the comparison, one after the other, and serves as their own control. trial (8 men with prediabetes) found early time-restricted feeding improved insulin sensitivity and blood pressure under controlled feeding.
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How this letter has changedLatest: October 2026 · Downgraded.
Time-restricted eating held a B on the claim that its trials isolate a timing effect independent of calories. One of the two trials cited, Wilkinson et al. (Cell Metab 2020; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 31813824), is single-arm with no control group. The other, Sutton et al. (Cell Metab 2018; PMID 29754952), is a crossover in 8 men. The larger randomized trials that matched calories found no added effect of the eating window: Liu et al. (N Engl J Med 2022; PMID 35443107; 139 adults, 12 months) and Lin et al. (Ann Intern Med 2023; PMID 37364268; 90 adults, 12 months). One small positive trial without replication The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away. is C, and the isocaloric-timing claim is withdrawn. Editor adjudication, October 2026.PMID 29754952 PMID 31813824 PMID 35443107 PMID 37364268
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Time-restricted eating means eating all of the day's food in a set window, such as 8 hours. People who do it often lose some weight. That is mainly because they eat less. When studies compared it with eating the same smaller amount at any time of day, the window added nothing extra. Some people also lost a little muscle. It carries risks for people with a past eating disorder, in pregnancy, and for people using insulin, whose blood sugar can drop too low.
Dietary protocol · Metabolic health
Why this gradeGrade C, small or unreplicated trials. The reasoning, and what the grade does not cover.
Grade C. One small randomized crossover (Sutton 2018, 8 men) found metabolic improvement with calories held equal; the second trial previously cited (Wilkinson 2020) is single-arm with no control group and cannot replicate it. When calories were matched in larger randomized trials, adding an eating-time window added nothing: Liu 2022 (139 adults, 12 months) and Lin 2023 (90 adults, 12 months). Surrogate endpoints A lab value or measurement used in place of the outcome that matters, such as LDL cholesterol standing in for heart attacks. Moving a surrogate does not always move the outcome. only; no hard-outcome data. Moved from B in October 2026 by editor adjudication. The earlier basis, that the trials isolate a timing effect independent of calories, is withdrawn because the larger calorie-matched trials do not show one. Wang et al. (BMC Geriatr, 2025; PMID 41310471) is a positive randomized pilot on a cognitive endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. in mild cognitive impairment, but n=46 at a single site against an untreated control, and it does not bear on the metabolic claim. Hu et al. (Eur J Clin Nutr, 2026; PMID 42538400) followed 31,044 NHANES adults and found a last meal before 19:00 carried higher all-cause mortality than one between 19:00 and 20:00 (HR 1.13); it is observational Research that watches what people already do rather than assigning a treatment. It can show that two things travel together, not that one causes the other. and cannot move a grade, but a reader following an early window is entitled to know it exists.
A grade describes the human evidence for a named use. It is not advice, and it is not a judgment on any individual prescription. How the letters are decided →
Time-restricted eating confines food intake to a consistent 6 to 10 hour window each day, extending the overnight fast. One small randomized crossover trial found better insulin sensitivity and blood pressure with early time-restricted feeding when calories were held equal. The larger randomized trials that matched calories found no added benefit from the eating window, so the benefits seen elsewhere are likely to come from eating less. Grade C reflects one small positive trial on surrogate markers, not replicated, with no hard mortality or morbidity endpoint data.
| Common protocols | 16:8 (16 hours fasted, 8 hour eating window). 14:10 (most studied in women). 18:6 (higher adherence difficulty). The eating window should be aligned with daylight hours: earlier is better (10am to 6pm outperforms 12pm to 8pm in circadian alignment studies). |
| Best evidence window | 8 to 10 hour eating window starting before noon. Early time-restricted eating (eTRE) has the strongest metabolic evidence due to circadian alignment with insulin sensitivity patterns. |
| Who benefits most | Adults with overweight, insulin resistance, or metabolic syndrome. Lean healthy adults show smaller measurable effects. Not appropriate for people with history of eating disorders or underweight individuals. |
| Caloric restriction caveat | Many TRE trials show weight loss alongside metabolic improvements. It is not fully established whether the metabolic benefits are from the fasting itself or from the caloric reduction it produces. Some isocaloric TRE trials still show benefits suggesting a fasting-independent effect. |
| Protein preservation | Adequate protein intake (1.6 to 2.2g/kg/day) during the eating window is essential to prevent lean mass loss. TRE without adequate protein can cause muscle loss, particularly in older adults. |
Fasting glucose and insulin (HOMA-IR) at baseline and 12 weeks. HbA1c A blood test that reflects average blood sugar over the previous two to three months. if diabetic or prediabetic. Blood pressure. Body weight and waist circumference. CGM to see glucose variability response to TRE. A simple log captures eating window consistency.
5-week crossover RCT in 8 men with metabolic syndrome. Early time-restricted eating (6-hour window, eating before 3pm) significantly reduced insulin levels, blood pressure, and oxidative stress compared to a 12-hour eating window, without caloric restriction. This isocaloric design established fasting-independent metabolic benefits.
Lowe 2020 (TREAT; PMID 32986097): 116 adults with overweight, 16:8 eating window against three meals a day for 12 weeks; weight loss did not differ between groups. Liu 2022 (PMID 35443107): 139 adults with obesity, all on the same calorie target for 12 months, with or without an 8-hour eating window; weight, body fat and metabolic markers did not differ. In both, the eating window added nothing beyond the calories eaten.
Pilot RCT of 19 adults with metabolic syndrome. A 10-hour eating window for 12 weeks significantly reduced weight, blood pressure, LDL-C Low-density lipoprotein cholesterol, the cholesterol fraction most closely tied to plaque in the arteries., and HbA1c without prescribed caloric restriction. 70 percent of participants maintained weight loss at 12-month follow-up.
TRE is generally safe for healthy adults. Contraindicated in people with a history of eating disorders or eating disorder risk factors, in pregnancy or breastfeeding, in type 1 diabetes on insulin (hypoglycemia risk), and in underweight individuals. People on medications requiring food (metformin, certain blood pressure medications) need to adjust timing.
Metformin should be taken with food, adjust timing to within the eating window. Medications that lower blood sugar require monitoring during extended fasting periods. NSAIDs and aspirin should be taken with food to reduce GI irritation. Thyroid medications (levothyroxine) are typically taken on an empty stomach. This is compatible with morning fasting if taken before the eating window opens.
TRE is one of the most practical dietary interventions because it requires no calorie counting, no food restriction, and no special foods. The primary requirement is consistency of the eating window. The windows studied in the circadian-alignment trials are earlier ones, roughly 10 hours aligned with daylight, for example 9am to 7pm. Late windows that push the first meal well past morning run against that literature rather than with it.
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Primary evidenceFive papers, each linked to its PubMed record.
Sutton et al. (Cell Metab, 2018; PMID 29754952): randomized crossover trial, 8 men with prediabetes, early time-restricted feeding with calories matched; insulin sensitivity and blood pressure improved. Wilkinson et al. (Cell Metab, 2020; PMID 31813824): single-arm study of 10-hour time-restricted eating in 19 adults with metabolic syndrome, with no control group; weight and cardiometabolic markers fell. Liu et al. (N Engl J Med, 2022; PMID 35443107): randomized trial, 139 adults with obesity, 12 months, time-restricted eating plus calorie restriction against the same calorie restriction alone; no difference in weight, body fat, blood pressure or metabolic risk factors. Lin et al. (Ann Intern Med, 2023; PMID 37364268): randomized trial, 90 adults with obesity, 12 months; time-restricted eating and calorie restriction both reduced weight against control, with no difference between them. Wang et al. (BMC Geriatr, 2025; PMID 41310471): assessor-blinded pilot randomized trial, 46 adults with mild cognitive impairment in Chengdu, mean age 74, 12 weeks of a 15:9 window against ad libitum eating; MoCA and AVLT-H recognition, both pre-specified primary outcomes, improved at 6 and 12 weeks.
These statements have not been evaluated by the Food and Drug Administration. Any grade on this page describes the strength of published human trial evidence in the populations studied. It is not a recommendation for any individual and is not medical advice. Starting, stopping or changing any supplement or medication is a decision for your physician.
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("time-restricted eating"[tiab] OR "time-restricted feeding"[tiab]) AND (calorie restriction[tiab] OR caloric restriction[tiab]) AND randomized controlled trial[pt]Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →