Researchers in Iran have launched a clinical trial to test whether time-restricted eating outperforms standard calorie-restricted dieting on measures of circadian rhythm health, sleep quality, and clock gene expression in women with obesity. The 12-week randomized trial, led by investigators at Tabriz University of Medical Sciences and Tehran University of Medical Sciences, will enroll 42 participants and compare a 16:8 intermittent fasting schedule against a conventional energy-restricted diet. The protocol was published on July 18 in the journal Trials.
What they will test
The trial targets two molecular markers that have been linked to circadian disruption in obesity. The first is the clock gene BMAL-1, a core component of the cellular circadian oscillator. BMAL-1 forms a heterodimer with CLOCK to drive the transcription of thousands of genes across virtually every mammalian tissue. In adipose tissue, BMAL-1 expression fluctuates across the day, and animal studies have shown that high-fat feeding blunts the amplitude of its rhythmic oscillation. Obese individuals consistently show reduced BMAL-1 expression compared to lean controls, suggesting that circadian clock disruption is both a consequence of and a contributor to metabolic dysregulation.
The second marker is microRNA-let-7f-1-3p, a small non-coding RNA that regulates metabolic pathways. The let-7 family of microRNAs controls insulin signaling and glucose metabolism by targeting the insulin receptor and multiple components of the PI3K-AKT pathway. Obesity alters the expression of let-7 family members in adipose tissue, and there is emerging evidence that these microRNAs are themselves under circadian control, creating a bidirectional link between clock gene networks and metabolic gene regulation.
In addition to these molecular outcomes, the researchers will assess circadian rhythm status via standardized chronotype and phase questionnaires, sleep quality with the Pittsburgh Sleep Quality Index (PSQI), and a full panel of anthropometric and metabolic markers including weight, body mass index, waist circumference, fasting glucose, lipid profile, and insulin levels. All measurements will be taken at baseline and at the end of the 12-week intervention.
The two diets
The two intervention arms are designed to isolate the effect of meal timing independent of calorie restriction. The time-restricted eating group will follow a 16:8 schedule, consuming all food between 12 p.m. and 8 p.m. each day with no explicit calorie targets. The energy-restricted diet group will consume a calorie-reduced diet composed of 55% carbohydrates, 30% fat, and 15% protein, spread across conventional meal times without any timing restrictions. Both groups will undergo structured dietary evaluation at baseline, mid-study, and at the end of the trial to verify adherence and quantify actual nutrient intake.
The 16:8 schedule was chosen because it creates a daily 16-hour fasting window that aligns the feeding period with the active phase of the central circadian clock. This imposed feeding-fasting cycle functions as a time cue, or zeitgeber, for peripheral circadian oscillators in the liver, adipose tissue, and skeletal muscle. In rodent models, restricting feeding to the active phase can partially restore clock gene expression rhythms that were lost under a high-fat diet, even when total calorie intake remains unchanged.
Why it matters
Obesity and circadian disruption are tightly linked, but the direction of causality has been difficult to establish in humans. Epidemiological studies consistently show that shift workers, who experience chronic circadian misalignment, have higher rates of obesity and metabolic syndrome. Conversely, people with obesity tend to have delayed sleep-wake rhythms and reduced sleep quality, creating a self-reinforcing cycle.
Time-restricted eating has emerged as a promising intervention precisely because it targets the timing of food intake, a behavior that can be modified without requiring patients to count calories, restrict food groups, or follow complex dietary prescriptions. If the trial shows that TRE improves circadian gene expression and sleep quality beyond what calorie restriction alone achieves, it would provide mechanistic support for meal timing as an independent therapeutic target in obesity management. The inclusion of miRNA-let-7f-1-3p adds a novel dimension, as circulating microRNAs are being explored as biomarkers of circadian health and metabolic risk.
The findings will also have practical implications. A dietary intervention that works through circadian mechanisms rather than through calorie restriction alone could be offered to patients who struggle with traditional dieting adherence. If meal timing can be prescribed as a circadian intervention, it would represent a low-cost, scalable strategy that could be integrated into primary care and public health programs for obesity prevention.
Limits
This is a study protocol, not a completed trial. No results have been reported, and the protocol describes only the planned analysis. The sample size of 42 is modest and powered for the primary gene expression outcomes, but it may limit the detection of smaller effects on secondary measures such as sleep quality subscales. The trial is single-center and restricted to women, so generalizability to men or other populations is unknown. Dietary adherence will be self-reported, introducing a potential source of measurement error. The trial is registered on the Iranian Registry of Clinical Trials rather than ClinicalTrials.gov, which may be less familiar to international readers.
Bottom line
This trial is among the first to directly compare time-restricted eating with standard calorie restriction on clock gene expression, miRNA regulation, and sleep quality in human obesity. If the results confirm that meal timing modulates circadian biomarkers independent of caloric intake, it could reshape dietary guidance for metabolic health and provide a clear mechanistic rationale for time-restricted feeding protocols.
Source
Tavakoli A, Kermani N, Zamani P, Pourghassem Gargari B, Dehghan P, Mirzaei K. The effects of time-restricted eating in comparison with energy-restricted diet on expression of BMAL-1 and miRNA-let-7f-1-3p genes, circadian rhythm status, sleep quality, metabolic and anthropometric markers in obese women: a study protocol for a randomized controlled clinical trial. Trials. 2026 Jul 18. doi:10.1186/s13063-026-09905-y. PMID: 42471709.