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Early time-restricted eating and daytime bright light therapy may improve glycemic control in adults with type 2 diabetes

This protocol describes a 4-arm randomized controlled trial testing the independent and combined effects of early time-restricted eating (eTRE) and daytime bright light therapy (BLT) on glycemic control and other health outcomes in adults with type 2 diabetes. The trial will randomize 344 participants to one of four groups: control, eTRE, BLT, or eTRE+BLT, with an intensive 16-week intervention and follow-up at 1 year. The primary outcome is glycemic control measured by HbA1c and 24-hour glucose.

Last updated: Aug 25, 2026•1 RCTs•📖 Read as article →

Evidence Score

Evidence Score42/100
Human RCT★★☆☆☆
Meta-analysis☆☆☆☆☆
Mechanism★★★★★
Safety★★★★☆
Confidencelow

Study Evidence

Study 1. Protocol for the CLOCKS study: A 4-arm randomized controlled trial testing the independent and combined effects of 2 chronotherapies-early time-restricted eating and daytime bright light therapy-in adults with type 2 diabetes.

observational

Steger FL, Salvy SJ, Vaughan TB, Lowry C, Richman JS, Gamble KL, Garvey WT, Scheer FAJL, Peterson CM · Nutrition research (New York, N.Y.) (2026)

Participants: N/A
Duration: 16 weeks (intensive phase), follow-up at 1 year
Intervention: Early time-restricted eating (8-hour eating window ending by 17:00) and/or daytime bright light therapy (90 min/day before 15:00) with blue-light-blocking glasses and blackout curtains at night
Outcome: Glycemic control (HbA1c, 24-hour glucose), diurnal melatonin and cortisol rhythms, diurnal variation in glucose uptake, body mass, body composition, resting energy expenditure, cardiovascular risk factors, sleep parameters, quality of life, psychological health
Effect Size: N/A
Population: Adults with insulin-independent type 2 diabetes

Result:

PubMed: 42594524DOI: 10.1016/j.nutres.2026.07.006

Mechanism Graph

Eating earlier in the day aligns food intake with circadian rhythms, improving glucose metabolism
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Daytime bright light exposure strengthens circadian rhythms, enhancing melatonin and cortisol rhythms
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Optimized circadian rhythms improve insulin sensitivity and glucose uptake
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Result: Improved glycemic control and cardiometabolic health

Limitations

  • ⚠This is a protocol paper, so results are not yet available; efficacy is not established
  • ⚠The intervention requires significant participant adherence (e.g., strict eating window, daily light therapy) which may affect feasibility and generalizability
  • ⚠The study population is limited to insulin-independent T2D, so findings may not apply to insulin-dependent patients

Frequently Asked Questions

What is early time-restricted eating (eTRE)?▼

eTRE is a form of intermittent fasting where all food is consumed within an 8-hour window that ends by 17:00 (5 PM).

What is daytime bright light therapy?▼

Daytime bright light therapy involves exposure to bright light for 90 minutes before 15:00 (3 PM) to strengthen circadian rhythms, combined with avoiding blue light at night.

What is the primary outcome of the CLOCKS study?▼

The primary outcome is glycemic control, measured by HbA1c and 24-hour glucose levels.

How long is the intervention period?▼

The intensive phase lasts 16 weeks, with a follow-up assessment at the 1-year mark.

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References

  1. 1.Steger FL, Salvy SJ, Vaughan TB, Lowry C, Richman JS, Gamble KL, Garvey WT, Scheer FAJL, Peterson CM. "Protocol for the CLOCKS study: A 4-arm randomized controlled trial testing the independent and combined effects of 2 chronotherapies-early time-restricted eating and daytime bright light therapy-in adults with type 2 diabetes.." Nutrition research (New York, N.Y.), 2026. PMID: 42594524 DOI: 10.1016/j.nutres.2026.07.006
Disclaimer: This content is for educational purposes only and is not medical advice. Evidence scores reflect the quality and quantity of available research, not clinical recommendations. Always consult a healthcare professional before starting any supplement or intervention.