Eight-hour early versus late eating windows to improve blood sugar and cardiometabolic health in overweight adults

Precise Eating Time to Improve Glycemic Control and Cardiometabolic Health in Prediabetes and Diabetes: the GLYCOTIME Trial

We will try early versus late 8-hour time-restricted eating with moderate calorie reduction to see if it improves blood sugar and heart-related health in adults who are overweight with normal glucose, prediabetes, or non-insulin-treated type 2 diabetes.

Quick facts

• Phase: NA
• Study type: Interventional
• Enrollment: 30 (estimated)
• Ages: 18 Years to 75 Years
• Sex: All
• Sponsor: German Institute of Human Nutrition (other)
• Locations: 1 site (Nuthetal)
• Trial ID: NCT07171281 on ClinicalTrials.gov

What this trial studies

This is a crossover dietary intervention where participants follow two 5-week hypocaloric, 8-hour eating-window diets: one window predominantly in the morning (early TRE) and one predominantly in the afternoon (late TRE). A 10–12 week washout separates the intervention periods to reduce carryover effects. The study measures glucose metabolism and a range of cardiometabolic parameters, and collects biological samples to explore molecular mechanisms. Participants include adults with BMI 25–40 kg/m² who have normal glucose, prediabetes, or type 2 diabetes not treated with insulin.

Who should consider this trial

Good fit: Adults with BMI 25–40 kg/m² who currently eat across at least 12 hours per day and have normal glucose, prediabetes, or non-insulin-treated type 2 diabetes, and who can attend on-site visits.

Not a fit: People on insulin, recent major illness or cardiovascular events, shift workers, pregnant or breastfeeding people, those already practicing time-restricted eating, or those with incompatible medical conditions are unlikely to benefit or be eligible.

Why it matters

Potential benefit: If successful, it could offer a low-cost, medication-free way to improve blood sugar control and reduce cardiometabolic risk by changing when people eat.

How similar studies have performed: Previous time-restricted eating trials have shown weight loss and improvements in some metabolic markers, but direct comparisons of early versus late windows and detailed molecular mechanism data are still limited.

Eligibility criteria

Inclusion Criteria:

* Overweight or obesity (BMI 25-40 kg/m²)
* Healthy glucose metabolism (fasting glucose \<100 mg/dl and glucose after 2 hours OGTT \<140 mg/dl)
* OR impaired glucose metabolism (fasting glucose 100-125 mg/dl and/or glucose after 2 hours OGTT 140-199 mg/dl and/or HbA1c 5.7-6.4%)
* OR type 2 diabetes (according to existing medical diagnosis or fasting glucose \>126 mg/dl and/or glucose after 2 hours OGTT \>200 mg/dl and/or HbA1c ≥6.5%)
* Daily eating window ≥12 hours

Exclusion Criteria:

* Weight changes \> 5% within past 3 months
* Shift work
* Traveling across more than one time zone within one month prior to the study
* Pregnancy and breastfeeding
* Eating disorders, food intolerance/allergy to ingredients in the diet product, vegan diet, practicing time-restricted eating
* Severe chronic illnesses or other conditions that are incompatible with the planned intervention and examination program (e.g. type 1 diabetes, recent cardiovascular event, malabsorption, cancer in the last two years, etc.)
* Treatment with insulin, sulfonylureas, and GLP-1 receptor agonists, steroid use (oral, cutaneous, or parenteral), regular intake of melatonin, anticoagulation treatment that cannot be paused
* Extreme early and extreme late chronotypes

Where this trial is running

Nuthetal

• German Institute of Human Nutrition Potsdam-Rehbruecke — Nuthetal, Germany (RECRUITING)

Study contacts

• Study coordinator: Olga Ramich, Prof. Dr.

Conditions: Prediabetes, Type 2 Diabetes, Obesity &Amp, Overweight, Time-restricted eating, Chrononutrition, Glucose metabolism, Obesity