Time-Restricted Eating and Personalized Energy-Restricted Diet in Obese Postmenopausal Women

Study Setting, Timing, and Sample

This study is a quasi-randomized, controlled, open-label, parallel-group intervention study. The coordinating center is the Department of Internal Medicine, Faculty of Medicine, Gazi University, and the study will be conducted among postmenopausal women attending the Internal Medicine Outpatient Clinic of Cihanbeyli State Hospital in Konya, Türkiye, who meet the eligibility criteria and agree to participate in the study.

The study will compare the effects of time-restricted eating and a personalized energy-restricted diet on anthropometric measurements, body composition, handgrip strength, blood pressure, biochemical parameters, sleep quality, and menopausal symptoms.

The sample size was determined based on changes in body weight reported in studies evaluating a personalized energy-restricted diet and time-restricted eating in postmenopausal women. Based on these values, the calculated effect size was Cohen's d = 1.13. A power analysis was performed using G*Power 3.1.9.7 based on a two-tailed independent-samples t-test. With an alpha level of 0.05, statistical power of 0.85, and an effect size of 1.13, a minimum of 16 participants per group, corresponding to 32 participants in total, was required to achieve adequate statistical power (actual power = 0.85). Considering an anticipated 20% participant loss, a total of 40 participants, with 20 participants in each group, will be recruited.

Participant recruitment is planned between November 1, 2026 and August 1, 2027.

Eligible individuals will be informed in detail about the study, and written informed consent will be obtained from those who agree to participate.

Study Design and Group Allocation

The study is designed as a quasi-randomized, controlled, open-label, parallel-group intervention study. Participants will be stratified according to age (<55 and ≥55 years) and body mass index (BMI; <35 and ≥35 kg/m²), and stratified blocks will be created. Within these strata, a web-based randomization program (Random.org) will be used to determine the initial allocation of participants to the intervention or control group.

The stratified blocks will be created to minimize potential differences in age and BMI between the intervention and control groups.

After the allocation is communicated, participants who do not wish to follow the assigned dietary intervention may request participation in the other dietary group. Such requests may be accommodated depending on the number of participants in each group. If the requested change cannot be accommodated because of group size limitations, the participant will be withdrawn from the study.

Because of the nature of the dietary interventions, neither the participants nor the researchers can be blinded to group assignment.

General Study Plan

The study consists of an initial assessment and a 12-week intervention period.

Initial Assessment and Pre-Visit Conditions

Before the intervention, participants will undergo a comprehensive baseline assessment. Height, body weight, waist circumference, and hip circumference will be measured, and BMI and waist-to-height ratio will be calculated.

Body composition, including fat-free mass, fat mass, muscle mass, and body water, will be assessed using a Tanita DC 360 bioelectrical impedance analysis device.

Nutritional status will be assessed using a 3-day dietary record, including two weekdays and one weekend day. Physical activity level will be assessed using two 24-hour physical activity records, including one weekday and one weekend day.

Handgrip strength will be measured using an electronic hand dynamometer. Blood pressure will be measured, and fasting venous blood samples will be collected for biochemical analyses. Menopausal symptoms will be assessed using the Menopause Rating Scale, and sleep quality will be assessed using the Pittsburgh Sleep Quality Index.

Participants will be instructed regarding the conditions required before measurements. For biochemical analyses, blood samples will be collected in the morning after at least 10 hours of fasting. Participants who do not meet the required fasting conditions will be asked to attend the study site in the morning after completing the required fasting period without consuming food or beverages.

Intervention Group: Time-Restricted Eating

Participants assigned to the intervention group will receive general healthy eating recommendations for the postmenopausal period and will be instructed to follow a time-restricted eating schedule for 12 weeks. Participants will consume food within an 8-hour daily eating window and fast for 16 hours.

The starting time of the eating window will be selected by the participant between 08:00 and 12:00. During the 16-hour fasting period, water, unsweetened tea, plain coffee, and plain mineral water will be permitted.

No additional energy restriction will be prescribed in the time-restricted eating group.

Control Group: Personalized Energy-Restricted Diet

Participants assigned to the control group will receive general healthy eating recommendations for the postmenopausal period and will follow a personalized energy-restricted diet for 12 weeks. The diet will be planned in accordance with the dietary recommendations provided in the guidelines of national and international menopause societies, while also considering individual dietary preferences.

Energy requirements will be estimated using the Mifflin-St Jeor equation, and the prescribed diet will provide approximately 25% less energy than the estimated daily energy requirement.

Participants will be advised to consume three main meals, consisting of breakfast between 08:00 and 10:00, lunch between 12:00 and 13:00, and dinner between 18:00 and 19:00, with one to three snacks according to individual needs.

Follow-up and Monitoring

Dietary adherence and dietary intake will be monitored every 2 weeks using dietary records. Participants will be invited to the Dietitian Clinic of Cihanbeyli State Hospital for follow-up.

Anthropometric measurements, blood pressure, and handgrip strength will be assessed every 4 weeks during the intervention. Thus, these measurements will be performed at baseline and at weeks 4, 8, and 12.

At the end of the 12-week intervention, baseline assessments will be repeated. Menopausal symptoms and sleep quality will be reassessed during the study, whereas diet satisfaction will be assessed once at the end of the study. A 3-day dietary record and two 24-hour physical activity records will be obtained, and anthropometric measurements, body composition, handgrip strength, blood pressure, and biochemical parameters will be reassessed.

Anthropometric Measurements

Anthropometric measurements will be performed by the study dietitian.

Body weight: Body weight will be measured barefoot and wearing light clothing using a Tanita DC 360 body composition analyzer.

Height: Height will be measured using a F. BOSCH wall-mounted stadiometer, with the participant standing with the feet together and the head positioned in the Frankfurt horizontal plane.

Body mass index: BMI will be calculated as body weight in kilograms divided by height in meters squared and will be evaluated according to WHO criteria.

Waist circumference: Waist circumference will be measured in centimeters at the midpoint between the lowest rib and the iliac crest using a non-stretchable, flexible fiberglass measuring tape.

Hip circumference: Hip circumference will be measured at the widest point of the hips using a non-stretchable, flexible fiberglass measuring tape.

Waist-to-height ratio: Waist-to-height ratio will be calculated by dividing waist circumference by height and will be evaluated according to the Ashwell classification.

Waist-to-hip ratio: Waist-to-hip ratio will be calculated by dividing waist circumference by hip circumference.

Assessment of Body Composition

Body composition will be assessed by the study dietitian using a Tanita DC 360 bioelectrical impedance analysis device. Fat-free mass, fat mass, muscle mass, body water, and visceral fat level will be obtained.

Measurements will be performed in the morning under standardized conditions. Participants will be instructed to avoid strenuous physical activity for 48 hours before the measurement, refrain from eating for at least 4 hours before the test, avoid excessive fluid intake before the measurement, avoid tea and coffee for 4 hours before the measurement, and remove metal objects that may come into contact with the body during the assessment.

Handgrip Strength

Handgrip strength will be measured by the study dietitian using an electronic hand dynamometer (DEMPOWER DP434). One measurement will be obtained from each hand, and the mean of the two measurements will be used for analysis. Handgrip strength below 16 kg will be classified as low muscle strength.

Assessment of Dietary Intake

Nutritional intake will initially be assessed using a 3-day dietary record consisting of two weekdays and one weekend day. Reported food and beverage quantities will be converted into standard amounts by the researcher. Energy, macronutrient, and micronutrient intakes will be analyzed using the Computer-Assisted Nutrition Program, Nutrition Information Systems Package Program (BEBIS).

Dietary intake will be monitored every 2 weeks during the intervention to assess dietary adherence.

Assessment of Physical Activity

Physical activity will be assessed using two 24-hour physical activity records, consisting of one weekday and one weekend day. The duration of sleep, lying, sedentary activities, and light, moderate, and vigorous activities during a 24-hour period will be recorded.

Total energy expenditure will be calculated by multiplying the duration of each activity by the corresponding physical activity ratio (PAR). Physical activity level (PAL) will be calculated by dividing total energy expenditure by 24 hours.

Assessment of Menopausal Symptoms

Menopausal symptoms will be assessed using the Turkish version of the Menopause Rating Scale, for which validity and reliability have been established. The scale consists of 11 items and the total score ranges from 0 to 44. Higher scores indicate greater severity of menopausal symptoms.

Assessment of Sleep Quality

Sleep quality will be assessed using the Turkish version of the Pittsburgh Sleep Quality Index, for which validity and reliability have been established. The total score ranges from 0 to 21, with a score ≤5 indicating good sleep quality.

Assessment of Diet Satisfaction

Diet satisfaction will be assessed at the end of the intervention using the Diet Satisfaction Scale. The Turkish version of the scale has established validity and reliability. The scale consists of 9 items and uses Likert-type scoring. The maximum possible score is 45, with higher scores indicating greater diet satisfaction.

Blood Pressure Measurement

Blood pressure will be measured by the study nurse. Systolic and diastolic blood pressure (mmHg) and heart rate (beats/minute) will be measured using an automatic oscillometric blood pressure monitor (OMRON M2 Basic), with the participant seated and the measurement taken once from the right arm.

Before measurement, participants will be asked about recent exercise, food intake, medication use, and tea or coffee consumption. Participants will rest for at least 5 minutes before blood pressure measurement.

Biochemical Assessments

Venous blood samples will be collected from all participants at baseline (week 0) and at the end of the intervention (week 12), following at least 10 hours of fasting. Blood samples will be collected by the study nurse in the morning, and all biochemical analyses will be performed in the laboratory of Cihanbeyli State Hospital.

The following parameters will be analyzed: fasting blood glucose (mg/dL), fasting insulin (mIU/L), HbA1c (%), total cholesterol (mg/dL), HDL cholesterol (mg/dL), LDL cholesterol (mg/dL), triglycerides (mg/dL), alanine aminotransferase (ALT; U/L), aspartate aminotransferase (AST; U/L), ferritin (ng/mL), 25-hydroxyvitamin D (ng/mL), vitamin B12 (ng/L), C-reactive protein (CRP; mg/L), neutrophil-to-lymphocyte ratio, and thyroid-stimulating hormone (TSH; mIU/L).