Effects of a Mediterranean Diet With Cycling and Rowing Exercise on Blood Sugar in Women With Prediabetes

Continuous Glucose Monitoring in Prediabetics on a Mediterranean Diet With Sequentially Added Cycling and Rowing Training: Study Protocol for a Prospective Non-Randomized Study

The goal of this clinical trial is to learn how a Mediterranean-style diet, with and without added exercise, affects blood sugar control in women with prediabetes. Prediabetes means blood sugar levels are higher than normal but not yet type 2 diabetes. Healthy eating and regular physical activity can help prevent diabetes.

The investigators aim to answer two main questions:

1. Does adding a supervised program of cycling and rowing exercises to the diet lead to better blood sugar control than the diet alone?
2. Do women who recently returned to normal blood sugar levels respond differently to the exercise program than those who currently have high blood sugar?

Participants will be placed into one of three groups based on current blood sugar levels and medical fitness for exercise:

• Group 1 (Diet only): Will follow a Mediterranean eating plan for 12 weeks.
• Group 2 (Diet + Exercise, Current High Blood Sugar): Will follow the same diet and also do supervised exercise (cycling, then rowing) three times a week for 8 weeks.
• Group 3 (Diet + Exercise, Recent Normal Blood Sugar): Will follow the same diet and exercise program as Group 2. These women had prediabetes in the past year but now have normal blood sugar levels.

All participants will follow the study protocol for 12 weeks, which includes the following key components:

• Dietary Intervention: Adherence to a Mediterranean-style eating plan, which emphasizes high intake of vegetables, fruits, whole grains, legumes, olive oil, and fish.
• Continuous Glucose Monitoring: Wearing a continuous glucose monitoring (CGM) device-a small, minimally invasive sensor placed on the upper arm-during multiple 10-day periods. This device tracks interstitial glucose levels throughout the day and night to assess daily glucose patterns.
• Blood Sampling and Analysis: Providing fasting blood samples for the measurement of glycemic and metabolic health markers. These include fasting plasma glucose, hemoglobin A1c (HbA1c), fasting insulin, and 2-hour oral glucose tolerance test (OGTT) results.
• Anthropometric Assessments: Undergoing standardized measurements of height, body weight, body fat percentage (via bioelectrical impedance), waist circumference, and Body Mass Index (BMI) at scheduled intervals.
• Questionnaires: Completing validated surveys to assess habitual dietary intake, sleep quality and duration, and levels of physical activity.

Investigators will compare changes in blood sugar control and other health measures from the start to the end of the 12-week study among the three groups.

This study aims to investigate the effects of a Mediterranean-style diet combined with cycling and rowing exercises on blood sugar control and daily blood sugar fluctuations in women with prediabetes.

Prediabetes is a condition in which blood sugar levels are higher than normal but not high enough to be diagnosed as type 2 diabetes. Importantly, prediabetes can often be reversed with appropriate lifestyle changes. Healthy eating habits and regular physical activity are the most effective ways to prevent the progression from prediabetes to diabetes. However, commonly used blood sugar tests, such as fasting glucose and hemoglobin A1c (HbA1c), do not always reflect daily ups and downs in blood sugar levels.

For this reason, this study will use continuous glucose monitoring (CGM) in addition to standard blood tests. CGM is a small sensor placed on the upper arm that measures blood sugar levels continuously throughout the day and night. This method shows how long blood sugar stays within a healthy range and how much it fluctuates during daily life. These detailed measurements allow a more accurate evaluation of how diet and exercise affect blood sugar control.

One important feature of this study is that it examines not only the effect of diet but also the effects of two different types of exercise. Participants will first perform cycling exercises, which mainly involve the lower body, and then rowing exercises, which engage both the upper and lower body. This approach allows a comparison of how different exercise types influence blood sugar regulation. In addition, evaluation will be based on metabolic background.Women whose blood sugar levels have recently returned to normal will be compared with women who still have prediabetes to determine whether responses differ to the same lifestyle program.

The study will last 12 weeks and will include three groups based on blood sugar status and medical suitability for exercise. The diet-only group will consist of women with prediabetes who are not able to participate in structured exercise for medical reasons and will follow a Mediterranean diet for 12 weeks. The diet plus exercise group will include women with ongoing prediabetes who are medically able to exercise; these participants will follow the Mediterranean diet and perform supervised exercise three times per week for 8 weeks. The third group will consist of women who were diagnosed with prediabetes within the last year but whose blood sugar levels are normal at the start of the study. This group will follow the same diet and exercise program as the second group.

The Mediterranean diet used in this study emphasizes vegetables, fruits, whole grains, legumes, olive oil, and fish, while limiting processed foods and red meat. All participants will receive individual nutrition counseling from a dietitian, and dietary adherence will be monitored regularly.

Exercise programs will be personalized for each participant. Exercise intensity will be determined using a standard exercise test performed at the beginning of the study to measure maximum heart rate. During all exercise sessions, heart rate will be continuously monitored using a chest strap to ensure safe and effective training. All exercise sessions will be conducted under professional supervision at the Faculty of Sport Sciences at Marmara University.

Throughout the study, participants' health status will be evaluated using multiple methods. The main goal is to determine how many participants achieve normal blood sugar levels by the end of the 12-week period. Blood tests will include fasting glucose, an oral glucose tolerance test (OGTT), and HbA1c. In addition, participants will wear a Dexcom G7 continuous glucose monitor during four separate 10-day periods while continuing usual daily activities.

Body weight, waist circumference, and body fat percentage will be measured at regular intervals. Sleep quality and adherence to the Mediterranean diet will be assessed using validated questionnaires.

The collected data will be analyzed to compare changes in blood sugar patterns between the different groups. Because grouping is based on existing health status rather than random assignment, the results will focus on identifying meaningful trends and individual responses rather than establishing strict cause-and-effect relationships.

At the end of this study, it is expected that clearer information will be obtained on how a Mediterranean diet combined with different types of exercise affects blood sugar control in women with prediabetes. The findings may help improve personalized lifestyle strategies for preventing diabetes and maintaining healthy blood sugar levels.

Inclusion Criteria:

• Having a diagnosis of prediabetes (within the last 1 year)

  • Impaired Fasting Glucose (IFG) 100-125 mg/dl
  • OGTT result 2-hour postprandial Impaired Glucose Tolerance (IGT) 140-199 mg/dl
  • HbA1c 5.7-6.4%

• Being between 22-55 years of age

• Being female

• Body Mass Index 18-34.9 kg/m2

• Meeting the criteria in the American College of Sports Medicine (ACSM) and American Heart Association (AHA) cardiovascular disease risk assessment scoring system

• Not engaging in regular planned exercise or physical activity (sedentary)

Exclusion Criteria:

• Diabetes
• Being pregnant
• No self-reported low iron concentrations or anaemia
• Use of medication, insulin, or weight loss injections known to affect lipid and glucose metabolism
• Presence of cardiovascular disease
• Current smoking or excessive alcohol consumption
• Presence of abnormal electrocardiogram (ECG)
• Presence of autonomic neuropathy
• Presence of uncontrolled hypertension (systolic blood pressure >135 mmHg, diastolic blood pressure >85 mmHg)
• Joint-muscle-bone injury limiting exercise