This randomized, crossover interventional study evaluates the effects of real-time (open) versus blinded continuous glucose monitoring (CGM) on glycemic variability, lifestyle behaviors, and metabolic outcomes in adults with prediabetes and overweight or obesity (BMI ≥ 27 kg/m²). Thirty participants will undergo both open and blinded CGM phases, separated by a washout period. The study aims to assess whether access to real-time glucose data promotes behavioral change and improves metabolic health compared with blinded CGM use.

Prediabetes and obesity are major contributors to the development of type 2 diabetes and its complications. Early intervention focused on glycemic control and lifestyle modification is essential to prevent disease progression. Continuous glucose monitoring (CGM) provides real-time insight into glucose dynamics and may support behavioral change; however, evidence is limited on how access to glucose data influences sustained lifestyle modification and metabolic outcomes in individuals with prediabetes.

The primary objectives are to assess the impact of real-time (open) versus blinded CGM on (1) glycemic variability using sensitive dynamic metrics, and (2) behavioral changes, including dietary habits and physical activity, in adults with prediabetes and overweight or obesity.

Secondary objectives include evaluating the effects of CGM on anthropometric and metabolic parameters, biochemical and physiological markers of metabolic control, participant experience and acceptability of CGM, sustainability of lifestyle changes, and associations between glycemic variability and cardiometabolic risk reduction.

This prospective, randomized, open-label, blinded crossover interventional study will evaluate the effects of CGM on behavior, glycemic variability, and weight loss in adults with prediabetes and obesity (BMI ≥ 27 kg/m²). Thirty participants will be recruited from the Diabetes Outpatient Clinic of the Community Health Center Koper. After screening and a 10-day blinded CGM run-in period, participants will be randomized (1:1) to one of two sequences: (A) open CGM for 12 weeks followed by a 30-day washout and 12 weeks of blinded CGM, or (B) blinded CGM for 12 weeks followed by washout and 12 weeks of open CGM. Participants will attend baseline and follow-up visits for anthropometric, biochemical, and behavioral assessments during each study phase.

Inclusion Criteria:

• Adults aged 18-70 years.
• BMI ≥ 27 kg/m² (overweight or obese).
• Prediabetes, confirmed by:

Impaired fasting glucose (IFG: 5.6-6.9 mmol/L), and/or Impaired glucose tolerance (IGT: 2-hour OGTT glucose 7.8-11.0 mmol/L).

• Stable body weight (±3 kg) in the last 3 months.
• No current use of antidiabetic or weight-loss medications.
• Willingness and ability to wear a CGM device as instructed.
• Capacity to provide written informed consent.
• Recruitment from the Diabetes Outpatient Clinic, Community Health Center Koper (identified and invited from the clinic's database).

Exclusion Criteria:

• Diagnosis of type 1 or type 2 diabetes mellitus (fasting glucose ≥ 7.0 mmol/L or HbA1c ≥ 6.5%).
• Current or recent (within 3 months) use of:
• Any antidiabetic medication (insulin, metformin, GLP-1RA, SGLT2i, etc.), or anti-obesity pharmacotherapy.
• Pregnancy, breastfeeding, or planned pregnancy during the study period.
• Severe chronic disease that could influence glucose metabolism or study participation (e.g., chronic liver disease, renal failure, active malignancy).
• Endocrine disorders affecting metabolism (e.g., untreated thyroid disease, Cushing's syndrome).
• Severe psychiatric illness or cognitive impairment limiting adherence or comprehension.
• Use of medications known to affect glucose metabolism (e.g., corticosteroids, atypical antipsychotics).
• Implanted electronic medical devices (e.g., pacemaker, defibrillator) that may interfere with CGM function.
• Known allergy or skin reaction to CGM adhesives or device materials.
• Participation in another interventional study within the previous 3 months.