The GLOW UP study is a single-center, prospective, observational case-control study conducted in St. Gallen, Switzerland. The primary aim of the study is to examine to what degree lifestyle data collected from wearable devices and a smartphone app can identify individuals with prediabetes (vs. normoglycemic) in a real-world setting. The study also aims to characterize variability in lifestyle and glycemic patterns and to examine how between- and within-person differences relate to diabetes risk; to identify personalized predictors of early metabolic dysregulation. The study also evaluates new image-based meal tracking algorithms for predicting glycemic control and examines how reminder messages influence adherence to a ~4-week meal logging protocol.

The study aims to enroll 200 adults aged 45 years and older with a BMI of at least 25 kg/m² and no known diagnosis of diabetes, including 100 participants with prediabetes and 100 normoglycemic (metabolically healthy) controls. Participants will be classified at the baseline visit using HbA1c and fasting plasma glucose (FPG) tests, with prediabetes defined as HbA1c 5.7-6.4% and/or FPG 5.6-6.9 mmol/L, and normoglycemia defined as HbA1c <5.7% and FPG <5.6 mmol/L, following clinical standards. During the ~4-week observational period, participants will be asked to wear a smart ring, a wrist-worn smartwatch, and a blinded continuous glucose monitor (CGM). Participants will be asked to log/take-images of their meals via a study app and to complete brief questionnaires (e.g., tracking mood, stress, and contextual meal annotations) via ecological momentary assessments. FPG and HbA1c samples will be collected at baseline to classify participants as prediabetic or normoglycemic, and again at follow-up (~4 weeks), which will serve as the primary outcome to evaluate associations between lifestyle and wearable-derived data and diabetes risk status.

Inclusion Criteria:

• Citizens or residents of Switzerland who are German-speaking (main place of living or employment in Switzerland).
• Age ≥45 years.
• BMI ≥25 kg/m² (overweight or obese).
• Regular access to a smartphone (iOS or Android) with a data plan.
• Able to use smartphone applications.
• Able to walk independently.

Exclusion Criteria:

• History of stroke, heart disease, renal failure, cancer, or diabetes (type 1 or type 2).
• Past vascular bypass surgery or angioplasty.
• Current or planned use of glucose-lowering medications during the upcoming 4 weeks (e.g., GLP-1 receptor agonists, metformin).
• Pregnant or breastfeeding.
• Relevant skin conditions at wearable placement sites (e.g., upper arm).
• BMI <25 kg/m² confirmed at enrollment.
• FPG ≥7.0 mmol/L and/or HbA1c ≥6.5% (newly identified type 2 diabetes); Individuals who meet type-2 diabetes criteria at enrollment, based on Swiss/ADA diagnostic criteria will be informed of blood test results and referred to a GP. These individuals will be deemed ineligible and excluded from the study.

Adults ≥45 years with BMI ≥25 kg/m², German-speaking residents of Switzerland, without known diabetes, recruited from GP practices, community and workplace channels, and general public advertisements.