Defining the Human Insulin Resistance Molecular Network; SIGNATURE

This intervention study aims to uncover the molecular mechanisms that underlie insulin resistance in otherwise healthy adults and to explore how short-term lifestyle changes may influence these mechanisms. Insulin resistance is a key feature in the development of type 2 diabetes and other metabolic diseases, but it does not arise uniformly across individuals. The overarching hypothesis is that insulin resistance has multiple underlying causes that differ between individuals, depending on genetic variation and modifiable lifestyle factors such as physical activity and diet.

A total of 80 healthy participants-40 males and 40 females aged between 25 and 55 years-will be recruited. All participants must have a body mass index (BMI) between 18 and 30 and meet strict inclusion and exclusion criteria to minimize confounding variables. Participants will be free of chronic disease, non-smokers, have limited alcohol intake, and not engage in high levels of physical activity. This controlled approach ensures a more accurate assessment of the variables under investigation.

At baseline, all participants will undergo comprehensive phenotyping, including assessments of habitual physical activity, dietary intake, glucose tolerance, and whole-body insulin sensitivity. This will allow the researchers to categorize sub-phenotypes of insulin resistance at both the physiological and molecular level.

Following baseline testing, 40 of the 80 participants will undergo one of two short-term interventions designed to stress metabolic pathways associated with insulin sensitivity:

• Reduced physical activity: Participants will significantly decrease their daily physical activity for 14 days.
• High-fat diet: Participants will consume a hypercaloric high-fat diet for 3 consecutive days.

The aim of these interventions is to test how short-term negative lifestyle changes impact insulin action and related molecular markers, and whether these responses vary between individuals with different phenotypic and genetic profiles.

After the intervention period, selected metabolic tests will be repeated to assess changes in insulin sensitivity and molecular signaling. The primary outcome measure is whole-body insulin action, assessed using gold-standard physiological methods. Exploratory outcomes include identifying cellular and molecular mechanisms contributing to insulin resistance, and understanding the interaction between gene expression and lifestyle responses.

By combining deep phenotyping with short-term interventions, this study will generate new insights into the biological diversity of insulin resistance. Ultimately, this may contribute to the development of more individualized strategies for the prevention and treatment of metabolic diseases.

Inclusion criteria

• Age: 25-55 years
• Body Mass Index (BMI): 18-30 kg/m²
• Healthy (no diagnosed chronic diseases)
• Able and willing to comply with study procedures

Exclusion criteria

• Smoking or nicotine use, current or within the past 5 years
• Alcohol intake exceeding 10 units per week
• Hemoglobin A1c (HbA1c) > 48 mmol/mol (indicative of diabetes or prediabetes)
• Chronic diseases (e.g., cardiovascular disease, diabetes, etc.)
• Chronic medication use, including hormonal treatments
• High physical activity levels (more than 3 hours per week of moderate to vigorous exercise)
• Pregnancy or within 3 months postpartum
• Breastfeeding or within 3 months of cessation
• Abnormal routine blood markers (as defined in lab screening)
• Blood donation within the past 2 months