A Case for Early Screening of Fasting Insulin

Introduction

Current clinical guidelines for diagnosing metabolic syndrome (MetSy) do not include fasting insulin as a standard screening test. However, emerging research suggests that measuring fasting insulin provides critical insights into metabolic dysfunction that precede traditional markers such as fasting glucose, lipids, and blood pressure. By identifying hyperinsulinemia early, clinicians can tailor lifestyle interventions to optimize patient outcomes and prevent the progression of MetSy.

The Role of Hyperinsulinemia in Metabolic Syndrome

MetSy is characterized by insulin resistance, and hyperinsulinemia often precedes overt metabolic abnormalities by several years. Research suggests that early-phase insulin secretion is increased in individuals with normal fasting glucose but MetSy, indicating beta-cell dysfunction as an early metabolic defect (Spadaro et al., 2011). Additionally, impaired beta-cell function and increased insulin resistance can be detected well before the development of impaired fasting glucose or impaired glucose tolerance (Cubeddu & Hoffmann, 2012). These findings underscore the importance of fasting insulin as an early biomarker for metabolic dysfunction.

Evidence Supporting Early Screening

A growing body of literature supports expanding MetSy screening criteria to include fasting insulin. A study on obese adolescents found that insulin resistance was present in 56.7% of participants, while only 14.4% met the MetSy criteria, suggesting that traditional markers fail to capture early metabolic dysfunction (Davidsson et al., 2020). Similarly, research on the Japanese population found that insulin levels were more predictive of MetSy than glycated hemoglobin (HbA1c) or fasting glucose, highlighting insulin’s utility as an early screening tool (Saravia et al., 2015).

Clinical Implications of Fasting Insulin Measurement

1. Exercise Prescription
   

   • Patients with significantly elevated fasting insulin often struggle with effective recovery due to the anabolic and anti-lipolytic effects of insulin, which impair mitochondrial function (Spadaro et al., 2011).

   • In these cases, dietary strategies (e.g., carbohydrate reduction, intermittent fasting) should be prioritized before introducing high-intensity exercise.

   • As insulin levels improve, exercise tolerance increases, enabling structured strength and endurance training.

   
   

2. Patient Expectations & Compliance
   

   • Many patients with insulin resistance struggle with traditional weight loss methods because persistently high insulin levels inhibit fat oxidation (Saravia et al., 2015).

   • Measuring fasting insulin educates patients about the physiological barriers to weight loss, reducing frustration and improving adherence to targeted interventions.

   • Understanding their condition as a hormonal imbalance rather than a failure of willpower enhances compliance and long-term success.

   
   

3. Metabolic Flexibility & Treatment Prioritization
   

   • Severe hyperinsulinemia impairs metabolic flexibility, making carbohydrate metabolism dysfunctional (Cubeddu & Hoffmann, 2012).

   • A phased approach starting with low-insulin-stimulating diets, followed by strategic exercise integration, leads to better long-term outcomes than immediate high-intensity training.

   • This approach prevents overtraining and discouragement in patients who are metabolically inflexible.

The Case for Routine Fasting Insulin Screening

Despite growing evidence supporting its predictive value, fasting insulin remains underutilized in clinical practice. The current reliance on fasting glucose and HbA1c fails to detect the earliest stages of metabolic dysfunction. Studies have shown that MetSy and insulin resistance can exist in individuals with normal glucose tolerance, reinforcing the need for broader screening (Kumar et al., 2019).

Expanding screening criteria to include fasting insulin would:

1. Identify high-risk individuals earlier, allowing for more effective intervention.

2. Improve patient education and adherence to lifestyle changes.

3. Enable a more individualized approach to metabolic health management.

Conclusion

Early screening of fasting insulin provides valuable insights into metabolic dysfunction that precede traditional markers of MetSy. By incorporating fasting insulin into routine screening, clinicians can better tailor interventions, improve patient compliance, and prevent the progression of metabolic diseases. Given its strong association with MetSy and its predictive power for future metabolic deterioration, fasting insulin should be a standard component of metabolic health assessment.

References

• Spadaro, A., & Alagona, C. (2011). Early-phase insulin secretion is increased in subjects with metabolic syndrome. Retrieved from Consensus.

• Cubeddu, L., & Hoffmann, I. (2012). Impact of traits of metabolic syndrome on β-cell function. Retrieved from Consensus.

• Davidsson, L., & Alkhabbaz, M. (2020). Intermediate hyperglycaemia, insulin resistance, and metabolic dysfunction in adolescents. Retrieved from Consensus.

• Saravia, F., & Civeira, F. (2015). Glycated hemoglobin, fasting insulin, and the metabolic syndrome in the Japanese population. Retrieved from Consensus.

• Kumar, S. K. (2019). Risk of insulin resistance in normal glucose-tolerant individuals. Retrieved from Consensus.