Hayashi 2013: Insulin Patterns During OGTT Predict Diabetes Risk

In 2013, Dr. Tomoshige Hayashi and colleagues published a groundbreaking 10-year study following Japanese Americans, revealing that the pattern of insulin response during an oral glucose tolerance test (OGTT) predicts diabetes risk far better than any single measurement.

The Kraft Legacy Extended

This study builds on Dr. Joseph Kraft's pioneering work identifying insulin response patterns. Hayashi's team applied rigorous statistical analysis to quantify what Kraft observed clinically: delayed insulin peaks signal metabolic dysfunction years before glucose becomes abnormal.

Study Design

The researchers followed 400 non-diabetic Japanese Americans for 10-11 years, performing detailed OGTT measurements at baseline. They identified five distinct insulin response patterns based on when insulin peaked (30, 60, or 120 minutes) and how levels changed across timepoints.

The Five Patterns

• •Pattern 1: Early peak at 30 min, rapid decline → Lowest risk (3.2% developed diabetes)
• •Patterns 2-3: Intermediate peaks → Moderate risk
• •Pattern 4: Delayed peak at 120 min, rising throughout → Highest risk (47.8% developed diabetes)
• •Pattern 5: Delayed peak with partial compensation → High risk (37.5% developed diabetes)

Clinical Implications

Individuals with delayed insulin peaks (patterns 4 and 5) had dramatically elevated diabetes risk—odds ratios of 12.55 and 8.34 respectively compared to early responders. These patterns identify beta cell dysfunction and insulin resistance years before fasting glucose or HbA1c become diagnostic.

Why This Matters

A standard 2-hour OGTT with insulin measurements at multiple timepoints can reveal metabolic trajectory that single fasting measurements miss entirely. Early intervention becomes possible when dysfunction is still reversible.