Similar Blood Glucose Pattern with Highest Peak at Minute 45 on Oral Glucose Tolerance Test Despite Higher Fasting Insulin and Insulin Resistance in Healthy Obese than Non-Obese Subject.
Level 4 - case-series / case-control
Cross-sectional comparative study with age- and sex-matched controls
What was done
This study evaluated 32 age- and sex-matched participants divided into two equal groups (16 obese and 16 non-obese) at Sanglah Hospital, Denpasar. Obesity was defined as BMI ≥25 kg/m² and waist circumference ≥80 cm for females or ≥90 cm for males; non-obesity was defined as BMI 18–25 kg/m² and waist circumference <80 cm for females or <90 cm for males. Fasting insulin and blood glucose were measured at minutes 0, 15, 30, 45, 60, 75, 90, and 120 after a 75-gram oral glucose load. Insulin resistance was calculated via HOMA-IR, and participants were classified with normal glucose tolerance (NGT) or impaired glucose tolerance (IGT) based on ADA criteria.
What was found
Fasting insulin was significantly higher in obese than non-obese subjects (median 12.75 [range 3.70–41.30] vs 3.80 [1.80–36.80] µU/mL, p=0.041), as was HOMA-IR (median 2.45 [0.70–8.00] vs 0.80 [0.40–8.50], p=0.001). Fasting insulin correlated with BMI (r=0.559, p=0.001) and waist circumference (r=0.633, p<0.001). HOMA-IR also correlated with BMI (r=0.528, p=0.002) and waist circumference (r=0.600, p<0.001). Across all subgroups (obese IGT, obese NGT, non-obese IGT, non-obese NGT), blood glucose curves showed two distinct peaks: the highest peak at minute 45 in all groups, and a lower second peak at minute 75 in NGT and minute 90 in IGT subjects. Blood glucose was consistently higher at every time point in obese compared to non-obese participants.
Why it matters
This study shows that although obesity and insulin resistance elevate overall post-load blood glucose levels, the timing of the primary glucose peak during an OGTT (minute 45) remains unchanged compared to non-obese controls.
Limits
The sample size was very small (16 subjects per group), limiting statistical power for subgroup analyses between NGT and IGT participants. The study was conducted at a single hospital center. Post-load insulin dynamics and C-peptide were not measured during the OGTT, and the cross-sectional design cannot establish longitudinal progression to diabetes.
Cited by
- supports In a standard oral glucose tolerance test, blood glucose levels peak in approximately 40 to 60 minutes.