Higher insulin and glucagon-like peptide-1 (GLP-1) levels in healthy, young South Asians as compared to Caucasians during an oral glucose tolerance test

Abstract Objective Higher insulin levels during an oral glucose test (OGTT) have been shown in South Asians. We aimed to investigate if this increased insulin response causes reactive hypoglycemia later on, and if an increased glucagon-like-peptide-1 (GLP-1) response, which could contribute to the hyperinsulinemia, is present in this ethnic group. Methods A prolonged, 6-h, 75-g OGTT was performed in healthy, young Caucasian (n = 10) and South Asian (n = 8) men. The glucose, insulin and GLP-1 response was measured and indices of insulin sensitivity and beta-cell activity were calculated. Results Age (Caucasians (CAU) 21.5 ± 0.7 years vs South Asians (SA) 21.4 ± 0.7 years (mean ± SEM)) and body mass index (CAU 22.7 ± 0.7 kg/m 2 vs SA 22.1 ± 0.8 kg/m 2 ) were comparable between the two groups. South Asian men were more insulin resistant, as indicated by a comparable glucose but significantly higher insulin response, and a significantly lower Matsuda index (CAU 8.7(8.6) vs SA 3.2(19.2), median(IQR)). South Asians showed a higher GLP-1 response, as reflected by a higher area under the curve for GLP-1 (CAU 851 ± 99.8 mmol/l vs SA 1235 ± 155.0 mmol/L). During the whole 6-h period, no reactive hypoglycemia was observed. Conclusion Healthy, young South Asian men have higher insulin levels during an OGTT as compared to Caucasians. This does not, however, lead to reactive hypoglycemia. The hyperinsulinemia is accompanied by increased levels of GLP-1. Whether this is an adaptive response to facilitate hyperinsulinemia to overcome insulin resistance or reflects a GLP-1 resistant state has yet to be elucidated.