Body Fat Partitioning Does Not Explain the Interethnic Variation in Insulin Sensitivity Among Asian Ethnicity: The Singapore Adults Metabolism Study

  1. E. Shyong Tai1,2,7
  1. 1Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  2. 2Duke-National University of Singapore Graduate Medical School, Singapore
  3. 3Department of Endocrinology, Tan Tock Seng Hospital, Singapore
  4. 4Singapore Institute for Clinical Sciences, ASTAR, Brenner Centre for Molecular Medicine, Singapore
  5. 5Department of Obstetrics & Gynaecology, National University of Singapore, Singapore
  6. 6Max Planck Institute for Heart and Lung Research, Germany
  7. 7Department of Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  8. 8Singapore Bioimaging Consortium, ASTAR, Singapore
  9. 9Clinical Imaging Research Centre, ASTAR-National University of Singapore, Singapore
  10. 10School of Biological Sciences, Nanyang Technological University, Singapore
  11. 11Department of Pediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  1. Corresponding author: E. Shyong Tai, e_shyong_tai{at}nuhs.edu.sg.

Abstract

We previously showed that ethnicity modifies the association between adiposity and insulin resistance. We sought to determine whether differential body fat partitioning or abnormalities in muscle insulin signaling associated with higher levels of adiposity might underlie this observation. We measured the insulin sensitivity index (ISI), percentage of body fat (%body fat), visceral (VAT) and subcutaneous (SAT) adipose tissue, liver fat, and intramyocellular lipids (IMCL) in 101 Chinese, 82 Malays, and 81 South Asians, as well as phosphorylated (p)-Akt levels in cultured myoblasts from Chinese and South Asians. Lean Chinese and Malays had higher ISI than South Asians. Although the ISI was lower in all ethnic groups when %body fat was higher, this association was stronger in Chinese and Malays, such that no ethnic differences were observed in overweight individuals. These ethnic differences were observed even when %body fat was replaced with fat in other depots. Myoblasts obtained from lean South Asians had lower p-Akt levels than those from lean Chinese. Higher adiposity was associated with lower p-Akt levels in Chinese but not in South Asians, and no ethnic differences were observed in overweight individuals. With higher %body fat, Chinese exhibited smaller increases in deep SAT and IMCL compared with Malays and South Asians, which did not explain the ethnic differences observed. Our study suggests that body fat partitioning does not explain interethnic differences in insulin sensitivity among Asian ethnic groups. Although higher adiposity had greater effect on skeletal muscle insulin sensitivity among Chinese, obesity-independent pathways may be more relevant in South Asians.

Footnotes

  • Received September 29, 2013.
  • Accepted December 10, 2013.

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