Abstract
ObjectiveSouth Asians are susceptible to insulin resistance even without obesity. We examined the characteristics of body fat content, distribution and function in South Asian men and their relationships to insulin resistance compared to Caucasians.Research Design and MethodsTwenty-nine South Asian and 18 Caucasian non-diabetic men (age 27±3 and 27±3 years, respectively) underwent euglycemic-hyperinsulinemic clamp for insulin sensitivity, underwater weighing for total body fat, MRI of entire abdomen for intraperitoneal (IP) and subcutaneous abdominal (SA) fat and biopsy of SA fat for adipocyte size.ResultsCompared to Caucasians, in spite of similar BMI, South Asians had higher total body fat (22±6 and 15±4% of body weight; p-value<0.0001), higher SA fat (3.5±1.9 and 2.2±1.3 kg, respectively; p-value = 0.004), but no differences in IP fat (1.0±0.5 and 1.0±0.7 kg, respectively; p-value = 0.4). SA adipocyte cell size was significantly higher in South Asians (3491±1393 and 1648±864 µm2; p-value = 0.0001) and was inversely correlated with both glucose disposal rate (r-value = −0.57; p-value = 0.0008) and plasma adiponectin concentrations (r-value = −0.71; p-value<0.0001). Adipocyte size differences persisted even when SA was matched between South Asians and Caucasians.ConclusionsInsulin resistance in young South Asian men can be observed even without increase in IP fat mass and is related to large SA adipocytes size. Hence ethnic excess in insulin resistance in South Asians appears to be related more to excess truncal fat and dysfunctional adipose tissue than to excess visceral fat.
Highlights
Type 2 diabetes is common among persons of South Asian origin [1]
The following questions are addressed: (a) do BMI-matched South Asians have more total body fat and abdominal subcutaneous fat than Caucasians? (b) do South Asian men with BMI in the normal range have more visceral fat than Caucasians matched for BMI? (c) can greater insulin resistance in South Asians be explained by preferential accumulation of (i) intraperitoneal fat or (ii) abdominal subcutaneous fat ? (d) does abdominal subcutaneous adipose tissue in South Asians differ in structure or function compared to Caucasians?
We have shown that abnormalities in adipose tissue amounts, distribution, and function can account for a significant portion of the predisposition of South Asians to insulin resistance, we cannot rule out the possibility that genetic factors of a more generalized nature contribute to insulin resistance
Summary
Type 2 diabetes is common among persons of South Asian origin [1]. We reported that a genetic polymorphism in PC-1 is relatively frequent in South Asians and is associated with increased insulin resistance and type 2 diabetes [5,6]. The following questions are addressed: (a) do BMI-matched South Asians have more total body fat and abdominal subcutaneous fat than Caucasians? (b) do South Asian men with BMI in the normal range have more visceral fat (intraperitoneal fat) than Caucasians matched for BMI? (c) can greater insulin resistance in South Asians be explained by preferential accumulation of (i) intraperitoneal fat or (ii) abdominal (truncal) subcutaneous fat ? (d) does abdominal subcutaneous adipose tissue in South Asians differ in structure or function compared to Caucasians? The following questions are addressed: (a) do BMI-matched South Asians have more total body fat and abdominal subcutaneous fat than Caucasians? (b) do South Asian men with BMI in the normal range have more visceral fat (intraperitoneal fat) than Caucasians matched for BMI? (c) can greater insulin resistance in South Asians be explained by preferential accumulation of (i) intraperitoneal fat or (ii) abdominal (truncal) subcutaneous fat ? (d) does abdominal subcutaneous adipose tissue in South Asians differ in structure or function compared to Caucasians?
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