Insulin resistance and body fat distribution in South Asian men compared to Caucasian men

Abstract

Objective: South 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 methods: Twenty-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.

Results: Compared 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 microm2; 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.

Conclusions: Insulin 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.

Figure 1. Relationship between Total and regional body fat distribution and body mass index (A–D).

Relationship between total body fat and (E) waist circumference and (F) truncal skinfolds. Spearman correlation coefficients and p-values for South Asians and Caucasians respectively are as follows: A: r = 0.71, p<0.0001 and r = 0.69, p = 0.001; B: r = 0.74, p<0.0001 and r = 0.70, p = 0.002; C: r = 0.81, p<0.0001 and r = 0.74, p = 0.0004; D: r = 0.78, p<0.0001 and r = 0.62, p = 0.006; E: r = 0.83, p<0.0001 and r = 0.66, p = 0.003; F: r = 0.82, p<0.0001 and r = 0.86, p<0.0001. South Asians are depicted as dark triangles, solid line and Caucasians are depicted as white squares and dotted line.

Figure 2. Relationship between glucose disposal rate and total and regional body fat (A–C).

Spearman correlation coefficients and p-values for South Asians and Caucasians respectively are as follows: A: r = −0.42, p = 0.02 and r = −0.58, p = 0.01; B: r = −0.40, p = 0.03 and r = −0.39, p = 0.05; C: r = −0.04, p = 0.03 and r = −0.39, p = 0.04. South Asians: dark triangles, solid line and Caucasians: white squares and dotted line

Figure 3. Representative pictures of the enlarged adipocytes from South Asian (left panel) and Caucasian (right panel) volunteers.

Both images were obtained with SPOT digital camera using 10× magnification.

Figure 4. Adipocyte size in the abdominal subcutaneous area is correlated to A) glucose disposal rate during hyperinsulinemic-euglycemic clamp and to B) plasma adiponectin concentrations.

Spearman correlation coefficients and p-values for South Asians and Caucasians respectively are as follows: A: r = −0.57, p = 0.0008; B: r = −0.71, p = <0.0001. South Asians: dark triangles, solid line and Caucasians: white squares and dotted line

Figure 5. Body composition, abdominal subcutaneous adipocyte size, plasma adiponectin and glucose disposal rate in South Asian (dark bar) and Caucasian (open bar) men who had total body fat <25% and underwent fat biopsy from subcutaneous abdominal area.

Mann-Witney U test was used to compare groups. Log transformation was done for skewed values (Rd, Adiponectin and Leptin) for calculation of p value.