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Comparative Study
. 2005 Dec;82(6):1210-7.
doi: 10.1093/ajcn/82.6.1210.

Independent association of insulin resistance with larger amounts of intermuscular adipose tissue and a greater acute insulin response to glucose in African American than in white nondiabetic women

Jeanine B Albu  1 , Albert J Kovera, Lynn Allen, Marsha Wainwright, Evan Berk, Nazia Raja-Khan, Isaiah Janumala, Bryan Burkey, Stanley Heshka, Dympna Gallagher
Affiliations
Comparative Study

Independent association of insulin resistance with larger amounts of intermuscular adipose tissue and a greater acute insulin response to glucose in African American than in white nondiabetic women

Jeanine B Albu et al. Am J Clin Nutr. 2005 Dec.

Abstract

Background: African Americans (AAs) have a higher prevalence of obesity and type 2 diabetes than do whites. Higher insulin resistance and hyperinsulinemia have been reported in adult AAs than in whites. Differences in adipose tissue and its distribution may account for these findings.

Objective: The objective was to ascertain whether differences between AA and white women in adipose tissue (AT) and skeletal muscle (SM) volumes account for ethnic differences in insulin resistance.

Design: We used whole-body magnetic resonance imaging to measure AT and SM volumes and used the intravenous-glucose-tolerance test to measure insulin resistance.

Results: AAs (n = 32) were 29-42% more insulin resistant than were whites (n = 28) after adjustment for weight and height or any AT volumes (P < 0.05). After adjustment for SM volume, the difference decreased to 19% and became nonsignificant. AAs had a 163% greater acute insulin response to glucose than did whites; this difference was significant even after adjustment for insulin sensivitity index, weight, height, and any magnetic resonance imaging measures. With respect to regional AT volumes, an association independent of race, weight, height, and SM volume was found only between increased intermuscular AT and lower insulin sensitivity index.

Conclusions: Premenopausal AA women had significantly higher insulin resistance and acute insulin response to glucose than did their white counterparts. Whereas the difference in insulin resistance was partially accounted for by a greater SM volume in the AAs than in the whites, the difference in the acute insulin response to glucose was independent of any AT and SM measures and was disproportionately larger than expected according to the difference in insulin resistance. In addition, whole-body intermuscular AT was an important independent correlate of insulin resistance.

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Conflict of interest statement

JBA was responsible for the design of the study; JBA, AJK, LA, MW, EB, NR-K, and BB were responsible for subject recruitment and data collection; DG and IJ were responsible for magnetic resonance imaging analyses; JBA, AJK, and SH were responsible for data analysis; SH provided statistical expertise; JBA was responsible for data interpretation and manuscript writing; and JBA, AJK, LA, MW, EB, BB, SH, and DG were responsible for critical review of the manuscript for intellectual content. BB is an employee of Novartis Pharma Corporation; JBA has received research support from Novartis Pharma Corporation to study insulin resistance and its relation with body composition before and after weight loss. None of the other authors had any personal or financial conflicts of interest.

Figures

FIGURE 1
FIGURE 1
Relation between body weight and skeletal muscle volume, measured with whole-body magnetic resonance imaging (MRI), in African American (●, straight line) and white (○, dashed line) women. Skeletal muscle was measured by whole-body MRI. The slopes of the regression lines were significantly different (P < 0.05, general linear model).
FIGURE 2
FIGURE 2
Relation between total visceral adipose tissue (VAT) volume, measured with whole-body magnetic resonance imaging, and the insulin sensitivity index (SI), calculated by using the minimal model, from data obtained during the intravenous-glucose-tolerance test in African American (●, straight line) and white (○, dashed line) women. The slopes of the regression lines were not significantly different (P = 0.42). SI was significantly lower in the African American than in the white women (P < 0.001, analysis of covariance) after adjustment for VAT. A general linear model was used to test homogeneity of slopes.
FIGURE 3
FIGURE 3
Relation between total subcutaneous adipose tissue (SAT) volume, measured with whole-body magnetic resonance imaging, and the insulin sensitivity index (SI), calculated by using the minimal model, from data obtained during the intravenous-glucose-tolerance test in African American (●, straight line) and white (○, dashed line) women. The slopes of the regression lines were not significantly different (P = 0.47). SI was significantly lower in the African American than in the white women (P < 0.001, analysis of covariance) after adjustment for SAT. A general linear model was used to test homogeneity of slopes.
FIGURE 4
FIGURE 4
Relation between total intermuscular adipose tissue (IMAT) volume, measured with whole-body magnetic resonance imaging, and the insulin sensitivity index (SI), calculated by using the minimal model, from data obtained during the intravenous-glucose-tolerance test in African American (●, straight line) and white (○, dashed line) women. The slopes of the regression lines were not significantly different (P = 0.32). SI was significantly lower in the African American than in the white women (P < 0.05, analysis of covarianc) after adjustment for IMAT. A general linear model was used to test homogeneity of slopes.
FIGURE 5
FIGURE 5
Relation between total skeletal muscle (SM) volume, measured with whole-body magnetic resonance imaging, and the insulin sensitivity index (SI), calculated by using the minimal model, from data obtained during the intravenous-glucose-tolerance test in African American (●, straight line) and white (○, dashed line) women. The slopes of the regression line were not significantly different (P = 0.86). SI did not differ significantly between the African American and the white women (P = 0.17, analysis of covariance) after adjustment for SM. A general linear model was used to test homogeneity of slopes.
FIGURE 6
FIGURE 6
Relation between the insulin sensitivity index (SI) and the acute insulin response to intravenous glucose (AIRg) in African American (●, straight line) and white (○, dashed line) women. SI was calculated by using the minimal model, and AIRg was calculated as the mean incremental value over baseline for the first 8 min after the glucose injection, with the use of data obtained during the intravenous-glucose-tolerance test. The slopes of the regression lines did not differ significantly (P = 0.15). AIRg was significantly higher in the African American than in the white women (P < 0.005, analysis of covariance) after adjustment for SI. A general linear model was used to test homogeneity of slopes.
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