Insulin sensitivity affects propensity to obesity in an ethnic-specific manner: results from two controlled weight loss intervention studies

Barbara A Gower,Gary R Hunter,Jessica A Alvarez,Nikki C Bush

doi:10.1186/1743-7075-10-3

Abstract

BackgroundRisk for obesity differs with ethnicity/race and is associated with insulin sensitivity (SI), insulin responsiveness, and dietary glycemic load (GL). The objective of this study was to test the hypotheses that, 1) obesity-prone, normal weight, African-American (AA) women would be more insulin sensitive than BMI-matched, never overweight AA women; 2) increased adiposity over time would be associated with greater baseline SI and higher dietary GL in AA but not European-American (EA) women; and 3) increased adiposity over time would be predicted by SI in women with high but not low acute insulin response to glucose (AIRg).MethodsTwo controlled weight loss interventions were conducted involving overweight (BMI 25.0-29.9 kg/m2) premenopausal AA and EA women. The first included matching with normal-weight (BMI <25.0 kg/m2) controls following weight loss, and then comparing SI. The second included a 1-year follow-up of weight-reduced participants to identify predictors of change in %body fat. Main outcome measure in the first study was insulin sensitivity (SI) as assessed with intravenous glucose tolerance test (IVGTT), and in the second study was change in %fat, as assessed with DXA, over one year. AIRg was assessed during IVGTT, and free-living diet was determined by food record.ResultsIn the first study, formerly overweight AA women were 43% more insulin sensitive than BMI-matched never overweight AA (P < 0.05). In the second study, SI was positively associated with change in %fat over 1 year only in AA women (P < 0.05) and women with high AIRg (P < 0.05). In addition, AA who were insulin sensitive and who consumed a higher GL diet tended to gain greater %fat (P = 0.086 for diet x SI interaction). In both studies, AA women had higher AIRg (P < 0.001) than EA women.ConclusionsFormerly overweight (obesity-prone) AA women were more insulin sensitive than never overweight AA women, a quality that may predispose to adiposity, particularly when combined with a high GL diet. This ethnicity/race-specific effect may be due to high insulin responsiveness among AA.

Highlights

Risk for obesity differs with ethnicity/race and is associated with insulin sensitivity (SI), insulin responsiveness, and dietary glycemic load (GL)
The objective of the study was to test the hypotheses that, 1) obesity-prone, normal weight, African-American (AA) women would be more insulin sensitive than BMImatched, never overweight AA women; 2) increased adiposity over time would be associated with greater baseline sensitivity index (SI) and higher dietary GL in AA but not EuropeanAmerican (EA) women; and 3) increased adiposity over time would be predicted by SI in women with high but not low acute insulin response to glucose (AIRg)
We reported that in the combined group of women, greater insulin sensitivity predicted greater gain in %body fat over 1 year; that greater glucose disposal predicted less gain in intra-abdominal fat; and that dietary glycemic load interacted with insulin sensitivity to predict gain in adiposity [17]

Summary

Introduction

Risk for obesity differs with ethnicity/race and is associated with insulin sensitivity (SI), insulin responsiveness, and dietary glycemic load (GL). The objective of this study was to test the hypotheses that, 1) obesity-prone, normal weight, African-American (AA) women would be more insulin sensitive than BMI-matched, never overweight AA women; 2) increased adiposity over time would be associated with greater baseline SI and higher dietary GL in AA but not European-American (EA) women; and 3) increased adiposity over time would be predicted by SI in women with high but not low acute insulin response to glucose (AIRg). U.S epidemiological data indicate that the age-adjusted rate of overweight and obesity is 82% in AA women, and the prevalence of grade 3 obesity is higher in AA women (18%) than in all other race/gender sub-groups [1] The reason for this disparity is not clear, There are several ways through which insulin may promote adiposity. The effect of insulin on voluntary food intake in humans is complex, and neither its actions nor their mechanisms have been entirely elucidated [11]

Objectives

Methods

Results

Discussion

Conclusion