Ethnic differences in lipoprotein subclasses in obese adolescents: importance of liver and intraabdominal fat accretion

Abstract

Background: Recently, the deleterious metabolic effects of visceral fat [visceral adipose tissue (VAT)] deposition were challenged, and liver fat emerged as having a key independent role in the modulation of cardiometabolic risk factors.

Objective: We explored the relation between liver fat content and VAT in 3 ethnic groups and evaluated whether the ethnic differences in the distributions of lipoprotein concentrations and sizes were associated with the hepatic fat fraction (HFF), VAT, or both.

Design: In a multiethnic group of 33 white, 33 African American, and 33 Hispanic obese adolescents with normal glucose tolerance, we measured VAT and HFF by using magnetic resonance imaging. Fasting lipoprotein particle number and size were measured by using nuclear magnetic resonance spectroscopy. To assess the association between VAT and HFF, we categorized VAT into tertiles.

Results: In each ethnic group, HFF values increased between successive tertiles of VAT. After multivariate adjustment and in comparison with the 2 other groups, African Americans showed lower triglyceride (P = 0.001) and higher HDL (P = 0.03) concentrations, lower concentrations of total (P = 0.007), large (P = 0.005), and medium (P lt 0.0001) VLDL, but higher concentrations of large HDL particles (P = 0.01) and larger HDL (P = 0.005). In multivariate linear models, independent of ethnicity, VAT was a significant predictor for large HDL (P = 0.003) and total small LDL (P = 0.001) concentrations, whereas HFF significantly predicted large VLDL (P = 0.03) concentrations.

Conclusion: Liver fat accretion, independent of VAT, may play a role in the ethnic differences seen in large VLDL particles. This trial was registered at clinicaltrials.gov as NCT00536250.

FIGURE 1.

Hepatic fat fraction (HFF) across visceral fat tertiles in obese adolescents of different ethnicity. Data are presented as box plots of HFF by tertiles of visceral adipose tissue (VAT) within each race (smallest observation, lower quartile, median, upper quartile, and largest observation). For each ethnicity, the nonparametric Kruskal-Wallis test was used to compare the distribution of HFF across tertiles of VAT (whites: P = 0.002; Hispanics: P = 0.004; African Americans: P = 0.1). Wilcoxon's rank sum test was used to conduct post hoc pairwise comparisons between tertiles. Critical α < 0.02 (Bonferroni correction).

FIGURE 2.

Hypothetical origin of the cardiometabolic risk profile by ethnicity in obese adolescents.