Interethnic Differences in Muscle, Liver and Abdominal Fat Partitioning in Obese Adolescents

Abstract

The prevalence of insulin resistance and type 2 diabetes (T2D) in obese youth is rapidly increasing, especially in Hispanics and African Americans compared to Caucasians. Insulin resistance is known to be associated with increases in intramyocellular (IMCL) and hepatic fat content. We determined if there are ethnic differences in IMCL and hepatic fat content in a multiethnic cohort of 55 obese adolescents. We used 1H magnetic resonance spectroscopy (MRS) to quantify IMCL levels in the soleus muscle, oral glucose tolerance testing to estimate insulin sensitivity, magnetic resonance imaging (MRI) to measure abdominal fat distribution. Liver fat content was measured by fast–MRI. Despite similar age and % total body fat among the groups, IMCL was significantly higher in the Hispanics (1.71% [1.43%, 2.0%]) than in the African-Americans (1.04% [0.75%, 1.34%], p = 0.013) and the Caucasians (1.2% [0.94%, 1.5%], p = 0.04). Liver fat content was undetectable in the African Americans whereas it was two fold higher than normal in both Caucasians and Hispanics. Visceral fat was significantly lower in African Americans (41.5 cm2 [34.6, 49.6]) and was similar in Caucasians (65.2 cm2 [55.9, 76.0]) and Hispanics (70.5 cm2 [59.9, 83.1]). In a multiple regression analysis, we found that ethnicity independent of age, gender and % body fat accounts for 10% of the difference in IMCL. Our study indicates that obese Hispanic adolescents have a greater IMCL lipid content than both Caucasians and African Americans, of comparable weight, age and gender. Excessive accumulation of fat in the liver was found in both Caucasian and Hispanic groups as opposed to virtually undetectable levels in the African Americans. Thus, irrespective of obesity, there seem to be some clear ethnic differences in the amount of lipid accumulated in skeletal muscle, liver and abdominal cavity.

Ethnic Differences in the Link Between Insulin Resistance and Elevated ALT

“…18,46 Non-Hispanic blacks also have a low prevalence of MetS diagnosis, predominantly related to having lower triglyceride levels than other racial/ethnic groups, 47 making MetS a poorer marker of IR in nonHispanic blacks. 26,32,35,48 Our present findings build on these assertions by revealing that even in the presence of elevated WC and HOMA-IR, non-Hispanic black adolescents have a lower OR than non-Hispanic whites for suspected NAFLD.…”

“…Although the cross-sectional nature of these data limits the conclusions we can make regarding these relationships, these findings overall suggest a lower degree of association among MetS, IR, and NAFLD in nonHispanic black adolescents compared with non-Hispanic whites and Hispanics, as illustrated by Table 3 and Fig 1A. These findings may pertain to differences in body fat distribution among non-Hispanic blacks, who notably have less visceral adiposity. 31,46 Although visceral obesity is tightly linked to IR, this link does not appear necessary in non-Hispanic blacks. 53 However, nonHispanic blacks have more subcutaneous fat.…”

“…31,46 Although visceral obesity is tightly linked to IR, this link does not appear necessary in non-Hispanic blacks. 53 However, nonHispanic blacks have more subcutaneous fat.…”

“…53 However, nonHispanic blacks have more subcutaneous fat. 46 Basic science studies have suggested that the ability to deposit large quantities of fat in subcutaneous tissue protects against deposition in visceral and hepatic compartments. 18,54 Nevertheless, we noted that even when WC is elevated in non-Hispanic black adolescents, suggesting increase in visceral adipose tissue, there were lower ORs for suspected NAFLD than seen for non-Hispanic whites (Fig 1B).…”

Body composition phenotypes in pathways to obesity and the metabolic syndrome

“…91 (iv) There is also emerging evidence that African Americans have less hepatic and intramyocellular lipid levels than Caucasians or Hispanic Americans. [91][92][93] Furthermore, intramyocellular lipid has been reported to be a significant determinant of insulin sensitivity among healthy, young European Americans, but not among African-American women. 94 At high levels of adiposity, however, African-American men, though not women, have greater quantities of total body intermuscular fat (IMAT) than do Asians or Whites after adjustment for differences in total adiposity and other covariates.…”