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.
Highlights
In African-American and Hispanic youth, T2DM is more common than in individuals of Caucasian origin [1]
Our study compared IMCL level, determined by 1H-magnetic resonance spectroscopy (MRS) and liver fat determined by fast-magnetic resonance imaging (MRI), across ethnicity in a pediatric population of obese adolescents with normal glucose tolerance
Our study showed that African-Americans had lower IMCL and liver fat content than Hispanics
Summary
In African-American and Hispanic youth, T2DM is more common than in individuals of Caucasian origin [1]. The ethnicity-related higher prevalence of T2DM is attributed to a greater degree of obesity and severity of insulin resistance[2]. Several studies have demonstrated decreased insulin sensitivity and hyperinsulinemia in healthy African-American and Hispanic children compared with their Caucasian peers [3,4,5]. The reasons for these ethnic differences have not yet been elucidated. Hispanic Americans are the second largest and fastest growing ethnic group in the US. In the near future we will witness an increase in the prevalence of diabetes in the US population of much larger proportion than what has been observed far [6]
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