The incidence and prevalence of pre-diabetes and type 2 diabetes in adolescents in the USA is increasing, and is disproportionately higher in Hispanics and African Americans.
Although the exact cause for this increase is not known, it is clear that it is related to the concomitant increase in obesity. However, why some obese subjects develop pre-diabetes and diabetes, while others do not, is yet to be established. In addition, the rise in the prevalence of obesity in children is associated with the emergence of fatty liver disease early in life, for which there is a clear ethnic disparity, with lower levels in African Americans and higher levels in Hispanics. Two predominant paradigms, both based on an abnormal accumulation of body fat, have been used to explain the reasons why some obese subjects develop pre-diabetes, diabetes and fatty liver disease, while others do not.
First, is the portal/visceral hypothesis, which suggests an abnormal accumulation of visceral adipose tissue; and, second, is the ectopic fat storage hypothesis, which suggests an abnormal accumulation of ectopic fat in liver, skeletal muscle and pancreas. In this protocol, we will measure intraabdominal, subcutaneous abdominal, hepatic and pancreatic fat accumulation in Hispanic and African American youth and adolescents who are either at risk for overweight or overweight (At or above the 85th CDC age and gender specific BMI percentile) with normal glucose tolerance, or obese with impaired glucose tolerance (IGT). Regional fat deposition and composition will be assessed using state-of-the-art magnetic resonance imaging. We will also employ high-resolution ultrasound to measure carotid intimamedial thickness as a surrogate for vascular fat deposition and for the risk of CVD in these populations.
Our hypotheses are: 1) Fat deposition (intraabdominal, hepatic, pancreatic and muscular fat) and measures of carotid wall thickness will increase with degree of disease progression (at risk for overweight to overweight to pre-diabetes); and, 2) Measures of fat deposition and composition at the various sites will allow the identification of unique fat phenotypes related to differences in disease risk between Hispanic and African American populations.