In the United States, Black Americans are largely descendants of West
African slaves; they have a higher relative proportion of obesity and experience
a higher prevalence of diabetes than White Americans. However,
obesity rates alone cannot explain the higher prevalence of type 2 diabetes.
Type 2 diabetes is characterized by insulin resistance and beta-cell dysfunction.
We hypothesize that the higher prevalence of type 2 diabetes in African
Americans (as compared to White Americans) is facilitated by an inherited
higher percentage of skeletal muscle fibre type II and a lower percentage of
skeletal muscle fibre type I. Skeletal muscle fibre type II is less oxidative and
more glycolytic than skeletal muscle fibre type I. Lower oxidative capacity is
associated with lower fat oxidation and a higher disposal of lipids, which are
stored as muscular adipose tissue in higher amounts in Black compared to
White Americans. In physically active individuals, the influence of muscle
fibre composition will not be as detrimental as in physically inactive individuals.
This discrepancy is caused by the plasticity in the skeletal muscle
fibre characteristics towards a higher activity of oxidative enzymes as a
consequence of physical activity. We suggest that a higher percentage of
skeletal muscle fibre type II combined with physical inactivity has an impact
on insulin sensitivity and high prevalence of type 2 diabetes in Blacks of West
African ancestry.