Skeletal muscle fat infiltration (known as myosteatosis) is greater in African compared with European ancestry men and may play an important role in the development of type 2 diabetes (T2D). However, prospective studies examining the magnitude of changes in myosteatosis with aging and their metabolic consequences are sparse.

Longitudinal changes in peripheral quantitative computed tomography measured calf myosteatosis [intermuscular fat (mm²) and skeletal muscle density as a measure of intramuscular fat (mg/cm³)] were examined in 1515 Afro‐Caribbean men aged 40+ years recruited without regard to their health status.

During an average of 6.2 years of follow‐up, an age‐related increase in intermuscular fat and a decrease in skeletal muscle density were observed (all P < 0.0001), which remained significant in those who lost weight, gained weight, or remained weight stable (all P < 0.0001). In addition, muscle density loss accelerated with increasing age (P < 0.0001). Increased intermuscular fat during follow‐up was associated with an increased incident risk of T2D independent of factors known to be associated with T2D (odds ratios per 1‐SD increase in intermuscular fat = 1.29; 95% CI = 1.08‐1.53).

Our findings suggest that both inter‐ and intramuscular fat increase with advancing age and that intermuscular fat contributes to development of T2D among African ancestry men.