Adipose tissue in muscle: A novel depot similar in size to visceral adipose tissue

Background: The manner in which fat depot volumes and distributions, particularly the adipose tissue (AT) between the muscles, vary by race is unknown. Objective: The objective was to quantify a previously unstudied and novel intermuscular AT (IMAT) depot and subcutaneous AT, visceral AT (VAT), and total-body skeletal muscle mass in healthy sedentary African American (AA), Asian, and white adults by whole-body magnetic resonance imaging. IMAT is the AT between muscles and within the boundary of the muscle fascia. Design: Analyses were conducted on 227 women [AA (n = 79): body mass index (BMI; in kg/m ²), 29.0 ± 5.5; age, 45.7 ± 16.9 y; Asian (n = 38): BMI, 21.7 ± 2.9; age, 47.2 ± 19.9 y; whites (n = 110): BMI, 24.9 ± 5.4; age, 43.7 ± 16.2 y]) and 111 men [AA (n = 39): BMI, 25.6 ± 3.2; age, 45.5 ± 18.8 y; Asian (n = 13): BMI, 24.9 ± 2.5; age, 45.6 ± 25.0 y; white (n = 59): BMI, 25.8 ± 3.8; age 44.5 ± 16.3 y]. Results: IMAT depots were not significantly different in size between race groups at low levels of adiposity; however, with increasing adiposity, AAs had a significantly greater increment in the proportion of total AT (TAT) than did the whites and Asians (58, 46, and 44 g IMAT/kg TAT, respectively; P = 0.001). VAT depots were not significantly different in size at low levels of adiposity but, with increasing adiposity, VAT accumulation was greater than IMAT accumulation in the Asians and whites; no significant differences were observed in AAs. Conclusion: Race differences in AT distribution extend to IMAT, a depot that may influence race-ethnicity differences in dysglycemia.