Sexual Dimorphism in the Relationship between Body Composition and Insulin Resistance in Older Adults

Epidemiological studies show an inconsistent relationship between lean mass and insulin resistance.

This study aimed to investigate the association between lean mass and insulin resistance in adults aged ∼60 to 80 y with and without obesity.

We analyzed data from the Pennington/Louisiana Nutrition and Obesity Research Center (NORC) biorepository and NHANES. Lean mass was represented as total lean mass, along with total lean mass and appendicular lean mass (ALM) adjusted for body weight (% lean mass and % ALM), and total lean mass and ALM adjusted for height (lean mass/ht² and ALM/ht²). We used partial correlation analyses to examine the relationship between insulin resistance (HOMA-IR) and body composition, and linear regression models to test for sex-by-body composition interactions.

In the NORC cohort with obesity, HOMA-IR positively correlated with total lean mass (r = 0.27, P = 0.005), lean mass/ht² (r = 0.30, P = 0.002), and ALM/ht² (r = 0.28, P = 0.004), only in females. In the NHANES cohort, HOMA-IR positively correlated with total lean mass (r = 0.23, P < 0.001), lean mass/ht² (r = 0.20, P < 0.001), and ALM/ht² (r = 0.14, P = 0.004) in females with obesity, and without obesity [total lean mass (r = 0.14, P = 0.001); lean mass/ht² (r = 0.18, P < 0.001); and ALM/ht² (r = 0.12, P = 0.005)]. In males, percent fat mass positively correlated with HOMA-IR in the NORC cohort with obesity (r = 0.27, P = 0.015) and in the NHANES cohort with obesity (r = 0.12, P = 0.043) and without obesity (r = 0.11, P = 0.005). Tests for interaction confirmed significant sex differences in the obesity cohorts for ALM/ht² (NORC: P = 0.011), % fat mass (NORC: P = 0.016; NHANES: P = 0.002), and total lean mass (NHANES: P = 0.001). In the NHANES nonobesity cohort, significant interactions were observed for lean mass/ht² (P = 0.001) and ALM/ht² (P = 0.005).

The relationship between body composition and insulin resistance displays sexual dimorphism. Although lean mass positively correlates with insulin resistance in females, in males, fat mass appears to be the dominant influence on insulin resistance.