The Role of Insulin Sensitivity in Lean Mass Changes During Weight Loss With or Without Exercise

This study aimed to investigate the association between baseline insulin sensitivity (SI) and changes in total lean mass (LM) and appendicular LM (ALM) during a diet-induced weight loss program with or without exercise. We conducted a secondary data analysis from a controlled weight loss study in premenopausal women with overweight aged 21-41. Women were randomized into three groups: diet-only, diet plus aerobic exercise, or diet plus resistance exercise. Body composition was assessed using dual-absorptiometry X-ray and SI using an intravenous glucose tolerance test. Multiple linear regression was used to determine if baseline SI was predictive of changes in total LM and ALM. There were significant group-SI interactions on changes in total LM (β = 0.474, p = 0.003, adjusted r2 = 0.371) and ALM (β = 0 0.462, p = 0.009, adjusted r2 = 0.231) after adjusting for covariates, indicating that greater baseline SI was associated with less LM loss only in women who did not exercise. Higher baseline SI is associated with greater retention of LM when weight loss is induced with diet alone, but not when exercise (aerobic or resistance) is included. This reinforces the importance of including exercise in all weight loss interventions. ClinicalTrials.gov identifier: NCT00067873.