Hormonal

Higher baseline insulin sensitivity is associated with greater retention of lean mass during diet-induced weight loss, but this protective effect is nullified when aerobic or resistance exercise is included in the intervention.

If you are losing weight through diet alone, your metabolic health (insulin sensitivity) dictates how much muscle you keep; those with better sensitivity lose less muscle. However, if you add exercise (especially resistance training), your baseline insulin sensitivity no longer matters for muscle preservation. Exercise protects muscle mass regardless of your metabolic profile, making it the most reliable tool for preserving lean mass during weight loss.