Muscle is the body's largest metabolic organ and the one most under your control. Building and repairing it is protein-limited — you need enough total protein, and the leucine within it, to trigger muscle protein synthesis — while vitamin D governs the contractile machinery and is reproducibly tied to strength and fall risk. Creatine refills the rapid-energy system for short bursts, magnesium guards against cramping, and iron delivers the oxygen working muscle demands. Muscle mass is now one of the strongest predictors of healthy aging, so this system is as much about longevity as performance. These 48 whole foods are ranked by how many of the key muscle nutrients a typical serving delivers (≥10% DV each).