Understanding the Engine Inside You In Brief Metabolism = your body’s energy engine; it adapts to habits. Track weekly trends: weight, body comp, resting HR, sleep, intake. Support it: strength training, protein, sleep, stress control, hydration. Adjust slowly: change one variable at a time for 2–3 weeks. Most men think of metabolism as a mysterious switch that determines whether you stay lean or gain weight — something that either works in your favor or doesn’t. But metabolism isn’t a fixed setting. It’s an intricate, adaptive system — your body’s internal engine that runs everything from breathing and digestion to muscle repair and energy production.