Atp

Metabolism is the sum of biochemical processes that convert food into ATP. Total daily energy expenditure has four components: BMR (60–70%, calculated with Mifflin-St Jeor), TEF (10%), NEAT (15–30%, 350–750 kcal/day variation — Levine 1999), and exercise. Lean mass is the primary driver of BMR. Metabolic adaptation (Leibel 1995: −250 kcal/day) explains why weight loss slows — and why understanding the physiology is essential for long-term management.