For Students
Catabolism vs. anabolism: the basics of metabolism
Your metabolism runs on two opposing processes happening simultaneously, all day, every day.
Catabolism
Breaking larger molecules into smaller ones, releasing energy in the process. Digesting food, breaking down glycogen into glucose, and breaking down muscle protein into amino acids for fuel are all catabolic.
Anabolism
Building larger molecules from smaller ones, using energy in the process. Building muscle protein from amino acids and storing glucose as glycogen are both anabolic.
Both are happening constantly — the practical question for body composition is which one dominates over time. A calorie surplus with resistance training and adequate protein tends to favor net anabolism (muscle building); a calorie deficit tends to favor net catabolism (fat and, without enough protein and training stimulus, muscle breakdown). "Anabolic" and "catabolic" aren't good or bad on their own — they're just the two directions metabolism can run.
Keep reading: Body recomposition explained · Nitrogen balance explained · What is glycogen?