Where does the energy for human metabolism come from

From food

Explanation:

Food energy is a chemical energy used by humans through the process of cellular respiration. Food contain macromolecules such as lipids, proteins, carbohydrates, water, vitamins, and minerals that are necessary for the human metabolism and they are broken down and used by the series of metabolic steps (glycolysis, Krebs  cycle, electront transport chain and oxidative phosphorilation). Digested macromolecules should be used either as a source of energy or as building blocks for the cell.

At the end of catabolic processes within an organism food energy is transformed into energy usable by the cell-ATP.