What process does the body convert nutrients into fuel and is the sum of all chemical reactions?

Metabolism is the process where the body converts food/nutrients into fuel/energy to be used by the body cells for the daily activities, it also involves conversion of nutrients to materials for repair, growth, reproduction and repair.

Metabolism is divided into catabolism and anabolism where catabolism involves conversion of nutrients into energy and anabolism is the use of nutrients by the cell to repair and and build new tissues. Therefore, the answer is Metabolism.