Production of energy from food is a complex process. Process of eating food is known as ingestion. Then, this complex food material is broke down into simple nutrients through the process of digestion. Those simple nutreints (glucose, vitamin, etc.) are then absorbed by cell in the inner linning of intestine and the process is called assimilation and get distributed to different parts of the body. Glucose is then broke down into pyruvate in cytoplasm generating small amount of energy (ATP) via glycolysis process. Pyruvate, again is further broke down to produce more energy. This process is called Krebs cycle.