As you know, humans do not live by glucose alone, we need other nutrients we need to run our body normally. Accordingly the cells of the human body seethe with biochemical reactions, synthesizing one amino acid from another, making fats from carbohydrates, and channeling surplus organic molecules of all types into energy storage or release. There are two kinds of metabolic transformation in discuss the term of energy relate to the diet. They are the production of ATP from fats and proteins, and the synthesis of fats from high calorie foods.
First about the production of ATP from fats and proteins, we should reconsider first that even the leanest person has some fat in his body. During fasting or starvation, the body mobilizes these fats reserves for ATP synthesis, because even the bare maintenance of life requires a continous supply of ATP and seeking out new food sources demands even more energy. Fat metabolism flows directly into the pathways of glucose metabolism.