If you burned sugar or glucose outside of your body in the presence of oxygen, carbon dioxide, water and heat would be produced.

That heat is the energy released.

When you eat, say a potato, the carbohydrate is digested into glucose, the glucose then absorbed into the blood, carried to cells and also “burned” in the presence of oxygen (the breath you take in).

Similarly, carbon dioxide (out breath) and water are produced but instead of generating heat, the energy is stored in chemical bonds and held temporarily. Often for microsecond only, in a molecule called ATP. See infographic below.