From the small intestines, the digested food containing glucose, amino acids and fatty acids, etc, reaches the cells of the body by blood circulation. In cells these products are utilised to produce energy and also used for repair of the tissues themselves.
This becomes possible because of chemical reaction involving their oxidation. The reaction releases adequate energy for the use of living organisms. In other words, the oxidation of glucose and other carbohydrates releases energy and this process works with inhaled oxygen.