Why just burning a food item provide information about its value as a portion of food the nutritional value of food can be measured on many different scales the most basic measurement scale is the free energy content of the food in other words how much energy is released when chemical bonds within the food are broken the energy content of food is measured in calories the amount of kinetic energy required to raise the temperature of 1ml of water one-degree food is burned under controlled conditions breaking chemical bonds and releasing free energy the burning is chemically similar to the breakdown of food in cellular respiration all over the process occurs much more quickly and in a less controlled fashion during a connection calorimeter can measure the energy and food but cannot measure the digested energy of what we have.