Heating of the body due to internal radioactivity. Heat energy produced from the assimilation or deamination of foods. The amount of potential energy added to the body as food. Heat increment is hard to measure. The values for the Heat Increments in the previous table are only for broad application.
Carbohydrates have a much higher Heat Increment.
Proteins have a Heat Increment somewhat higher than carbohydrates. It contains nitrogen in the form of amino acids. It's unavoidable because its in all food. It contains a different kind of energy. Animals need something to decrease their heat increment.