Metabolizable energy of macronutrients.

I describe recent advances in assessing the amount of energy available from diets of varied composition. Empirical models of food energy prediction have grown in preference to factorial models over the past 20 y and knowledge of the quantitative aspects of energy salvage in the colon have modified our thoughts on how to best calculate food energy values. In contrast, food regulatory practices have been limited mostly to changes in the way in which carbohydrate is defined or measured and there has been little change in the basic approach to energy evaluation or the energy conversion factors used with food components. The empirical systems have advantages over factorial models of food energy assessment and it is proposed that such empirical systems should be used in food regulations, food tables and databases, and in nutritional studies in which knowledge of metabolizable energy intake is desirable but cannot be determined directly.