Food energy values of artificial feeds for man

The gross and metabolizable energy values of artificial enteral and parenteral feeds have been calculated from detailed composition data for amino acid, fatty acid, saccharide and other oxidizable substrates and compared with similar values calculated for conventional foods. The background to the derivation and application of calorie conversion factors is briefly reviewed. There is evidence of widespread inappropriate application of calorie conversion factors for carbohydrates and amino acid mixtures. Appropriate digestibility or availability factors for the oxidizable fractions of artificial feeds is discussed for normal adult man and the intrinsic difficulty of obtaining availability values for subjects with varying types of malabsorption or urinary and tissue losses is emphasized. The nitrogen:protein conversion ratio and the availability of energy at a biochemical level (i.e. net ATP yield per calorie) is also considered. Finally, a more uniform and appropriate approach to calculating energy values for artificial feeds for the purposes of labelling, product description and estimating energy intake of patients is called for.