Assessing human energy and nutrient requirements has been a longstanding activity of FAO's Food and Nutrition Division and is considered an ongoing activity requiring continual review. Energy requirements need to be linked to the energy availability from foods, and this depends on knowing the amounts of energy-providing components in foods and expressing the energy values clearly and unambiguously. Because there are various methods of analysis of the macronutrient content in foods and numerous ways of expressing the energy values of foods there is a need to standardize and harmonise energy conversion values. This publication summarises the findings and recommendations of a workshop held in Rome in 2002 to review this issue.