In Australia, the process by which food energy factors are derived for food labelling purposes is under review. One of the questions of international relevance is whether energy factors should be derived using a definition of metabolisable energy (ME) or a definition of net (metabolisable) energy (NME), or some mixture of the two. ME describes the food energy available for heat production and body gains. NME deducts obligatory thermogenesis from ME in an attempt to reflect the food energy that can be converted to ATP energy within the body. Some countries use NME to derive energy factors for novel food ingredients such as sugar alcohols and polydextrose, but continue to use ME for protein, fat, carbohydrate, and alcohol. The present paper puts a case for using a consistent system (ME at the present time) for all food components. Reasons for this include: consistent application to all food components allows valid comparisons between products; food energy values and estimates of energy expenditure (food energy requirements) should be directly comparable; NME does not account for all sources of thermogenesis; differences between ME and NME for sugar alcohols and polydextrose are small in the context of the whole diet; and the ME system does not preclude information about metabolic efficiency being provided as additional information. Any major change to the way in which energy values are expressed (e.g. global adoption of the NME system) merits wide discussion among the human nutrition community. One aim of this present paper is to stimulate this discussion.