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close this bookEnergy and Protein requirements, Proceedings of an IDECG workshop, November 1994, London, UK, Supplement of the European Journal of Clinical Nutrition (International Dietary Energy Consultative Group - IDECG, 1994, 198 pages)
close this folderEnergy requirements of older individuals
View the document(introductory text...)
View the documentIntroduction
View the documentMethodology for determination of total energy expenditure
View the documentTotal energy expenditure of older individuals
View the documentRelationship between total energy expenditure and physical activity
View the documentEffects of energy balance on nitrogen balance
View the documentSummary of energy requirements in older individuals and recommendations for future research
View the documentReferences
View the documentDiscussion

Effects of energy balance on nitrogen balance

Reliable measurement and knowledge of energy requirements of the elderly is essential to the accurate determination of protein requirements. Negative energy balance results in negative N balance (because lean tissue is mobilized along with fat and glycogen), and positive energy balance promotes positive N balance. A summary of data from several N balance studies by Pellett & Young (1992) indicated that even very small discrepancies in energy balance can have a major impact on the outcome of N balance: an energy imbalance of only 1 kcal/kg changes N balance by 1 mg/kg. It is not possible to measure the energy balance of individual subjects to 65 kcal/d in short-term studies ( < 30 days), which means that data on N balance from individual subjects should not be used to judge the adequacy of protein intake. Such data can only be used as the average of groups in which small variations in energy intake above and below actual energy expenditure can be expected to cancel out. Because energy requirements may have been underestimated in many previous studies, there is a potential bias towards overestimation of protein requirements in N balance experiments in older subjects.