Protein, amino acid metabolism and therapy: Edited by Erich Roth and Paul B. PencharzEvidence that protein requirements have been significantly underestimatedElango, Rajavela,b; Humayun, Mohammad Aa,b; Ball, Ronald Oa,b,d; Pencharz, Paul Ba,b,c,dAuthor Information aThe Research Institute, The Hospital for Sick Children, Toronto, Canada bDepartment of Nutritional Sciences, Canada cDepartment of Paediatrics, University of Toronto, Ontario, Canada dDepartment of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada Correspondence to Dr Paul B. Pencharz, MB, ChB, PhD, Division of Gastroenterology, Hepatology and Nutrition, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada Tel: +1 416 813 7733; fax: +1 416 813 4972; e-mail: [email protected] Current Opinion in Clinical Nutrition and Metabolic Care: January 2010 - Volume 13 - Issue 1 - p 52-57 doi: 10.1097/MCO.0b013e328332f9b7 Buy Metrics Abstract Purpose of review This review discusses recent evidence that suggests a significant underestimation of protein requirements in adult humans. Recent findings Traditionally, total protein requirements for humans have been determined using nitrogen balance. The recent Dietary Reference Intake recommendations for mean and population-safe intakes of 0.66 and 0.8 g/kg/day, respectively, of high-quality protein in adult humans are based on a meta-analysis of nitrogen balance studies using single linear regression analysis. We reanalyzed existing nitrogen balance studies using two-phase linear regression analysis and obtained mean and safe protein requirements of 0.91 and 0.99 g/kg/day, respectively. The two-phase linear regression analysis is considered more appropriate for biological analysis of dose–response curves. Considering the inherent problems associated with the nitrogen balance method, we developed an alternative method, the indicator amino acid oxidation technique, to determine protein requirements The mean and population-safe requirements in adult men were determined to be 0.93 and 1.2 g/kg/day and are 41 and 50%, respectively, higher than the current Dietary Reference Intakes recommendations. Summary The indicator amino acid oxidation-based requirement values of 0.93 and 1.2 g protein/kg/day and the reanalysis of existing nitrogen balance studies are significantly higher than current recommendations. Therefore, there is an urgent need to reassess recommendations for protein intake in adult humans. © 2010 Lippincott Williams & Wilkins, Inc.