Millward D J
Centre for Nutrition & Food Safety, School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey, United Kingdom.
Can J Appl Physiol. 2001;26 Suppl:S130-40. doi: 10.1139/h2001-048.
Protein intakes vary widely but costs and benefits of such variation is a long standing unresolved issue. The wide range of reported values for the minimum protein intake for N equilibrium in adults, i.e. 0.39 to 1.09 g/kg is best explained by an Adaptive Metabolic Demands model in which metabolic demands include amino acid oxidation at a rate varying with habitual protein intake and which changes slowly with dietary change. Thus within the reported data the true minimum requirement intake, the lowest values in the range at intakes approaching the Obligatory Nitrogen Loss, allows only fully adapted subjects to achieve N equilibrium. The higher values reflect incomplete adaptation. (13)C-1 leucine tracer balance studies of this model show (a) a fall with age in apparent protein requirements, (b) better than predicted efficiency of wheat protein utilization, and (c) controversially, lower lysine requirements than other workers, consistent with new evidence of de novo synthesis of lysine from urea salvaged by large bowel microflora. The main implication of the requirements model for athletes on high protein diets is increased exercise induced amino acid oxidation and risk of loss of body N when such high intakes are not maintained.
蛋白质摄入量差异很大，但这种差异的成本和益处是一个长期未解决的问题。成年人氮平衡的最低蛋白质摄入量报告值范围很广，即0.39至1.09克/千克，这最好用适应性代谢需求模型来解释，在该模型中，代谢需求包括氨基酸氧化速率，其随习惯蛋白质摄入量而变化，并随饮食变化而缓慢改变。因此，在报告的数据中，真正的最低需求摄入量，即在接近 obligatory Nitrogen Loss 的摄入量范围内的最低值，只允许完全适应的受试者实现氮平衡。较高的值反映了不完全适应。该模型的（13）C-1亮氨酸示踪剂平衡研究表明：（a）表观蛋白质需求随年龄下降；（b）小麦蛋白质利用率高于预测效率；（c）有争议的是，赖氨酸需求低于其他研究人员，这与大肠微生物群从尿素中重新合成赖氨酸的新证据一致。对于高蛋白饮食的运动员来说，需求模型的主要影响是，当不维持如此高的摄入量时，运动引起的氨基酸氧化增加以及身体氮流失的风险增加。
