Rand W M, Scrimshaw N S, Young V R
Am J Clin Nutr. 1979 Jul;32(7):1408-14. doi: 10.1093/ajcn/32.7.1408.
The temporal pattern of daily urinary nitrogen (UN) excretion was investigated in 21 young adult men and women who participated in two metabolic studies involving constant diets and lasting 8 to 11 weeks. For one group (16 subjects), nitrogen (N) intake was about 280 mg N/kg per day (mixed animal and plant protein sources) for 8 weeks; for the second group (five subjects), N intake was about 90 mg N/kg per day (egg protein) for 11 weeks. Two mathematical models were examined to determine how well they described the variations in UN. The first modeled only random variability while the second added a component of serial correlation (correlation between successive daily observations). After correcting the UN data for linear trend, to minimize effects of possible alterations in body composition, only two of the 21 subjects showed significant serial correlation of daily UN. Moreover, it is shown that any serial correlation undetectable in these data would not be of practical importance in estimating UN levels in short-term dietary experiments. It is concluded that the interpretation of metabolic N balance measurements involving constant N intakes over relatively short dietary periods in not complicated by cyclic, time-dependent variations in UN.
对21名年轻成年男性和女性的每日尿氮（UN）排泄的时间模式进行了研究，这些人参与了两项涉及固定饮食且持续8至11周的代谢研究。对于一组（16名受试者），8周内氮（N）摄入量约为每天280毫克氮/千克（动植物蛋白混合来源）；对于第二组（5名受试者），11周内氮摄入量约为每天90毫克氮/千克（鸡蛋蛋白）。研究了两个数学模型，以确定它们对UN变化的描述程度。第一个模型仅模拟随机变异性，而第二个模型增加了序列相关性成分（连续每日观察值之间的相关性）。在对UN数据进行线性趋势校正后，为尽量减少身体成分可能变化的影响，21名受试者中只有2名显示出每日UN的显著序列相关性。此外，研究表明，这些数据中任何未检测到的序列相关性在短期饮食实验中估计UN水平时都不具有实际重要性。得出的结论是，在相对较短的饮食期内涉及固定氮摄入量的代谢氮平衡测量结果的解释不会因UN的周期性、时间依赖性变化而变得复杂。
