Urine nitrogen as an independent validatory measure of dietary intake: a study of nitrogen balance in individuals consuming their normal diet.
In order to determine the value of 24 h urine nitrogen (N) excretion as a way of validating dietary methods of measuring protein intake in individuals, daily N intake and excretion has been measured in eight healthy subjects while consuming their usual, varying, diets for 28 days. Daily duplicates of all food eaten were obtained and consecutive 24 h collections of urine and feces were made throughout and analyzed for N by the Kjeldahl method. The completeness of the 24 h urine collections was verified by the use of PABA and of feces by radiopaque pellets. N losses in blood and from the skin were measured. The within person variation in dietary intake ranged from 14 to 26% (coefficient of variation, CV) while urine N was more constant, varying from 11 to 18% (CV) within individuals. In these subjects eight 24 h urine collections, verified for their completeness, were sufficient to estimate dietary N intake to within 81 +/- 5% (SD) as assessed by 18 day dietary records.
D000328:Adult; D003404:Creatinine / Q000652:urine; D004034:Diet Surveys; D004044:Dietary Proteins / Q000008:administration & dosage*; D005243:Feces / Q000032:analysis; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009584:Nitrogen / Q000008:administration & dosage / Q000378:metabolism / Q000652:urine*; D005082:Physical Exertion; D012867:Skin / Q000378:metabolism; D013997:Time Factors
D004044:Dietary Proteins; D003404:Creatinine; D009584:Nitrogen