A step towards using urinary nitrogen as a tool for validating 24-hour dietary recall interviews

In an active population, can urinary nitrogen output provide a satisfactory basis for estimating protein intake without preliminary screening to rule out metabolic disease? A successful demonstration would justify comparing average protein intake for active groups derived from 24-hour recall interviews with that obtained from 24-hour urine specimens. This could then be a practical test of the hypothesis that 24-hour recall data provide valid estimates for groups. Volunteers (45) from a university population limited their diet for four days to a commercially prepared liquid diet and provided a 24-hour urine specimen beginning on the morning of the fourth day. For men, average daily intake of protein was 112.8 grams and the estimated intake based on urinary nitrogen was 114.5. Corresponding data for women were 84.6 and 83.9. Screening for metabolic disease seems unnecessary but persons restricting their intake to less than their caloric needs will have their protein intake overestimated on the basis of urinary nitrogen measurement.