Are the proposed limits of energy intake : basal metabolic rate and dietary nitrogen : urinary nitrogen ratios suitable for validation of food intake?

The validity of 7 d weighed records of diet obtained for pre-menopausal Mex ican women was assessed by two independent methods: the energy intake:BMR ( EI:BMR) and the dietary N:urinary N (DN:UN). For the latter, complete urine collections are required and completeness was assessed from measurements o f para-aminobenzoic acid (PABA) excretion. There were forty-six adult femal e subjects in the study, thirty-four were from Mexico City and twelve were from a rural population in the Central Highlands, Mexico. However, data wer e rejected from five urban women for whom the PABA excretion data suggested incomplete urine collection on four or more days. BMR was measured with Ox ylog portable O-2 consumption meters, and physical activity level was asses sed from a self-completed activity diary. An approximate relationship betwe en the EI:BMR ratio and the DN:UN ratio suggested that the rejection limits on the EI:BMR ratio recommended by are wider than the limits on the DN:UN ratio recommended by . Using the recommended cut-off points for EI:BMR but wider limits for DN:UN, twenty-one and twenty-five women respectively had a cceptable intake records by the two methods, and sixteen of them by both me thods. In conclusion the modification of the DN:UN limits to 0.92 and 1.70 to set acceptable intake values makes the use of measurements of N and ener gy balance comparable. Urine values with PABA recoveries greater than 100 /- 15 % should be rejected, as should UN values validated by less than 3 d.