VALIDATION OF WEIGHED RECORDS AND OTHER METHODS OF DIETARY ASSESSMENTUSING THE 24-H URINE NITROGEN TECHNIQUE AND OTHER BIOLOGICAL MARKERS

Results from analysis of 24 h urine collections, verified for complete ness with para-amino benzoic acid, and blood samples collected over 1 year were compared with 16 d weighed records of all food consumed coll ected over the year, and with results from 24 h recalls, food-frequenc y questionnaires and estimated food records in 160 women. Using the we ighed records, individuals were sorted into quintiles of the distribut ion of the urine N excretion:dietary N intake ratio (UN:DN). UN exceed ed DN in the top quintile of this ratio; mean ratio UN:DN = 1.13. Indi viduals in this top quintile were heavier, had significantly greater b ody mass indices, were reportedly more restrained eaters, had signific antly lower energy intake:basal metabolic rate ratios (EI:BMR), and ha d correlated ratios of UN:DN and EI:BMR (r -0.62). Those in the top qu intile reported lower intakes of energy and energy-yielding nutrients, Ca, fats, cakes, breakfast cereals, milk and sugars than individuals in the other quintiles but not lower intakes of non-starch polysacchar ides, vitamin C, vegetables, potatoes or meat. Correlations between di etary intake from weighed records and 24 h urine K were 0.74 and 0.82, and between dietary vitamin C and beta-carotene and plasma vitamin C and beta-carotene 0.86 and 0.48. Correlations between dietary N intake from weighed records and 24 h urine excretion were high (0.78-0.87). Those between N from estimated food records and urine N were r 0.60-0. 70. Correlations between urine N and 24 h recalls and food-frequency q uestionnaires were in the order of 0.01 to 0.5. Despite problems of un derreporting in overweight individuals in 20% of this sample, weighed records remained the most accurate method of dietary assessment, and o nly an estimated 7 d diary was able to approach this accuracy.