Some errors inherent in a longitudinal dietary survey revealed by the urine nitrogen test.
In the longitudinal population study 'Women in Gothenburg', subgroups of 154, 205 and 331 women in 1968/69, 1974/75 and 1980/81 respectively, were subjected to a dietary interview and collected a 24-h urine specimen for nitrogen analyses. The dietary data demonstrated a continuous increase in intake of energy and protein with time (2030, 2150 and 2350 kcal/d and 73, 77 and 90 g protein/d), while the 'true' protein intake (calculated from 24-h urine nitrogen) was unchanged (75, 73 and 75 g/d). The discrepancies were interpreted as being due to the changes in the dietary questionnaires made before the interviews in 1974/75, and again in 1980/81, changes expected to improve the method. In 1968/69 overweight women (BMI 24-30), as well as obese women (BMI greater than 30), reported a significantly smaller intake of energy and protein than lean women. Their reported protein intake was significantly lower than their 'true' protein intake (69 versus 77 g/d and 73 versus 94 g/d, respectively). Significant underreporting of dietary intake by the overweight and obese women in the studies 1974/75 and 1980/81 was revealed by the urine nitrogen test after correction for the methodological errors of the questionnaires. The results illustrate the necessity of using an independent validation test in dietary surveys.
Hultén
B
B
Department of Clinical Nutrition, Sahlgrenska Hospital, Gothenburg, Sweden.
Bengtsson
C
C
Isaksson
B
B
D000328:Adult; D000367:Age Factors; D000368:Aged; D015982:Bias; D001835:Body Weight; D003718:Denmark; D004034:Diet Surveys; D004044:Dietary Proteins / Q000032:analysis / Q000378:metabolism*; D004435:Eating; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine*; D009765:Obesity / Q000175:diagnosis* / Q000453:epidemiology / Q000652:urine; D011507:Proteinuria / Q000175:diagnosis; D013997:Time Factors
D004044:Dietary Proteins; D009584:Nitrogen