The validation of energy and protein intakes by doubly labelled water and 24‐hour urinary nitrogen excretion in post‐obese subjects

The aim of the study was to validate three techniques of dietary assessment (weighed records, PETRA records and diet histories) in post‐obese subjects and to compare validation by doubly labelled water with validation against urinary nitrogen excretion. Eleven successful slimmers (one male and 10 females) kept weighed diet records for 21 days using both traditional scales (weighed record, WR) and the PETRA system of recording weight and food description on cassette tape; the changeover was on Day 11. Subjects were weighed on Days 1 and 21. Two diet histories (DH) were taken by different dietitians, one before and one after the study (DHA, DHB). Energy (EI) and nitrogen (NI) intakes were calculated from food tables. Total energy expenditure (TEE) was measured by the doubly labelled water method. Five 24 h urine collections validated by PABACHEK were obtained to measure urine N; seven individual collections with para‐amino‐benzoic acid (PABA) recovery $lt; 85% were rejected. Multiple regression analysis of WR and PETRA intakes showed no effect of survey method or order of survey, but significantly higher intakes on Friday to Sunday; mean intakes were adjusted to allow for variation in days of the week covered. Mean ± SD intakes from WR (7.10 ± 2.52 MJ, 10.32 ± 3.72 g N) and PETRA (7.22 ± 2.87 MJ, 10.37 ± 3.85 g N) were not significantly different. DHA estimated mean intakes lower (6.45 ± 2.66 MJ, 10.1 ± 3.2 g N) and DHB higher (7.79 ± 2.42 MJ, 11.9 ± 4.3 g N) than weighed methods, but not significantly. Reported 21‐day EI was 76% of measured TEE and urine N was 115% of diet N compared with the expected values of 100% and 82% for valid diet records indicating under‐reporting. Weight change, mean ‐ 0.75 (0.2 to ‐ 2.2) kg, suggested dieting during the recording period. Within subjects all methods tended to give similar results suggesting that personal factors strongly influence co‐operation. Copyright © 1995, Wiley Blackwell. All rights reserved