A diet history method for estimating energy and N intakes was validated against 24 h urinary N excretion and energy expenditure measured by the doubly-labelled water (DLW) method. Fortyeight women aged 50-65 years were studied over 1 year. Weighed diet records from 4 d and two 24 h urine collections, for measurement of urinary N excretion, were obtained in each of four seasons. At the end of the year, a diet history was obtained, BMR was measured by whole-body calorimetry, and, in sixteen women, total energy expenditure (EE) was measured by DLW. Energy intake (EI) and N intake (NI) were calculated using food tables. Using weighed records and diet history respectively mean NI were 11⋅21 (SD 2⋅09) g and 11⋅47 (SD 2⋅40) g (NS) and EI were 8⋅08 (SD 1⋅54) MJ and 8⋅20 (SD 1⋅86) MJ (NS). Mean urine N : NI and EI : BMR values indicated bias to under-reporting by weighed record and diet history techniques in some individuals, but there was no significant difference between these measures at the group level. The Pearson correlation coefficient (r) for urine N v. NI was 0⋅81 for the weighed record and 0⋅38 for the diet history. The correlation of EE v. EI was r 0⋅48 for weighed record and r 0⋅11 for diet history. In this study the diet history gave the same estimate of mean intake, but the weighed record appeared to perform better in ranking individuals.
Diet history: Diet record: ValidationThe diet history method of assessing dietary intake is favoured for two reasons. First, as a retrospective questionnaire method, it places less burden on subjects than do prospective diet records. Second, it is believed to obtain a better measure of long-term habitual intake than diet records, which, of necessity, record intake on a limited number of days. The debate over the respective merits of the weighed diet record and the diet history is a long one and many studies over several decades have compared their relative validity. On balance the diet history tends to obtain higher mean energy intakes (EI) (see reviews by Bingham, 1987;Black et al. 1991). However, without external validation such studies have been unable to reach a firm conclusion as to which, if either, is valid in absolute terms.A valid dietary assessment should give an estimate of mean intake that is close to the true intake and also be able to rank individuals correctly for intake within acceptable limits of precision. The two requirements do not necessarily go together. For example, a dataset of valid 24 h recalls would give a valid estimate of mean intake but could not rank individuals correctly for habitual intake. A diet record of sufficient length to measure habitual intake might rank individuals correctly but give an invalid estimate of mean intake due to systematic bias across all subjects. If random errors are large and if systematic bias is variable across individuals, then ranking will also be poor. Studies of relative validity indicate whether one method gives a higher intake than another, and comparison with expected energy requirements can help determine ...