The validity of dietary assessment in general practice

Objective-To validate a range of dietary assessment instruments in general practice. Methods-Using a randomised block design, brief assessment instruments and m ore complex conventional dietary assessment tools were compared with an acc epted "relative" standard-a seven day weighed dietary record. The standard was checked using biomarkers, and by performing test-retest reliability in additional subjects (n=29). Outcomes-Agreement with weighed record. Percentage agreement with weighed r ecord, rank correlation from scatter plot, rank correlation from Bland-Altm an plot. Reliability of the weighed record. Setting-Practice nurse treatment room in a single suburban general practice . Subjects-Patients with risk factors for cardiovascular disease (n=61) or ag e/sex stratified general population group (n=50). Results-Brief self completion dietary assessment tools based on food groups eaten during a week show reasonable agreement with the relative standard. For % energy from fat and saturated fat, non-starch polysaccharide, grams o f fruit and vegetables and starchy foods consumed the range of agreement wi th the standard was: median % difference -6% to 12%, rank correlation 0.5 t o 0.6. This agreement is of a similar order to the reliability of the weigh ed record, as good as or better than test standard agreement for more time consuming instruments, and compares favourably with research instruments va lidated in other settings. Underreporting of energy intake was common (40%) and more likely if subjects were obese (body mass idex (BMI) greater than or equal to 30 60% under-reported; BMI <30 29%, p<0.001). Conclusion-Under-reporting of absolute energy intake is common, particularl y among obese patients. Simple self assessment tools based on food groups, designed for practice nurse dietary assessment, show acceptable agreement w ith a standard, and suggest such tools are sufficiently accurate for clinic al work, research, and possibly population dietary monitoring.