Validation of a dietary record system for the estimation of daily cholesterol intake in individual outpatients.

In order to develop a reliable system for measuring daily cholesterol intake in individual outpatients, studies were undertaken to establish the shortest time period (in days) for which it is necessary to obtain daily food intake records. Three volunteers were trained in dietary record-keeping and portion-size assessment, and instructed to self-select a low-cholesterol diet for 20 days. During the study period they maintained daily dietary records and collected dummy diets. Comparisons of cholesterol intake calculated from the dietary records (mean 144 mg/day, SD +/- 13, n = 60) to the values from chemical analysis (118 +/- 28 mg/day) demonstrated that the calculated values were higher (mean 19%). More importantly, it was found that a minimum of 9 days' records of dummy diet analyses were required in order to reach an estimate of daily cholesterol intake that varied by less than 10% from the mean of the 20-days' values. In 100 outpatients trained to adhere to a moderately low-cholesterol intake and who maintained sequential dietary records for 9 days, it was found that the mean daily intake was 251 mg/day but that individual patients exhibited substantial daily variations in cholesterol intake (average coefficient of variation = 54%, range = 8.5 to 121.2%). These results demonstrate that, under conditions of training in dietary record-keeping and portion-size assessment, adherence to a low-cholesterol diet, and with collection of at least 9 days of dietary records, a reliable quantitative estimate of daily dietary cholesterol intake can be obtained in free-living outpatient populations.