A proxy approach to the determination of total caloric intake for use in cancer epidemiology

In the absence of complete dietary information on a cohort of 472 early-stage breast cancer patients a caloric prediction technique was developed. Deriving an accurate caloric denominator would enable examination of individual nutrient effects by controlling for potential confounding by calories. Surrogate measures of mean daily caloric intake were generated from estimates of basal metabolic rate (BMR) predicted from age, height, weight, and physical activity. A validation study was undertaken to test the relationship between the BMR proxy terms and mean daily energy intake obtained from four-day food diaries for 51 subjects. Pearson correlation coefficients between the diary-derived and predicted values of caloric intake were computed (r = 0.43, p = 0.001). The results are in the range of what many researchers found when comparing self-reports of total caloric intake in validation and reliability studies of various dietary assessment tools. Because of the large heterogeneity of results across the ages represented in this study (25-77 yrs), it is recommended that small validation studies of this type be carried out in the subpopulations of interest.