Under-reporting of energy intake affects estimates of nutrient intakes

Under-reporting of energy intake is a common problem in nutritional epidemiological studies. The aim of the present study was to determine the effect of under-reporting of energy intake on the estimates of nutrient intakes. In this cross-sectional study, 901 subjects aged >16 y were randomly selected from participants of the Tehran Lipid and Glucose Study. Dietary intake was assessed by means of two 24-hour dietary recalls. Basal metabolic rate (BMR) was determined according to age, sex and weight. The ratio of energy intake (EI) to BMR was calculated. Under-reporting of energy intake was defined as EI:BMR< 1.35 and normal-reporting of dietary intake as EI:BMR = 1.35-2.39. To obtain energy-adjusted amounts of macro- and micronutrients, the residual method was used. Under-reporting of energy intake was revealed in 31% of the subjects and was more common among females (40%) than males (19%, P <0.01). The mean age of females who under-reported was significantly lower than the normal-reporting females (32 +/- 13 vs. 35 +/- 14 y, P <0.05); however, the age difference between the two groups was not significant in men. Under-reporters had higher BMIs compared to normal-reporters in both genders. The absolute intakes of macro- and micronutrients (except for B12 in females and B6 and zinc in both genders) were lower in under-reporters, but following adjustment, no significant differences were seen. The results have revealed that under-reporting of energy intake affects the estimates of nutrient intakes; thus in studies aimed at determining the association between a certain chronic disease and a nutrient intake, we suggest adjustments be made for energy intake.