Repeated measurement of habitual food intake increases under-reporting andinduces selective under-reporting

The aim of the current study was to measure differences in reporting behavi our between a first occasion of 7 d food recording and a second occasion of 7 d food recording 12 weeks later, in a group of elderly men (n 17) and wo men (n 17). Half the group followed an exercise intervention. The mean age was 61 (SD 5) years and mean BMI was 26.2 (SD 38)kg/m(2). Reported energy i ntake was compared with energy expenditure as calculated from measured BMR and physical activity assessed with a tri-axial accelerometer for movement registration. Total under-reporting was divided into undereating and under- recording. Undereating was calculated from the change in body mass over the recording week and the under-recording was measured using the water balanc e technique. In the first period, the total under-reporting was 21% and inc reased to 27% in the second period (P = 0.03). In the first period there wa s no indication for subjects eating less during the recording week, however , in the second period subjects lost body mass during the food recording in dicating undereating. The amount of under-recording was calculated at 21% i n the first period and 18% in the second period of recording (P 0.28). Duri ng the second period subjects selectively under-reported their fat intake a nd over-reported their protein intake. In conclusion, repeated assessment o f food intake caused a higher quantitative and a qualitative under-reportin g of food intake. The effect of interventions (dietary or otherwise) on hab itual food intake might be confounded by changes in food-reporting behaviou r.