Objective: To investigate the degree of bias in under-reporting of food intake in obese and non-obese subjects, hypothesising that under-reporting may be selective for either macronutrient content (carbohydrate (CHO), fat, protein, alcohol), specific food types or eating occasions (meals, snacks).
Design: Thirty-three women (18 obese, 15 non-obese) were recruited to a long-stay metabolic facility for 24h. Ad libitum food intake was covertly measured throughout the study and a reported food intake completed at the end of 24h.
Results: Reported total daily energy intake was significantly lower than measured intake. Whilst meals were accurately reported, energy from snack foods eaten between meals was significantly under-reported. (P< 0.001) Reported total carbohydrate and added sugar intakes were significantly lower than measured, whilst reported protein and fat intakes were not significantly different from measured. Reported alcohol intake was also considerably lower than measured, but high variability prevented significance.
Conclusions: In both obese and non-obese women the major cause of under-reporting, as assessed by covert study design in subjects restricted within a metabolic facility, is the failure to report between-meal snack foods. There is some evidence for increased under-reporting in high CHO, but no evidence of a bias in under-reporting towards high fat or high protein foods.