Dietary intake reports fidelity--fact or fiction?

Bias is common in the assessment of self-reported dietary intake and physical activity. Little is known about the reasons for this underreporting, which is obtained even from rural individuals and lean subjects.

Healthy volunteers (16 males, aged 18-55 years) were given two different full diets (high and low in saturated fat), each for a period of 4 weeks.

The subjects were able to provide a report of their dietary intake with relatively high accuracy (68.4%) on day one. Accuracy declined on day two (64.2%), and on day three, the reporting accuracy was only 55.0% (p<0.05). Interestingly, on day one, individuals were more precise (p<0.05) in their dietary reports if they had consumed an unhealthy diet high in saturated fat (72.5%) than a healthy diet high in unsaturated fat (64.4%). The most frequently omitted items were fruits and vegetables. The non-reporting of food items consumed is very high, even in the short term, and individuals tend to remember unhealthy items better.

Our pilot study showed that the inaccuracy of self-reported data includes not only the underestimation of energy intake (portion size) but also inaccurate qualitative data.