An evaluation of food photographs as a tool for quantifying food and nutrient intakes.

OBJECTIVE To evaluate the errors incurred by young adults using single portion size colour food photographs to quantify foods and nutrients consumed at six meals on two non-consecutive days. DESIGN Breakfast menus remained the same for the 2 days; but lunch and dinner menus varied. The amounts of food eaten by individuals were determined by weighing individual serving dishes pre- and post-consumption. The day after eating, all foods consumed were quantified in terms of fractions or multiples of the amounts shown in the food photographs. SUBJECTS Thirty adult volunteers (15 male, 15 female), aged 18-36 years, completed the protocol for day one; 27 (90%) completed day two. RESULTS Some foods were more difficult to quantify accurately than others. The largest error range was -38. 9% to +284.6% (cheese), whereas the smallest errors were incurred for juice (-21.5% to +34.6%, day one). All subjects who consumed muesli (day one) overestimated (+3.7% to +113.7%). No other foods were consistently over- or underestimated. For foods consumed at breakfast by the same subjects on both days, individual estimation errors were inconsistent in magnitude and/or direction. At the group level, most nutrients were estimated to within +/-10% of intake; exceptions were thiamin (+10.5%, day one) and vitamin E (-10.1%, day one; -15.3%, day two). Between 63% and 80% of subjects were correctly classified into tertiles on the basis of estimated intakes. CONCLUSIONS Despite some large food quantification errors, single portion size food photographs were effective when used to estimate nutrient intakes at the group level. It remains to be established whether, under the conditions used in this study, more photographs per food would improve estimates of nutrient intake at the individual level.