To evaluate the validity of food photographs used to support the reporting of food intake with an FFQ designed for adolescents from Rio de Janeiro, Brazil.

A set of ninety-five food photographs was elaborated. The photographs’ evaluation process included the acknowledgement of foods and portions in the pictures. In the identification of foods (ninety-five photographs) and typical portions (twelve photographs), the adolescents were requested to answer a structured questionnaire related to the food photographs. The identification of the portion size of amorphous foods (forty-three photographs) was performed using three different portion sizes of actual preparations. The proportions (and 95 % confidence intervals) of adolescents who correctly identified foods and portion size in each photograph were estimated.

A public school in Niterói, Rio de Janeiro State, Brazil.

Sixty-two adolescents between 11·0 and 18·9 years old, randomly selected.

At least 90 % of adolescents correctly identified the food in ninety-two photographs and the food in the three remaining photographs was recognized by 80–89 % of the adolescents. At least 98 % of the adolescents correctly identified eleven typical or natural portions in the food photographs. For amorphous foods, at least 70 % of teenagers correctly identified the portion size in the photograph of thirty-one foods; for the other photographs, the portion size was correctly recognized by 50–69 % of the adolescents for eight foods and by less than 50 % of adolescents for four foods.

The analysed photographs are appropriate visual aids to the reporting of food consumption by adolescents.

To test the effect of image size and presence of size cues on the accuracy of portion size estimation by children.

Children were randomly assigned to seeing images with or without food size cues (utensils and checked tablecloth) and were presented with sixteen food models (foods commonly eaten by children) in varying portion sizes, one at a time. They estimated each food model’s portion size by selecting a digital food image. The same food images were presented in two ways: (i) as small, graduated portion size images all on one screen or (ii) by scrolling across large, graduated portion size images, one per sequential screen.

Laboratory-based with computer and food models.

Volunteer multi-ethnic sample of 120 children, equally distributed by gender and ages (8 to 13 years) in 2008–2009.

Average percentage of correctly classified foods was 60·3 %. There were no differences in accuracy by any design factor or demographic characteristic. Multiple small pictures on the screen at once took half the time to estimate portion size compared with scrolling through large pictures. Larger pictures had more overestimation of size.

Multiple images of successively larger portion sizes of a food on one computer screen facilitated quicker portion size responses with no decrease in accuracy. This is the method of choice for portion size estimation on a computer.