Improvement of Dietary Assessment among Adolescents

Background: Collecting information on food and dietary intake provides valuable insights into the associations between diet and health and helps to evaluate the impact of intervention programmes. Measuring dietary intake is challenging, particular when adolescents are the target group. Errors associated with the quantification of food portion size (FPS) are the most common errors to arise when assessing dietary intake. Aims: To improve the measurement of adolescents’ dietary intake by investigating certain variables related to adolescents’ FPSs, and developing and validating an online 24-hour dietary assessment tool (myfood24) based on adolescents’ (11-18 years old) needs and preferences. Methodology: In the first part of the thesis, the UK National Diet and Nutritional Survey (NDNS 2008-2011) was used to investigate adolescents’ FPSs, to identify differences in FPS between adolescents and adults (19-65y), and to investigate the relationship between adolescents’ FPS and BMI. The second part was a collaborative project to develop myfood24, a new web-based dietary assessment tool. I was responsible for ensuring fit for purpose for adolescents. A multi-stage process was used to facilitate this. It comprised of focus groups, usability and acceptability studies, and evaluation of the relative-validity of myfood24 among adolescents. Results: FPS differed by age group more than it did by gender, and older adolescents (15-18y) had slightly larger FPSs than younger adolescents (11-14y). Differences were more noticeable for beverages than for food items. Some significant differences were found in FPS between adolescents and adults, although the differences were small in terms of weight. The top ten contributing foods towards adolescents’ daily EI can be defined as high-energy-dense foods. Portion sizes of a number of high-energy-dense foods were found to be positively associated with BMI, when eliminating the effect of underreporting EI. Involving adolescents in the development process of myfood24 enhanced the overall acceptability and usability of myfood24. Following improvements, the average system usability score (SUS) of myfood24 was 74/100 and the mean completion time was 16 minutes. There was no significant bias identified when comparing myfood24 with an interviewer-administered multiple-pass recall for EI and most reported nutrients. The mean difference between myfood24 and the interviewer (MPR) was small, -55 kcal (-230kJ) (95% CI: -117, 7 kcal, (-490 to 30 kJ); P=0.4) for EI. There were strong intraclass correlation coefficients (ICCs) for EI and most reported nutrients. Conclusion: FPS increased by age and there was some disparity between adolescents and adults in FPSs. However, the magnitude of the differences was small. The portion sizes of a limited number of high-energy-dense foods were found to be associated with a higher BMI in all adolescents. However, when eliminating the effect of under-reporting, portion sizes of a number of high-energy-dense foods were associated with a higher BMI. myfood24 is an appropriate, reliable and easy to use dietary assessment tool for adolescents (11-18y). It has the potential to collect dietary data of comparable quality to that of an interviewer-administered multiple-pass recall. From a public health perspective, multiple approaches directed at adolescents to enhance their food choices and portion sizes of high-energy-dense foods are needed to prevent and control obesity and its related diseases.