| dc.description.abstract | Adolescence proves to be one of the most vulnerable development stages in the life of humans and therefore dietary assessment of this group is important, but complex. This is due to rapid growth during puberty and the development of new eating patterns that influence dietary intake. Adequate dietary intake in this age group is crucial, since adverse effects such as iron deficiency anemia, inadequate growth and dental caries can occur. Furthermore, dietary imbalance is a significant risk factor that can lay the groundwork for developing preventable complications in late adolescence and adult life such as non-communicable chronic diseases including obesity and diabetes mellitus type II and certain cancers, all leading causes of morbidity and mortality. Given the vulnerability of adolescents in terms of dietary intake, understanding their dietary intake is crucial. Dietary assessment of adolescents is influenced by social, physiological and psychological changes making accurate measurement of this group difficult. Hence, it is of fundamental importance to find a golden standard in terms of a dietary assessment method to use in this group. Several international studies investigated validity and reproducibility of the dietary intake of adolescents, measured with different dietary assessment methods. However, in South Africa only three validity and reproducibility studies have been published and none of them focused exclusively on adolescents. Since the validity of the results of dietary assessment methods of international studies cannot be extrapolated to South African black adolescents, this study emanated from the need to investigate whether multiple 24-hour recalls are valid and reproducible when used to assess the dietary intakes of black adolescents in a convenience sample of grade eight learners from a high school in a township in the North West Province. The study was nested in the multidisciplinary "Physical, Activity in the Young" (PLAY) study. Firstly, the optimal number of 24-hour recalls was determined by calculation of reproducibility coefficients for energy, selected nutrients and food groups. Results showed that four repeated 24-hour recalls provided the optimal reproducibility for black peri-urban South African adolescents. Secondly, the search for a reference method to compare energy intake against energy expenditure led to an investigation into basal metabolic rate equations and physical activity factors with the intention of estimating the energy expenditure. Validity of reported energy intake assessed by multiple 24-hour recalls and estimated energy expenditure was tested using the Pearson correlation coefficient and the dependent t-test. The Pearson correlation test revealed low associations between energy intake and energy expenditure for boys (0.32) and girls (0.17), while the dependent t-test of the energy intake between the different measured occasions showed little difference, which could be explained by the high within participant variation and lower variation between the different participants. The low correlation coefficients showed that there was no association between reported energy intake and mean estimated energy expenditure; thus also no agreement. As a result, multiple 24-hour recalls measured over two years with only five 24-hour recalls did not give a valid measurement of the energy intake of black peri-urban adolescents.
Lastly, the ratio of reported energy intake over energy expenditure was evaluated against the energy cut-off points, specifically calculated for age and ethnic group. It indicated that 85% of the participants underreported their energy intake. These results could have been influenced by the estimated basal metabolic rate equations that could have estimated the basal metabolic rate of this group incorrectly or could be due to the inability of the group to recall their physical activity levels correctly. Therefore it is recommended that further validity studies regarding dietary intake need to be performed on adolescents. It is suggested that energy expenditure as a reference method should be measured by using a calorimeter or the doubly labeled water method and then compared with the reported energy intake. Analysing different biochemical determinants of nutritional intake could also be used as an objective reference method to assess the validity of dietary data obtained from questionnaires. | en_US |
