Please read the abstract in the thesis. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Internal Medicine / unrestricted

The effect of nitrogen intake, nitrogen source, calorie intake, body weight, adaptation time, research group and sex on the nitrogen balance of human adults was investigated. Data from studies reported in the literature were combined and analyzed statistically by multiple regression techniques. Analyses were made separately for six sources of nitrogen: egg, beef, rice, corn, wheat and wheat gluten. Nitrogen intake, caloric intake and body weight exerted significant effects on nitrogen balance (5% level of confidence) for six, three and two of the six nitrogen sources, respectively. Other variables were not significant at the 5% level. Although differences were not significant (5% level), the correlation between nitrogen intake and nitrogen balance was greatest for four of the six nitrogen sources when data were expressed as grams per square meter of body surface area (g/m2) as opposed to when they were expressed per kilogram body weight or per kilogram raised to the 0.73 power. Curvilinear relationships between intake and balance in the submaintenance range of intakes were evident for all protein sources except corn. The regression lines for several protein sources tended to converge at both lower and higher levels of intake . At levels of nitrogen intake below 1 g/m2, protein appeared to be utilized with near 100% efficiency, regardless of source. At levels of intake above 4.4 g/m2 , all nitrogen sources except wheat gluten gave nitrogen balances which did not differ significantly (5% level). In general, caloric intake exerted a positive but diminishing effect on nitrogen balance when nitrogen intake was held constant and caloric intake increased from maintenance to excessive levels. The mean amount of egg nitrogen required to achieve zero nitrogen balance decreased from 3. l g/m2 to 2.2 g/m2 as caloric intake increased from 1475 kilocalories per square meter of body surface area (kcal/m2) to 1760 kcal/m2. The findings are discussed in terms of present energy and protein requirements, the traditional concepts of the biological value of proteins, and the prediction of protein quality from amino acid composition.

Participants demonstrate the Stroop effect when, in naming the color in which a word appears, reaction times are longer when the color and word are incongruent (e.g., "yellow" printed in blue) compared to when they are congruent (e.g., "yellow" printed in yellow). The literature commonly refers to the difference in reaction times as a measure of the interference of word stimuli upon color stimuli, and is taken as support for the theory of automaticity. This study asks whether the Stroop effect can be analyzed as interactions within and across stimulus classes. Adult participants learned three 3-member classes (color, word, and pattern) in a serialized order of training. In the testing phase, participants were presented with compound stimuli formed from combinations of members within and across classes (e.g., word and color), and reaction times were recorded in similar fashion to the Stroop task. Results show that averaged participants' reaction times are faster to compound stimuli comprised of members within the same class, compared to compound stimuli formed with members from different classes. These group-level data are consistent with the Stroop literature in that congruent compounds produce faster reaction times relative to incongruent compounds. However, individual participant data do not consistently reflect the Stroop effect. Further considerations for future research in this area are discussed.