The influence of macronutrients on cognitive performance : effects across age and task difficulty : thesis presented in partial fulfillment of the requirements for the degree of Master of Arts in Psychology at Massey University
The effects of pure glucose, protein, and fat ingestion on tasks of paragraph recall, word recall, and mental arithmetic were examined. These effects were also investigated with regard to the age of the participant and the task difficulty level. Twelve young and twelve older adults participated in the study. Over four separate morning sessions, participants ingested one of the four drinks (glucose, protein, fat, or placebo), and completed easy and hard versions of the paragraph recall word recall, and mental arithmetic tasks. The between-group factor was Age of the participant (young or older adult). The within-group factors were type of Nutrient ingested (glucose, protein, fat, or placebo), and Difficulty Level (easy or hard). No effects of Nutrient were found in regard to overall task performance, collapsing across Age and Difficulty Level. There was no effect of Nutrient on the different performance levels of both age groups, or for the two task difficulty levels. However, post-hoc analyses did reveal a significant Nutrient x Age interaction for the elderly after ingestion of the protein drink. Trends in the data also pointed towards an enhancement effect of glucose for the paragraph recall and mental arithmetic tasks. Trends associated with performance levels after fat ingestion showed that fat tended to enhance mental arithmetic accuracy performance for the older adult age group. Protein did not appear to differ from placebo on any of the tasks, with the exception of the deficit in performance seen with the elderly on the mental arithmetic accuracy task. In addition, a post-hoc analysis of the effects of Nutrient on mood-state showed a significant Nutrient x Mood x Time interaction. These results were discussed in light of task-specific effects of nutrients and nutrient metabolism.