| Summary: | Abnormalities in glucose tolerance such as Type 2 diabetes (T2DM) are associated with cognitive impairment. However, there is an absence of research which investigates whether impaired glucose tolerance (IGT), a precursor of T2DM, is also associated with cognitive impairment. It can be hypothesised that progressively poorer glucose tolerance is associated with a trajectory of increasing cognitive impairment. Low glycaemic index (LGI) and low glycaemic load (LGL) foods are recommended as a method for managing T2DM and IGT. They have also been associated with effects on cognitive function. The potential for LGI and LGL foods to attenuate cognitive impairment associated with abnormalities in glucose tolerance remains unexplored. The main aim of this thesis was to investigate the relationship between glucose tolerance and cognitive performance, across the range of normal glucose tolerance through to seriously impaired glucose tolerance. Study 1, in 23 healthy young adults, demonstrated that the GI of an evening meal can affect objective and subjective cognitive performance the next morning. These findings indicate that an overnight fast is not sufficient to control for the effects of previous nutritional intake, and guided the, design of studies 2 and 3. Study 2 examined cognitive performance and subjective ratings of appetite, mood and alertness in middle-aged females with IGT (n=18) and NGT (n=47) over the morning following the consumption of LGL, HGL, and water breakfasts in a repeated measures design. Study 3 used an identical design to examine cognitive performance in older adults with T2DM (n=24) and age matched non-diabetic adults (n=10). Adults with T2DM showed cognitive impairment on a wide range of cognitive domains, whereas, in those with IGT primarily memory was impaired. Subclinical abnormalities in glucose tolerance can therefore have demonstrable negative effects on cognitive performance, even in ostensibly healthy middle-aged females. As hypothesised, worsening glucose tolerance was associated with a trajectory of cognitive decline. Manipulating the GL of breakfast did not acutely attenuate cognitive impairment in IGT or T2DM. Taken together, these findings suggest that maintaining a state of good health, by preventing the onset of glucose tolerance abnormalities is important for protecting and maintaining cognitive function.
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