The Effects of High and Low GI Breakfasts on Cognitive Performance in Adults With Type 2 Diabetes

Consumption of a low glycemic index (GI) diet has been shown to improve glycaemic control in type 2 diabetics(Brand-Miller et al., 2003; Jenkins et al., 2008). In addition to the benefits for glycaemic control there is some evidence for acute improvements in cognitive performance after consumption of low GI foods compared with high GI foods in both adults (Benton et al., 2003; Kaplan et al., 2000) and adolescents (Ingwersen et al., 2007; Smith and Foster, 2008).

Given these findings it is possible that low GI focused dietary interventions designed to improve glycaemic control and health outcomes for diabetic patients could also improve the cognitive function of these patients. This is of particular relevance in light of the evidence associating type 2 diabetes with cognitive decrements (Awad et al., 2004; Stewart and Loilitsa 1999; van Harten et al., 2006). To date two studies with type 2 diabetics have reported that a low GI breakfast was associated with increased verbal memory performance compared to a high GI breakfast (Greenwood et al., 2003; Papanikolaou et al. 2006). Further research should investigate the benefit of low GI foods to cognition.

The aim of this study is to examine the effects of high and low glycaemic index breakfast on cognitive performance in adults with type 2 diabetes. Participants will perform a battery of cognitive tests after consuming 3 different breakfasts (high GI, low GI, and water) on 3 different tests days. The participants will be recruited from the general public and from the Leeds Teaching Hospital diabetes clinic.

This research can benefit the development of specific dietary behaviours aimed at reducing diabetes related cognitive decline. This research is part of a PhD funded by the Economic and Social Research Council and the University of Leeds.

The study will conform to a randomised mixed design. Both the diabetic experimental group and the control group will take part in three conditions whereby participants will receive a high GI, a low GI, or a water breakfast delivered in a counterbalanced order. Participants will then perform the battery of cognitive tests on 2 occasions throughout the morning; 30 minutes after breakfast and 180 minutes after breakfast. Blood glucose will be measured from capillary finger-prick blood samples using diabetic glucose meters throughout the morning.

Eligibility Criteria:
Inclusion Criteria:

* Able to give informed consent
* Type 2 diabetes
* White British or White North American ethnicity and native English speakers
* Not previously received or currently received subcutaneous insulin as part of their diabetes treatment.
* Vision sufficiently good to complete the cognitive testing (using glasses and/or lenses).

Exclusion Criteria:

* Dementia (as indicated using the Mini Mental State Examination \<26)
* Current (or recent i.e. in last 6 months) cigarette smoker
* Neurological disorder
* Previous stroke
* Medication other than diabetes treatment medication that has a direct effect on the brain and is likely to influence cognitive function.

Co-existent diabetic complications will not be considered exclusion criteria unless they result in inability to complete the cognitive testing (e.g. insufficient vision).

These exclusion criteria have been chosen on the basis that these are factors that can affect cognitive performance. Given that the cognitive tests involve learning English words, only participants who have English as their first language can be included because different cognitive processes are used when learning in a non-native language (Wong et al., 2004). Ethnicity can influence glucose regulation and risk of diabetes. Given that part of this research is examining the relationship between glucose regulation and cognition it is important that potential confounds such as ethnicity/genetic propensity to diabetes are controlled for.