Discussion
cognitive and executive functions, cognitive impairment, noninsulin-dependent T2DM, prediabetes, cognitive or mood effects of the meal profiles, sleepiness, cognitive and mood benefits, satiety, T2DM
EFFECTS LATE, PREDIABETES, OTHER METABOLIC DISORDERS
The aim of this study was to explore the cognitive effects of a multimeal paradigm that produced an LGI response over the course of the day relative to meals which produced an HGI response in patients with noninsulin-dependent T2DM. Overall, there were no cognitive effects for 7 of the 9 cognitive performance measures. However, there were modest cognitive benefits in the period before lunch (2.5–3 h after breakfast), as demonstrated by better global cognitive function for the LGIP relative to the HGIP and specifically, better accuracy for the RVIP task, a measure of executive function. As a combination of all the cognitive tests, the global outcome offers insight into the general direction of effects across the board. Therefore, these results indicate that there is some acute cognitive benefit for patients with T2DM when following meal patterns that are associated with a steadier glycemic response, such as lower peaks and a tapered decline over the postprandial period. This is one of the first studies to assess cognition in patients with T2DM utilizing a multimeal paradigm. The present findings are consistent with studies showing an LGI breakfast is associated with cognitive benefits in prediabetes and T2DM relative to an HGI breakfast [Interestingly, the period before lunch when cognitive benefits were observed did not coincide with glycemic differences between the conditions. Indeed, this asynchrony between cognitive and glycemic effects has been observed previously in healthy young adults [Differences in mood state may also have played a role in the cognitive effects in the morning. For example, the interactions indicated that hunger and sleepiness were higher for the HGIP prior to lunch; however, the pairwise comparisons were NS. This is partially consistent with evidence that lower GI meals are associated with reduced feelings of hunger and increased satiety relative to high GI meals [It was evident in the present study that there were no cognitive or mood effects of the meal profiles in the afternoon, either during the postprandial response to lunch or following an afternoon snack. The simplest conclusion is that there are limited effects of glycemic response and associated physiological processes on cognition during this phase of the day. It is possible that the systematic application of type 1 error correction using the Bonferroni method to the analysis models could lead to type 2 error. It is also possible that our study was underpowered, given that the power calculation was based on a cognitive performance measure that was not assessed in this study. Variation in cognitive measures between studies in this field significantly limits the ability to use the exact same task when calculating a-priori effect size. The absence of other studies exploring the late afternoon phase following glycemic nutritional interventions means further work is required. However, null effects in the GI cognitive field are not unusual in studies with healthy adults [There are a number of limitations to this research. The absence of blood samples renders mechanistic explanations relating to insulin, FFAs, or other plasma characteristics speculative. It would be useful to compare the cognitive performance and glycemic responses of the T2DM sample to a healthy age-matched control group. This would serve 2 purposes; it would enable characterization of the degree of cognitive impairment in this T2DM sample, and it would indicate the relative effectiveness of the LGIP for producing a glycemic response akin to a healthy adult. Nutritional effects on cognitive function are most likely in those with greater capacity for improvement, such as those with more severe T2DM, or in cases where the intervention is particularly effective at benefiting a physiological response, in this case, the glycemic response. Assessing these parameters is not directly possible without a healthy control group. It is noteworthy, though, that the glycemic response to the breakfasts did not differ in the period up to lunch. This indicates that the initial breakfast meal was not effective in producing a differential response between the 2 conditions, which could explain the absence of effects later in the day, that is, a null second meal cognitive effect. Perhaps the breakfast meal is critical for determining cognitive function throughout the remainder of the day. Future studies with a multimeal paradigm would benefit from the inclusion of a breakfast that produces a clear physiological difference between the comparator conditions. Previous research also shows that nutritional interventions in T2DM are most effective when the cognitive demand is high, and the task is verbal memory based [In summary, this study shows that a multimeal paradigm using low GI foods over breakfast, lunch, and an afternoon snack broadly producing a lower glycemic response is associated with modest benefits for cognitive function in patients with noninsulin-dependent T2DM, relative to a meal profile with HGI foods producing a higher glycemic response. For most cognitive outcomes and measures of mood and satiety, there were no differences between the conditions. Interestingly, the benefits for global cognitive and executive functions were only observed ∼2.5–3 h after breakfast, immediately prior to lunch, at a point when the glycemic response was not different between the 2 conditions. Further research is required to explore possible mechanisms and explore the utility of a longer multimeal paradigm for cognitive and mood benefits in patients with T2DM and other metabolic disorders.