The impact of diet-based glycaemic response and glucose regulation on cognition: evidence across the lifespan

The brain has a high metabolic rate and its metabolism is almost entirely restricted to oxidative utilisation of glucose. These factors emphasise the extreme dependence of neural tissue on a stable and adequate supply of glucose. Whereas initially it was thought that only glucose deprivation (i.e. under hypoglycaemic conditions) can affect brain function, it has become apparent that low-level fluctuations in central availability can affect neural and consequently, cognitive performance. In the present paper the impact of diet-based glycaemic response and glucose regulation on cognitive processes across the lifespan will be reviewed. The data suggest that although an acute rise in blood glucose levels has some short-term improvements of cognitive function, a more stable blood glucose profile, which avoids greater peaks and troughs in circulating glucose is associated with better cognitive function and a lower risk of cognitive impairments in the longer term. Therefore, a habitual diet that secures optimal glucose delivery to the brain in the fed and fasting states should be most advantageous for the maintenance of cognitive function. Although the evidence to date is promising, it is insufficient to allow firm and evidence-based nutritional recommendations. The rise in obesity, diabetes and metabolic syndrome in recent years highlights the need for targeted dietary and lifestyle strategies to promote healthy lifestyle and brain function across the lifespan and for future generations. Consequently, there is an urgent need for hypothesis-driven, randomised controlled trials that evaluate the role of different glycaemic manipulations on cognition

A temporary deficiency in self-control:can heightened motivation overcome this effect?

Self-control is important for everyday life and involves behavioral regulation. Self-control requires effort, and when completing two successive self-control tasks, there is typically a temporary drop in performance in the second task. High self-reported motivation and being made self-aware somewhat counteract this effect-with the result that performance in the second task is enhanced. The current study explored the relationship between self-awareness and motivation on sequential self-control task performance. Before employing self-control in an antisaccade task, participants initially applied self-control in an incongruent Stroop task or completed a control task. After the Stroop task, participants unscrambled sentences that primed self-awareness (each started with the word "I") or unscrambled neutral sentences. Motivation was measured after the antisaccade task. Findings revealed that, after exerting self-control in the incongruent Stroop task, motivation predicted erroneous responses in the antisaccade task for those that unscrambled neutral sentences, and high motivation led to fewer errors. Those primed with self-awareness were somewhat more motivated overall, but motivation did not significantly predict antisaccade performance. Supporting the resource allocation account, if one was motivated-intrinsically or via the manipulation of self-awareness-resources were allocated to both tasks leading to the successful completion of two sequential self-control tasks

Glucose effects on long-term memory performance : duration and domain specificity.

Rational; Previous research has suggested that long term- verbal declarative memory is particularly sensitive to enhancement by glucose loading, however investigation of glucose effects on certain memory domains has hitherto been neglected. Therefore domain specificity of glucose effects merits further elucidation. Objectives; The aim of the present research was to provide a more comprehensive investigation of the possible effects of glucose administration on different aspects of memory by i) contrasting the effect of glucose administration on different memory domains (implicit/ explicit memory; verbal/ non-verbal memory, recognition/ familiarity processes), ii) investigating whether potential effects on memory domains differ depending on the dose of glucose administered (25g versus 60g), iii) exploring the duration of the glucose facilitation effect (assessment of memory performance 35 min and 1 week after encoding). Methods; a double blind, between- subjects design was used to test the effects of administration of 25 and 60g glucose on memory performance. Results; Implicit memory was improved following administration of 60g of glucose. Glucose supplementation failed to improve face recognition performance but significantly improved performance of word recall and recognition following administration of 60g of glucose. However, effects were not maintained one-week following encoding. Conclusions; Improved implicit memory performance following glucose administration has not been reported before. Furthermore the current data tentatively suggest that level of processing may determine the required glucose dosage to demonstrate memory improvement and that higher dosages may be able to exert effects on memory pertaining to both hippocampal and non-hippocampal brain regions

Metabolic Agents that Enhance ATP can Improve Cognitive Functioning: A Review of the Evidence for Glucose, Oxygen, Pyruvate, Creatine, and L-Carnitine

Over the past four or five decades, there has been increasing interest in the neurochemical regulation of cognition. This field received considerable attention in the 1980s, with the identification of possible cognition enhancing agents or “smart drugs”. Even though many of the optimistic claims for some agents have proven premature, evidence suggests that several metabolic agents may prove to be effective in improving and preserving cognitive performance and may lead to better cognitive aging through the lifespan. Aging is characterized by a progressive deterioration in physiological functions and metabolic processes. There are a number of agents with the potential to improve metabolic activity. Research is now beginning to identify these various agents and delineate their potential usefulness for improving cognition in health and disease. This review provides a brief overview of the metabolic agents glucose, oxygen, pyruvate, creatine, and L-carnitine and their beneficial effects on cognitive function. These agents are directly responsible for generating ATP (adenosine triphosphate) the main cellular currency of energy. The brain is the most metabolically active organ in the body and as such is particularly vulnerable to disruption of energy resources. Therefore interventions that sustain adenosine triphosphate (ATP) levels may have importance for improving neuronal dysfunction and loss. Moreover, recently, it has been observed that environmental conditions and diet can affect transgenerational gene expression via epigenetic mechanisms. Metabolic agents might play a role in regulation of nutritional epigenetic effects. In summary, the reviewed metabolic agents represent a promising strategy for improving cognitive function and possibly slowing or preventing cognitive decline

Hormone replacement therapy is associated with improved verbal declarative memory in healthy relatively recent postmenopausal women.

The efficacy of Hormone Replacement Therapy (HRT) for cognitive health in postmenopausal women has been systematically questioned during the last decade. Although epidemiological and clinical research have suggested that HRT may exert protective effects on the prophylaxis of neurodegenerative diseases and beneficial effects on cognitive function, the Women's Health Initiative Memory Study (WHIMS) contradicted these claims. The purpose of this study was to reassess the effects of HRT on cognitive function in an attempt to account for two potential confounding factors that might have generated the negative clinical findings reported by the WHIMS i.e. subjects' age and educational level

Breakfast, Glycemic Index, and Cognitive Function in School Children:Evidence, Methods, and Mechanisms

Breakfast has been claimed to improve cognitive function and academic performance, leading to the provision of breakfast initiatives by public health bodies. Children may be particularly sensitive to the nutritional effects of breakfast due to greater energetic needs compared to adults. However, there is a lack of acute intervention studies assessing what type of breakfast is optimal for cognitive performance. In this paper, the impact of breakfast-based glycemic response on cognition in children will be reviewed. The data suggest that a more stable blood glucose profile which avoids greater peaks and troughs in circulating glucose levels is associated with better cognitive function across the morning. Although the evidence to date is promising, it is currently insufficient to allow firm and evidence-based recommendations. What limits our ability to draw conclusions from previous findings is that the studies have differed widely with respect to subject characteristics, cognitive tests used, and timing of cognitive assessment. In addition, few studies have profiled glycemic response in children specifically. There is, therefore, an urgent need for hypothesis-driven, randomized, controlled trials that evaluate the role of different glycemic manipulations on cognition

Can administration of glucose facilitate memory processes?

The brain has a very high rate of energy consumption relative to its size, and requires a ready supply of ‘fuel’. Glucose is the major fuel for the brain, and the continuous delivery of glucose via the bloodstream is essential for the normal functioning of the central nervous system. The relationship between normal brain functioning and glucose has been well established for many years. However, it was not until relatively recently that systematic investigations into the cognitive effects of variations in blood glucose levels were begun. Over the past decade, it has been clearly demonstrated that changes in blood glucose levels can affect memory processes. We here present some of our studies that have investigated whether the administration of glucose (and its primary biochemical reagent—oxygen) can significantly facilitate memory processes in healthy, young individuals. The implications of our findings for the cognitive neuroscience of memory will also be considered

Changes in emotional state and cognition following administration of low-, medium- and high-energy foodstuff : the effect of dieting and dietary restraint.

The aim of this study was to investigate changes in emotional state, food perception and cognition following administration of small quantities of low-, medium- or high-energy food. Thirty-eight female dieters and non-dieters aged 18–51 years (mean BMI=24.6 kg m−2) were asked to rate their emotional state before and after consumption and dietary restraint was determined using the Three-Factor Eating Questionnaire (Stunkard & Messick, 1985). The results showed that participants felt fuller and more energetic as energy content increased, whereas perception of “healthiness” and “safeness” of food decreased. Higher levels of anxiety were observed after ingestion of the medium-energy than after the low-energy food. Irrespective of the energy content, restrained eaters felt significantly more energetic than non-restrained eaters, whereas dieters reported significantly lower positive mood ratings than non-dieters following food administration. Although no significant effect of dietary restraint, dieting or energy content was observed on working memory, dieters’ performance was lower after consumption of a high-energy food. In conclusion, the study provided further evidence that energy content and psychological features of foods can alter emotional state and it can be tentatively suggested from these data that psychologically mediated changes in emotional responses to food and, more specifically, participants’ dieting behaviour should be taken into account when assessing the effects of nutrition on mood and cognition