Preliminary evidence that glucose ingestion facilitates prospective memory performance

The Impact of Free and Added Sugars on Cognitive Function: A Systematic Review and Meta-Analysis

A relationship between excessive sugar consumption and cognitive function has been described in animal models, but the specific effects of sugars in humans remains unclear. This systematic review and meta-analysis aimed to evaluate the current knowledge, research characteristics, and quality of evidence of studies investigating the impacts of free and added sugars on human cognition in healthy participants. The review identified 77 studies (65 experimental trials, n = 3831; 9 cross-sectional studies, n = 11,456; and 3 cohort studies, n = 2059). All cohort studies and eight of the nine cross-sectional studies found significant positive correlations between added sugar consumption and risk of cognitive impairment. Four studies identified reduced risk of cognitive impairment associated with natural fructose-containing foods. The majority of randomised control trials assessed short-term glucose facilitation effects on cognitive outcomes. The results from these studies suggest the need for a tightly regulated blood glucose level, dependent on individualised physiological factors, for optimal cognitive function. A meta-analysis of a subset of studies that assessed the impact of glucose on recall found improvements in immediate free recall compared to controls (p = 0.002). The findings highlight the potentially detrimental effect of excessive, long-term, or prenatal added sugar consumption on cognitive function. Further research is needed to examine the specific effects of free and added sugars on cognitive function.

A Study on Legume-Based Noodles as Staple Food for Office Workers

This study aims to verify the effects of “legume-based noodles” as a staple food for lunch, specifically: blood glucose, cognitive function tests, Kansei value, work questionnaires, typing, and body weight. The experiment is divided into two groups: the intervention group (legumes-based noodle) and the control group (regular lunch). Both groups have similar menu except the staple food. The intervention group resulted in a statistically significant lower blood glucose area under the curve (AUC) and lower maximum blood glucose levels during the afternoon work hours on weekdays. In addition, the Kansei value “concentration” decreased at the end of the workday in the control group compared to before and after lunch but did not decrease in the intervention group. Furthermore, the number of typing accuracy was higher in the intervention group than in the control group, and the questionnaire responses for “work efficiency” and “motivation” were more positive. These results suggest that eating legume-based noodles may lead to improved performance of office workers.

Effect of glucose and sucrose on cognition in healthy humans: a systematic review and meta-analysis of interventional studies

CONTEXT

Evidence suggests that plasma glucose levels may influence cognitive performance, but this has not been systematically reviewed and quantified.

OBJECTIVE

The aim of this review was to investigate the potential effects of glucose and sucrose, compared with placebo, on cognition in healthy humans.

DATA SOURCES

The electronic databases PubMed and Web of Science were searched up to December 2019. Reference lists of selected articles were checked manually.

STUDY SELECTION

Randomized controlled trials or crossover trials that compared glucose or sucrose with placebo for effects on cognition were eligible.

DATA EXTRACTION

Potentially eligible articles were selected independently by 2 authors. Risk of bias was assessed through the Cochrane Collaboration tool. Standardized mean differences (SMDs) were obtained from random-effects meta-analyses for a subsample of studies that reported the same outcomes.

RESULTS

Thirty-seven trials were identified, of which 35 investigated the effect of glucose consumption compared with placebo on cognition. Two studies found no effect of glucose on cognition, while the others found mixed results. Only 3 of the 37 studies investigated the effects of sucrose intake, reporting mixed results. Meta-analyses revealed a significantly positive effect of glucose compared with control, but only when a verbal performance test (immediate word recall) was used in parallel-design studies (SMD = 0.61; 95%CI, 0.20-1.02; I2 = 0%). Twenty-four studies were classified as having high risk of bias for the selection procedure.

CONCLUSIONS

A limited body of evidence shows a beneficial effect of glucose in individuals performing immediate verbal tasks. High-quality trials with standardized cognitive measurements are needed to better establish the effect of glucose or sucrose on cognition.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42019122939.

Mental energy: plausible neurological mechanisms and emerging research on the effects of natural dietary compounds

Objective: Lack of mental energy is one of the leading reasons adults turn to dietary supplements, with three out of ten supplement users hoping to improve their energy level; even more consume caffeine-containing products for the same reason. Despite this interest from consumers, there is no consensus scientific definition of mental energy or sole validated instrument for measuring it. We performed this review to summarize main findings from research regarding the influence of natural dietary compounds on three aspects of mental energy: cognition (vigilance), motivation (to do mental work), and mood (feelings of energy and/or absence of feelings of fatigue).Methods: A narrative review of key papers.Results: In addition to caffeine, a number of other compounds, including the polyphenols, which are found in all plant-derived products, and the phytochemicals in culinary herbs and herbal products such as Panax ginseng and Ginkgo biloba, have been shown in animal models to modulate neurotransmitter activity potentially relevant to mental energy. Inadequate intake of B vitamins could also potentially have a negative effect on mental energy due to their role in overall energy production, as precursors of key cofactors in the citric acid cycle, as well as their role in brain function and neurotransmitter synthesis. Consumption of some of these products may have direct or indirect effects on one or more elements of mental energy.Conclusion: Large, prospective clinical trials of these products using appropriate, validated instruments designed to measure mental energy may be worthwhile if sufficient evidence exists to justify such trials.

The Effects of Carbohydrates, in Isolation and Combined with Caffeine, on Cognitive Performance and Mood-Current Evidence and Future Directions

This review examines the effects of carbohydrates, delivered individually and in combination with caffeine, on a range of cognitive domains and subjective mood. There is evidence for beneficial effects of glucose at a dose of 25 g on episodic memory, but exploration of dose effects has not been systematic and the effects on other cognitive domains is not known. Factors contributing to the differential sensitivity to glucose facilitation include age, task difficulty/demand, task domain, and glucoregulatory control. There is modest evidence to suggest modulating glycemic response may impact cognitive function. The evidence presented in this review identifies dose ranges of glucose and caffeine which improve cognition, but fails to find convincing consistent synergistic effects of combining caffeine and glucose. Whilst combining glucose and caffeine has been shown to facilitate cognitive performance and mood compared to placebo or glucose alone, the relative contribution of caffeine and glucose to the observed effects is difficult to ascertain, due to the paucity of studies that have appropriately compared the effects of these ingredients combined and in isolation. This review identifies a number of methodological challenges which need to be considered in the design of future hypothesis driven research in this area.

Glucose Content and In Vitro Bioaccessibility in Sweet Potato and Winter Squash Varieties during Storage

Glucose content and in vitro bioaccessibility were determined in raw and cooked pulp of Arapey, Cuabé, and Beauregard sweet potato varieties, as well as Maravilla del Mercado and Atlas winter squash, after zero, two, four, and six months of storage (14 °C, 80% relative humidity (RH)). The total glucose content in 100 g of raw pulp was, for Arapey, 17.7 g; Beauregard, 13.2 g; Cuabé, 12.6 g; Atlas, 4.0 g; and in Maravilla del Mercado, 4.1 g. These contents were reduced by cooking process and storage time, 1.1 to 1.5 times, respectively, depending on the sweet potato variety. In winter squash varieties, the total glucose content was not modified by cooking, while the storage increased glucose content 2.8 times in the second month. After in vitro digestion, the glucose content released was 7.0 times higher in sweet potato (6.4 g) than in winter squash (0.91 g) varieties. Glucose released by in vitro digestion for sweet potato stored for six months did not change, but in winter squashes, stored Atlas released glucose content increased 1.6 times. In conclusion, in sweet potato and winter squash, the glucose content and the released glucose during digestive simulation depends on the variety and the storage time. These factors strongly affect the supply of glucose for human nutrition and should be taken into account for adjusting a diet according to consumer needs.

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.

Body mass loss correlates with cognitive performance in primates under acute caloric restriction conditions

Brain functions are known to consume high levels of energy, thus, the integrity of cognitive performance can be drastically impacted by acute caloric restriction. In this study, we tested the impact of a 40% caloric restriction on the cognitive abilities of the grey mouse lemur (Microcebus murinus). Twenty-three male mouse lemurs were divided into two groups: 13 control animals (CTL) that were fed with 105kJ/day and 10calorie restricted (CR) animals that received 40% less food (63kJ/day) than the CTL animals. The animals were fed according to their group for 19days. Before treatment, we assessed baseline associative learning capacities, resting metabolic rates and locomotor performance of both animal groups. After treatment, we tested the same functions as well as long-term memory. Our results showed that CR animals had lower learning performance following caloric restriction. The effects of caloric restriction on memory recall varied and depended on the metabolism of the individual animal. Body mass loss was linked to memory test performance in the CR group, and lower performance was observed in individuals losing the most weight. While CR was observed to negatively impact learning, locomotor capacities were preserved in CR animals, and there were higher resting metabolic rates in the CR group. Our data reinforce the strong link between energy allocation and brain function, and suggest that in the context of food shortage, learning capacities could be a limiting parameter in the adaptation to a changing environment.

Glucose enhancement of event-related potentials associated with episodic memory and attention

Previous studies have reported that increasing glycaemia by a glucose-containing drink enhances memory functioning. The aim of the present study was to extend this literature by examining the effects of glucose on episodic memory as well as attention processes, and to investigate associated event-related potential (ERP) markers. Fifteen minutes after treatment (25 g glucose or placebo drink), 35 participants performed an old/new recognition memory task and a Stroop colour naming task. Consistent with previous research, when controlling for glucose regulation, cognitive facilitation was observed behaviourally for verbal memory, but there was also a trend towards attentional facilitation. Furthermore, across both domains, it was the most demanding task conditions that exhibited glucose sensitivity. In support of the behavioural results, the analysis of ERPs across treatment groups revealed an enhanced left-parietal old/new effect related to recollection, and also suggested modulation of attentional processes. The results suggest that glucose may facilitate attention as well as memory.

Glucose and memory: the influence of drink, expectancy, and beliefs

RATIONALE

An increasing number of studies suggest that glucose can enhance aspects of memory and the central methodology is the use of the glucose-placebo design. One critical issue therefore is separating the pharmacological effects of glucose from the expectancies created by consuming a drink that might contain glucose.

OBJECTIVE

A modified balanced placebo design examined the role that expectancy and belief about the drink consumed has on the pharmacological changes observed following glucose consumption.

METHOD

Ninety-three participants, allocated according to a drink (glucose, placebo) × message (told glucose, told nothing, told placebo) unrelated design, were administered tasks assessing immediate and delayed verbal free recall, spatial recognition and semantic verification. Each task has some evidence for hippocampus involvement, and variations in task difficulty were used to assess the idea that glucose effects are sensitive to task difficulty.

RESULTS

While the messages biased drink judgements in the expected direction, judgements of drink content were at chance and glucose only enhanced delayed free recall. The subtle effects of the messages did not modify the glucose enhancement. However, believing glucose had been consumed showed an independent improvement in delayed free recall. There was no evidence that task complexity enhanced the glucose effect.

CONCLUSIONS

The findings indicate that expectancy effects are unlikely to be confused with glucose enhancements, but beliefs about consuming glucose can augment performance on delayed free recall. The discussion considers the hippocampus and complexity hypotheses of glucose's mode of action and proposes the routine collection of drink beliefs in future studies.