Examination of cognitive function during six months of calorie restriction: results of a randomized controlled trial

The effects of time restricted feeding on age-related changes in the mouse retina

Dietary modifications such as caloric restriction (CR) and intermittent fasting (IF) have gained popularity due to their proven health benefits in aged populations. In time restricted feeding (TRF), a form of intermittent fasting, the amount of time for food intake is regulated without restricting the caloric intake. TRF is beneficial for the central nervous system to support brain health in the context of aging. Therefore, we here ask whether TRF also exerts beneficial effects in the aged retina. We compared aged mice (24 months) on a TRF paradigm (access to food for six hours per day) for either 6 or 12 months against young control mice (8 months) and aged control mice on an ad libitum diet. We examined changes in the retina at the functional (electroretinography), structural (histology and fluorescein angiograms) and molecular (gene expression) level. TRF treatment showed amelioration of age-related reductions in both scotopic and photopic b-wave amplitudes suggesting benefits for retinal interneuron signaling. TRF did not affect age-related signs of retinal inflammation or microglial activation at either the molecular or histological level. Our data indicate that TRF helps preserve some aspects of retinal function that are decreased with aging, adding to our understanding of the health benefits that altered feeding patterns may confer.

The impact of continuous calorie restriction and fasting on cognition in adults without eating disorders

Research into the effects of calorie restriction continues to intrigue those interested in whether it may allow humans to live longer and healthier lives. Animal studies of continuous calorie restriction (CCR) and fasting have demonstrated substantial advantages to health and longevity. However, concerns remain about the impact of restricting calorie intake on human health and cognition. Given the emerging evidence of cognitive impairments in eating disorders, studies investigating restricted calorie intake in healthy humans (in an ethical way) may also have implications for understanding restrictive eating disorders. In this review, the published literature on the impact of CCR and fasting on cognitive function in healthy human participants is synthesized. Of the 33 studies of CCR and fasting in humans identified, 23 demonstrated significant changes in cognition. Despite variation across the cognitive domains, results suggest CCR benefits inhibition, processing speed, and working memory, but may lead to impairments in cognitive flexibility. The results of fasting studies suggest fasting is associated with impairments in cognitive flexibility and psychomotor abilities. Overall, the results of these studies suggest the degree (ie, the severity) of calorie restriction is what most likely predicts cognitive improvements as opposed to impairments. For individuals engaging in sustained restriction, this may have serious, irreversible consequences. However, there are mixed findings regarding the impact of CCR and fasting on this aspect of human functioning, suggesting further research is required to understand the costs and benefits of different types of calorie restriction.

Effect of dietary protein intake on cognitive function in the elderly with chronic kidney disease: analysis of the National Health and Nutrition Examination Survey 2011-2014

BACKGROUND

Cognitive dysfunction is prevalent among the elderly diagnosed with chronic kidney disease (CKD). Low protein diets are used for retarding the progression of CKD in clinical practice. Nonetheless, the impact of dietary protein consumption on cognitive function in this population remains uncertain.

METHODS

We recruited 2306 participants (≥60 years) from 2011 to 2014 National Health and Nutrition Examination Survey (NHANES). 24-h dietary recall questionnaire was utilized to evaluate protein intake. Cognitive function was measured using the Consortium to Establish a Registry for Alzheimer's Disease (CERAD), Animal Fluency Test (AFT), and Digit Symbol Substitution Test (DSST). Participants' characteristics were analyzed, and the interaction between protein consumption and CKD on cognitive impairment were analyzed using a logistic regression model.

RESULTS

We divided participants into three groups based on CKD stages: no CKD, CKD stage G1 to G2 (19%), and CKD stage G3 to G5 (18%). The average protein intake was 0.97 g/(kg·d). In the higher protein intake group, CKD stages G1 to G2 elevated the risk of immediate memory impairment (OR: 2.441, 95% Cl: 1.161-5.132 for protein consumption in 1.0-1.2g/(kg·d); OR: 2.225, 95% Cl: 1.015-4.876 for protein consumption in >1.2 g/(kg·d)). However, no similar resuts were observed in the lower protein intake group. In addition, the interaction between CKD status and protein intake on immediate memory was statistically significant (p = .041).

CONCLUSION

A higher probability of cognitive impairment in the elderly with early-stage CKD may be linked to higher protein intake. Low protein diets may be a potential strategy to release cognitive impairment in the elderly with early-stage CKD.

Does dietary nitrate boost the effects of caloric restriction on brain health? Potential physiological mechanisms and implications for future research

Dementia is a highly prevalent and costly disease characterised by deterioration of cognitive and physical capacity due to changes in brain function and structure. Given the absence of effective treatment options for dementia, dietary and other lifestyle approaches have been advocated as potential strategies to reduce the burden of this condition. Maintaining an optimal nutritional status is vital for the preservation of brain function and structure. Several studies have recognised the significant role of nutritional factors to protect and enhance metabolic, cerebrovascular, and neurocognitive functions. Caloric restriction (CR) positively impacts on brain function via a modulation of mitochondrial efficiency, endothelial function, neuro-inflammatory, antioxidant and autophagy responses. Dietary nitrate, which serves as a substrate for the ubiquitous gasotransmitter nitric oxide (NO), has been identified as a promising nutritional intervention that could have an important role in improving vascular and metabolic brain regulation by affecting oxidative metabolism, ROS production, and endothelial and neuronal integrity. Only one study has recently tested the combined effects of both interventions and showed preliminary, positive outcomes cognitive function. This paper explores the potential synergistic effects of a nutritional strategy based on the co-administration of CR and a high-nitrate diet as a potential and more effective (than either intervention alone) strategy to protect brain health and reduce dementia risk.

The Role of Intermittent Fasting and Dieting on Cognition in Adult Population: A Systematic Review of the Randomized Controlled Trials

OBJECTIVE

A healthy diet is a modifiable risk factor that may impact cognition. A unique type of diet may include intermittent fasting (IF), an eating pattern in which individuals go extended periods with little or no meal intake, intervening with periods of normal food intake. IF has multiple health benefits including maintenance of blood glucose levels, reduction of insulin levels, depletion or reduction of glycogen stores, mobilization of fatty acids, and generation of ketones. IF has shown neuroprotective effects as it may lead to increased neurogenesis in the hippocampus, which may contribute to cognitive resilience. Diets including IF were examined as lifestyle modifications in the prevention and management of cognitive decline.

METHODS

A systematic literature search was conducted for randomized controlled trials (RCTs) which assessed the effect of dieting on cognitive functions in adults.

RESULTS

Dietary Approaches to Stop Hypertension (DASH), low-glycemic diets, and caloric restriction have shown improvement in cognitive function; however, there was a negative impact on problem-solving in those with comorbid cardiovascular disease. There is also contradictory evidence that caloric restriction and diet alone may not be sufficient for the improvement of cognitive functions and that exercise may have better efficacy on cognition.

CONCLUSION

IF is considered a safe intervention, and no adverse effects were found in the reviewed studies; however, evidence is limited as there were only 9 low-quality RCTs that assessed the impact of IF on cognition. DASH, low-glycemic diets, and exercise may have effective roles in the management and prevention of cognitive decline, although further research is needed.

Dietary Restriction against Parkinson's Disease: What We Know So Far

Dietary restriction (DR) is defined as a moderate reduction in food intake while avoiding malnutrition. The beneficial effects of DR are being increasingly acknowledged in aging and in a series of age-related neurodegenerative disorders, for example, Parkinson's disease (PD). To date, the pathogenesis of PD remains elusive and there is no cure for it in spite of intensive research over decades. In this review, we summarize the current knowledge on the efficacy of DR on PD, focusing on the underlying mechanisms involving general metabolism, neuroendocrinolgy, neuroinflammation, gut microbiome, and so on. We anticipate that this review will provide future perspectives for PD prevention and treatment.

Life-long dietary restrictions have negligible or damaging effects on late-life cognitive performance: A key role for genetics in outcomes

Several studies report that caloric restriction (CR) or intermittent fasting (IF) can improve cognition, while others report limited or no cognitive benefits. Here, we compare the effects of 20% CR, 40% CR, 1-day IF, and 2-day IF feeding paradigms to ad libitum controls on Y-maze working memory (WM) and contextual fear memory (CFM) in a large population of Diversity Outbred mice that model the genetic diversity of humans. While CR and IF interventions improve lifespan, we observed no enhancement of working memory or CFM in mice on these feeding paradigms, and report 40% CR to be damaging to recall of CFM. Using Quantitative Trait Loci mapping, we identified the gene Slc16a7 to be associated with CFM outcomes in aged mice on lifespan promoting feeding paradigms. Limited utility of dieting and fasting on memory in mice that recapitulate genetic diversity in the human population highlights the need for anti-aging therapeutics that promote cognitive function, with the neuronal monocarboxylate transporter MCT2 encoded by Slc16a7 highlighted as novel target.

Does Neuroinflammation Underlie the Cognitive Changes Observed With Dietary Interventions?

Dietary interventions, such as calorie restriction and ketogenic diet, have been extensively studied in ageing research, including in cognitive decline. Epidemiological studies indicate beneficial effects of certain dietary regimes on mental health, including mood disorders and dementia. However, randomised-controlled trials (the gold-standard of evidence-based medicine) on calorie restriction diets and the ketogenic diet have yet to show clinically convincing effects in neuropsychiatric disorders. This review will examine the quality of studies and evidence base for the ketogenic and calorie restriction diets in common neuropsychiatric conditions, collating findings from preclinical experiments, case reports or small clinical studies, and randomised controlled clinical trials. The major cellular mechanisms that mediate the effects of these dietary interventions on brain health include neuroinflammation, neuroprotection, and neuromodulation. We will discuss the studies that have investigated the roles of these pathways and their interactions. Popularity of the ketogenic and calorie restriction diets has grown both in the public domain and in psychiatry research, allowing for informed review of the efficacy, the limitations, and the side effects of these diets in specific patient populations. In this review we will summarise the clinical evidence for these diets in neuropsychiatry and make suggestions to improve clinical translation of future research studies.

Effects of dietary restriction on cognitive function: a systematic review and meta-analysis

BACKGROUND

Potential positive link between cognitive function and dietary restriction has been widely concerned. The present study describes a systematic review and preliminary meta-analysis to assess the efficacy of dietary restriction on cognitive function. We classified dietary restrictions as Calories Restriction (CR) and Intermittent Fasting (IF).

METHOD

This systematic review and meta-analysis conducted following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Statement (PRISMA) Checklist, Databases including PubMed, Embase, Web of Science, and the Cochrane Library were searched for randomized controlled trials (RCTs) assessing the cognition effectiveness of dietary restriction from database inception to Sep 2021.

RESULT

Eleven RCTs met the inclusion criteria in the systematic review and meta-analysis. The overall effect of dietary restriction on cognitive function is SMD = 0.22 (95% CI: 0.09-0.34, p < 0.01). The effect on global function SMD = 0.35 (95% CI: 0.04-0.65, p < 0.05) and memory SMD = 0.18 (95% CI: 0.00-0.35, p = 0.05) is significant. MCI showed the best effectiveness SMD = 0.36 (95% CI: 0.05-0.68, p < 0.05), followed by the normal weight population SMD = 0.28 (95% CI: 0.03-0.52, p < 0.05) and overweight population SMD = 0.20 (95% CI: 0.06-0.34, p < 0.01). No statistically significant difference showed between IF and CR (p > 0.05).

CONCLUSION

Our study demonstrated that dietary restriction has varying degrees of positive effect on cognitive function in overweight/normal-weight people and MCI. However, it should be cautious when generalizing to other populations. Additional high-quality, large-scale, cohort and intervention studies are needed to further assess the effectiveness of dietary restriction on cognition.

Bridging the Gap: A Geroscience Primer for Neuroscientists With Potential Collaborative Applications

While neurodegenerative diseases can strike at any age, the majority of afflicted individuals are diagnosed at older ages. Due to the important impact of age in disease diagnosis, the field of neuroscience could greatly benefit from the many of the theories and ideas from the biology of aging-now commonly referred as geroscience. As discussed in our complementary perspective on the topic, there is often a "silo-ing" between geroscientists who work on understanding the mechanisms underlying aging and neuroscientists who are studying neurodegenerative diseases. While there have been some strong collaborations between the biology of aging and neuroscientists, there is still great potential for enhanced collaborative effort between the 2 fields. To this end, here, we review the state of the geroscience field, discuss how neuroscience could benefit from thinking from a geroscience perspective, and close with a brief discussion on some of the "missing links" between geroscience and neuroscience and how to remedy them. Notably, we have a corresponding, concurrent review from the neuroscience perspective. Our overall goal is to "bridge the gap" between geroscience and neuroscience such that more efficient, reproducible research with translational potential can be conducted.

Immune Memory in Aging: a Wide Perspective Covering Microbiota, Brain, Metabolism, and Epigenetics

Non-specific innate and antigen-specific adaptive immunological memories are vital evolutionary adaptations that confer long-lasting protection against a wide range of pathogens. Adaptive memory is established by memory T and B lymphocytes following the recognition of an antigen. On the other hand, innate immune memory, also called trained immunity, is imprinted in innate cells such as macrophages and natural killer cells through epigenetic and metabolic reprogramming. However, these mechanisms of memory generation and maintenance are compromised as organisms age. Almost all immune cell types, both mature cells and their progenitors, go through age-related changes concerning numbers and functions. The aging immune system renders the elderly highly susceptible to infections and incapable of mounting a proper immune response upon vaccinations. Besides the increased infectious burden, older individuals also have heightened risks of metabolic and neurodegenerative diseases, which have an immunological component. This review discusses how immune function, particularly the establishment and maintenance of innate and adaptive immunological memory, regulates and is regulated by epigenetics, metabolic processes, gut microbiota, and the central nervous system throughout life, with a focus on old age. We explain in-depth how epigenetics and cellular metabolism impact immune cell function and contribute or resist the aging process. Microbiota is intimately linked with the immune system of the human host, and therefore, plays an important role in immunological memory during both homeostasis and aging. The brain, which is not an immune-isolated organ despite former opinion, interacts with the peripheral immune cells, and the aging of both systems influences the health of each other. With all these in mind, we aimed to present a comprehensive view of the aging immune system and its consequences, especially in terms of immunological memory. The review also details the mechanisms of promising anti-aging interventions and highlights a few, namely, caloric restriction, physical exercise, metformin, and resveratrol, that impact multiple facets of the aging process, including the regulation of innate and adaptive immune memory. We propose that understanding aging as a complex phenomenon, with the immune system at the center role interacting with all the other tissues and systems, would allow for more effective anti-aging strategies.

Eight weeks of intermittent fasting versus calorie restriction does not alter eating behaviors, mood, sleep quality, quality of life and cognitive performance in women with overweight

Human trials that compare intermittent fasting (IF) to calorie restriction (CR) with psychological, behavioral and cognition outcomes are limited. We hypothesized that there would be no difference between CR and IF on perceived eating behaviors, mood, sleep quality, quality of life (QOL) and cognition in women with overweight and obesity. In this prespecified secondary analysis of an open-label, single center, parallel assignment, randomized controlled trial, healthy women with overweight or obesity (N = 46, mean [SD] age 50 [9] years, BMI 32.9 [4.4] kg/m²), without a diagnosed eating disorder and who were randomized into 2 weight loss groups (prescribed 70% of calculated energy requirements as IF or CR) were included. Measurements were assessed in both IF and CR groups following a 12-hour overnight fast during baseline and week 8 and additionally following a 24-hour fast in the IF group only at week 8. We observed that IF produced greater weight and body fat loss than CR (P < .001). We did not detect any statistical difference between groups for the change in dietary restraint, disinhibition, hunger, mood, sleep quality, and QOL. An increase in cognitive performance was found in both IF (P = .036) and CR (P = .006) groups in one of the cognitive tasks, but there was no statistical difference between groups. Perceived eating behaviors, mood, sleep quality and cognitive performance were not changed by an acute 24-hour fast within the IF group (all P > .05). IF may be a viable alternative to CR for weight loss, in the short-term, without adversely impacting eating behaviors, mood, sleep quality, QOL or cognition in healthy women with overweight or obesity. However, larger and long term trials are required.

From famine to therapeutic weight loss: Hunger, psychological responses, and energy balance-related behaviors

Understanding physiological and behavioral responses to energy imbalances is important for the management of overweight/obesity and undernutrition. Changes in body composition and physiological functions associated with energy imbalances provide the structural and functional context in which to consider psychological and behavioral responses. Compensatory changes in physiology and behavior are more pronounced in response to negative than positive energy balances. The physiological and psychological impact of weight loss (WL) occur on a continuum determined by (i) the degree of energy deficit (ED), (ii) its duration, (iii) body composition at the onset of the energy deficit, and (iv) the psychosocial environment in which it occurs. Therapeutic WL and famine/semistarvation both involve prolonged EDs, which are sometimes similar in magnitude. The key differences are that (i) the body mass index (BMI) of most famine victims is lower at the onset of the ED, (ii) therapeutic WL is intentional and (iii) famines are typically longer in duration (partly due to the voluntary nature of therapeutic WL and disengagement with WL interventions). The changes in psychological outcomes, motivation to eat, and energy intake in therapeutic WL are often modest (bearing in mind the nature of the measures used) and can be difficult to detect but are quantitatively significant over time. As WL progresses, these changes become more marked. It appears that extensive WL beyond 10%-20% in lean individuals has profound effects on body composition and physiological function. At this level of WL, there is a marked erosion of psychological functioning, which appears to run in parallel to WL. Psychological resources dwindle and become increasingly focused on alleviating escalating hunger and food seeking behavior. Functional changes in fat-free mass, characterized by catabolism of skeletal muscle and organs may be involved in the drive to eat associated with semistarvation. Higher levels of body fat mass may act as a buffer to protect fat-free mass, functional integrity and limit compensatory changes in energy balance behaviors. The increase in appetite that accompanies therapeutic WL appears to be very different to the intense and all-consuming drive to eat that occurs during prolonged semistarvation. The mechanisms may also differ but are not well understood, and longitudinal comparisons of the relationship between body structure, function, and behavior in response to differing EDs in those with higher and lower BMIs are currently lacking.

Comparison of effects of different dietary interventions on cognitive function in Alzheimer's disease: protocol for systematic review and network meta-analysis

INTRODUCTION

Alzheimer's disease (AD) is the most common neurodegenerative disease and is characterised by cognitive impairment. Non-pharmacological treatments such as diet therapy have been widely investigated in studies on AD. Given the synergistic effects of nutrients present in foods, considering overall dietary composition rather than focusing on a single nutrient may be more useful for evaluating the relationship between diet and AD cognition. The present study aimed to assess the efficacy of different dietary interventions (eg, ketogenic and Mediterranean diets) on cognitive function in patients with AD in a systematic review and pairwise and network meta-analyses of randomised controlled trials or clinical trials.

METHODS AND ANALYSIS

Two reviewers will independently conduct searches of PubMed, Cochrane Central Register of Controlled Trials, Embase, CINAHL, PsycINFO and China National Knowledge Infrastructure databases. Data will be extracted from selected studies and risk of bias will be assessed using the revised Cochrane risk-of-bias tool, and evidence quality will be assessed according to the Grading of Recommendations, Assessment, Development and Evaluation framework. The primary outcome of interest is cognitive function in patients with AD; secondary outcomes include biochemical biomarkers of AD and oxidative stress and/or inflammatory biomarkers in cerebrospinal fluid or plasma. For each outcome, random-effects pairwise and network meta-analyses will be carried out to determine the pooled relative effect of each intervention relative to every other intervention.

ETHICS AND DISSEMINATION

As this study is based solely on published literature, no ethics approval is required. The research will be published in a peer-reviewed journal.

A Conceptual Model of Long-Term Weight Loss Maintenance: The Importance of Cognitive, Empirical and Computational Approaches

Living with obesity is related to numerous negative health outcomes, including various cancers, type II diabetes, and cardiovascular disease. Although much is known about the factors associated with obesity, and a range of weight loss interventions have been established, changing health-related behaviours to positively affect obesity outcomes has proven difficult. In this paper, we first draw together major factors that have emerged within the literature on weight loss to describe a new conceptual framework of long-term weight loss maintenance. Key to this framework is the suggestion that increased positive social support influences a reduction in psychosocial stress, and that this has the effect of promoting better executive functioning which in turn facilitates the development of healthy habits and the breaking of unhealthy habits, leading to improved ongoing maintenance of weight loss. We then outline how the use of computational approaches are an essential next step, to more rigorously test conceptual frameworks, such as the one we propose, and the benefits that a mixture of conceptual, empirical and computational approaches offer to the field of health psychology.

Effects of caloric restriction on human physiological, psychological, and behavioral outcomes: highlights from CALERIE phase 2

Caloric restriction (CR) is a strategy that attenuates aging in multiple nonhuman species. The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) trials are part of a research program aiming to test the effects of CR on aging and longevity biomarkers in humans. Building on CALERIE phase 1, CALERIE phase 2 (CALERIE 2) was the largest study to date to assess sustained CR in healthy humans without obesity. In a 24-month randomized controlled trial comprising 218 participants at baseline, CALERIE 2 showed that moderate CR, 11.9% on average, induced improvements in aging-related biomarkers without adversely affecting psychological or behavioral outcomes. The objectives of this report are to summarize and review the highlights of CALERIE 2 and report previously unpublished results on eating disorder symptoms and cognitive function. This article specifically summarizes the physiological, psychological, aging, behavioral, and safety results of the trial. Also provided are research directions beyond CALERIE 2 that highlight important opportunities to investigate the role of CR in aging, longevity, and health span in humans.

Time-restricted feeding (TRF) for prevention of age-related vascular cognitive impairment and dementia

Aging is the most significant risk factor for vascular cognitive impairment (VCI), and the number of individuals affected by VCI is expected to exponentially increase in the upcoming decades. Yet, there are no current preventative or therapeutic treatments available against the development and progression of VCI. Therefore, there is a pressing need to better understand the pathophysiology underlying these conditions, for the development of novel tools and interventions to improve cerebrovascular health and delay the onset of VCI. There is strong epidemiological and experimental evidence that lifestyle factors, including nutrition and dietary habits, significantly affect cerebrovascular health and thereby influence the pathogenesis of VCI. Here, recent evidence is presented discussing the effects of lifestyle interventions against age-related diseases which in turn, inspired novel research aimed at investigating the possible beneficial effects of dietary interventions for the prevention of cognitive decline in older adults.

Cognitive Impact of Calorie Restriction: A Narrative Review

The impairment of cognitive function can cause substantial emotional and financial burdens. A recent global increasing trend in cognitive impairment and associated disorders has been observed, which will continue to grow as the population ages rapidly. As a nonpharmaceutical approach, calorie restriction (CR) has received extensive research interests due to its health benefits, including maintaining cognitive function. In this narrative review, we first briefly introduce the role of cognitive function in activities of daily living and CR as a part of healthy lifestyle behaviors to protect against cognitive decline. Second, we present results from human studies demonstrating that CR might be beneficial for improving age-related cognitive decline and cognitive impairment in the clinical population such as obesity and type 2 diabetes. Third, the potential mechanisms regarding the protective effects of CR on cognition are discussed. Fourth, specific suggestions are highlighted to be considered in future human studies. Overall, although there are few data available from human studies, CR appears to be beneficial for cognitive protection for both healthy and clinical populations. Further scientific investigations are needed before a firm conclusion can be made.

The effect of caloric restriction on working memory in healthy non-obese adults

OBJECTIVE

We aim to evaluate the effect of caloric restriction (CR) in cognition by comparing performance in neuropsychological tests for working memory between a group of non-obese healthy subjects doing CR for 2 years with another consuming ad libitum diet (AL).

METHODS

This study was part of a larger multicenter trial called CALERIE that consisted of a randomized clinical trial with parallel-group comparing 2 years of 25% CR and AL in 220 volunteers with a BMI between 22 and 28 kg/m2, across 3 sites. The cognitive tests used were the Cambridge Neuropsychological Tests Automated Battery (CANTAB) for Spatial Working Memory (SWM) including the total number of errors (SWMTE) and strategy (SWMS). Included as possible moderators were sleep quality, mood states, perceived stress, and energy expenditure. Analyses were performed at baseline and months 12 and 24.

RESULTS

After adjustments, there was a significantly greater improvement in working memory assessed by the SWM for CR individuals, compared to AL. At month 24, it was related mostly to lower protein intake, compared to other macronutrients. Changes in SWM were moderated by changes in sleep quality, physical activity, and energy expenditure.

CONCLUSION

On the long term, CR in healthy individuals seems to have a slightly positive effect on working memory. The study of brain CR targets opens new possibilities to prevent and treat cognitive deficits.

Pathways of Prevention: A Scoping Review of Dietary and Exercise Interventions for Neurocognition

Alzheimer's disease and related dementias (ADRD) represent an increasingly urgent public health concern, with an increasing number of baby boomers now at risk. Due to a lack of efficacious therapies among symptomatic older adults, an increasing emphasis has been placed on preventive measures that can curb or even prevent ADRD development among middle-aged adults. Lifestyle modification using aerobic exercise and dietary modification represents one of the primary treatment modalities used to mitigate ADRD risk, with an increasing number of trials demonstrating that exercise and dietary change, individually and together, improve neurocognitive performance among middle-aged and older adults. Despite several optimistic findings, examination of treatment changes across lifestyle interventions reveals a variable pattern of improvements, with large individual differences across trials. The present review attempts to synthesize available literature linking lifestyle modification to neurocognitive changes, outline putative mechanisms of treatment improvement, and discuss discrepant trial findings. In addition, previous mechanistic assumptions linking lifestyle to neurocognition are discussed, with a focus on potential solutions to improve our understanding of individual neurocognitive differences in response to lifestyle modification. Specific recommendations include integration of contemporary causal inference approaches for analyzing parallel mechanistic pathways and treatment-exposure interactions. Methodological recommendations include trial multiphase optimization strategy (MOST) design approaches that leverage individual differences for improved treatment outcomes.

Therapeutic strategies for ketosis induction and their potential efficacy for the treatment of acute brain injury and neurodegenerative diseases

The therapeutic use of ketone bodies (KB) against acute brain injury and neurodegenerative disorders has lately been suggested by many studies. Several mechanisms responsible for the protective action of KB have been described, including metabolic, anti-inflammatory and epigenetic. However, it is still not clear whether a specific mechanism of action can be associated with a particular neurological disorder. Different strategies to induce ketosis including the ketogenic diet (KD), caloric restriction (CR), intermittent fasting (IF), as well as the administration of medium chain triglycerides (MCTs), exogenous ketones or KB derivatives, have been used in animal models of brain injury and in humans. They have shown different degrees of success to prevent neuronal damage, motor alterations and cognitive decline. However, more investigation is needed in order to establish safe protocols for clinical application. Throughout the present review, we describe the different approaches that have been used to elevate blood KB and discuss their effectiveness considering their advantages and limitations, as tested in models of brain injury, neurodegeneration and clinical research. We also describe the mechanisms of action of KB in non-pathologic conditions and in association with their protective effect against neuronal damage in acute neurological disorders and neurodegenerative diseases.

Mediterranean and MIND Diets Containing Olive Biophenols Reduces the Prevalence of Alzheimer's Disease

The risk of Alzheimer’s disease (AD) increases with nonmodifiable conditions including age and lack of effective efficacious pharmacotherapy. During the past decades, the non-pharmacotherapy mode of treatment of dietary modification received extensive attention in AD research. In order to reduce the AD pathology and cognitive decline, various dietary patterns have been attempted including caloric restriction (CR), dietary approaches to stop hypertension (DASH), ketogenic diets (KD), Mediterranean diet (MedDi) and Mediterranean-DASH diet Intervention for Neurological Delay (MIND) diet. Higher adherence to the MedDi diet was associated with decreases in cardiovascular and neurological disorders including AD and related cognitive decline. However, another emerging healthy dietary pattern MIND diet has also been associated with slower rates of cognitive decline and significant reduction of AD rate. Olive serves as one of the building block components of MedDi and MIND diets and the exerted potential health beneficial might be suggested due to the presence of its bioactive constituents such as oleic acids and phenolic compounds (biophenols). A few trials using medical food showed an optimal result in presymptomatic or early stages of AD. The review supports the notion that MedDi and MIND diets display potential for maintaining the cognitive function as nonpharmacological agents against AD pathology and proposed preventative mechanism through the presence of olive biophenols and presents the gaps along with the future directions.

Health-Promoting Strategies for the Aging Brain

As the world's population ages and people live longer, the changes in the aging brain present substantial challenges to our health and society. With greater longevity come age-related diseases, many of which have direct and indirect influences on the health of the brain. Although there is some degree of predictable decline in brain functioning with aging, meaningful cognitive decline is not inevitable and is perhaps preventable. In this review, we present the case that the course of aging-related brain disease and dysfunction can be modified. We present the evidence for conditions and risk factors that may contribute to cognitive decline and dementia and for interventions that may mitigate their impact on cognitive functioning later in life, or even prevent them and their cognitive sequelae from developing. Although much work remains to be done to meet the challenges of the aging brain, strategies to promote its health have been demonstrated and offer much promise, which can only be realized if we mount a vigorous public health effort to implement these strategies.

Calorie Intake and Cognitive Function in the Elderly: Data from the Korean Frailty and Aging Cohort Study (KFACS)

This study aimed to clarify the association between calorie intake and cognitive function in community-dwelling older adults. A cross-sectional analysis was performed on the first-year baseline data of 1559 adults aged 70-84 years using population data from the Korean Frailty and Aging Cohort Study. We included 543 participants who participated in nutritional surveys and accurately responded regarding their daily calorie intake. Daily ingestion was measured using the 24-hour dietary recall method, and neuropsychological tests evaluated cognitive characteristics. Logistic regression models were utilized to calculate odds ratios (ORs) with 95% confidence intervals (CIs). The prevalence rate of cognitive impairment was 8%. Subjects with cognitive impairment mainly showed memory loss. After adjusting the confounding factors, participants who had less than the recommended intake were susceptible to cognitive impairment compared to those who that had the proposed intake (adjusted OR: 7.70, 95% CI: 1.01-58.45). We showed that lesser calorie intake than the recommended intake increases the ORs of cognitive impairment. We suggest that an adequate calorie intake protects against cognitive decline, and further studies are essential to investigate the influence of calorie intake reduction on the elderly before widespread application.

Does eating less make you live longer and better? An update on calorie restriction

The complexity of aging is hard to be captured. However, apart from its tissue-specific features, a structural and functional progressive decline of the whole organism that leads to death, often preceded by a phase of chronic morbidity, characterizes the common process of aging. Therefore, the research goal of scientists in the field moved from the search for strategies able to extend longevity to those ensuring healthy aging associated with a longer lifespan referred to as “healthspan”. The aging process is plastic and can be tuned by multiple mechanisms including dietary and genetic interventions. To date, the most robust approach, efficient in warding off the cellular markers of aging, is calorie restriction (CR). Here, after a preliminary presentation of the major debate originated by CR, we concisely overviewed the recent results of CR treatment on humans. We also provided an update on the molecular mechanisms involved by CR and the effects on some of the age-associated cellular markers. We finally reviewed a number of tested CR mimetics and concluded with an evaluation of future applications of such dietary approach.

Nutrition modulation of human aging: The calorie restriction paradigm

Globally, the aging population is growing rapidly, creating an urgent need to attenuate age-related health conditions, including metabolic disease and disability. A promising strategy for healthy aging based on consistently positive results from studies with a variety of species, including non-human primates (NHP), is calorie restriction (CR), or the restriction of energy intake while maintaining intake of essential nutrients. The burgeoning evidence for this approach in humans is reviewed and the major study to date to address this question, CALERIE (Comprehensive Assessment of the Long-term Effects of Reducing Intake of Energy), is described. CALERIE findings indicate the feasibility of CR in non-obese humans, confirm observations in NHP, and are consistent with improvements in disease risk reduction and potential anti-aging effects. Finally, the mechanisms of CR in humans are reviewed which sums up the fact that evolutionarily conserved mechanisms mediate the anti-aging effects of CR. Overall, the prospect for further research in both NHP and humans is highly encouraging.

Calorie restriction in humans: An update

Calorie restriction (CR), a nutritional intervention of reduced energy intake but with adequate nutrition, has been shown to extend healthspan and lifespan in rodent and primate models. Accumulating data from observational and randomized clinical trials indicate that CR in humans results in some of the same metabolic and molecular adaptations that have been shown to improve health and retard the accumulation of molecular damage in animal models of longevity. In particular, moderate CR in humans ameliorates multiple metabolic and hormonal factors that are implicated in the pathogenesis of type 2 diabetes, cardiovascular diseases, and cancer, the leading causes of morbidity, disability and mortality. In this paper, we will discuss the effects of CR in non-obese humans on these physiological parameters. Special emphasis is committed to recent clinical intervention trials that have investigated the feasibility and effects of CR in young and middle-aged men and women on parameters of energy metabolism and metabolic risk factors of age-associated disease in great detail. Additionally, data from individuals who are either naturally exposed to CR or those who are self-practicing this dietary intervention allows us to speculate on longer-term effects of more severe CR in humans.

Persistence of weight loss and acquired behaviors 2 y after stopping a 2-y calorie restriction intervention

Background: Calorie restriction (CR) influences aging processes and extends average and maximal life spans. The CALERIE 2 (Comprehensive Assessment of Long-Term Effects of Reducing Intake of Energy Phase 2) study was the first randomized clinical trial to examine the metabolic and psychological effects of CR in nonobese humans.Objective: We conducted a 2-y follow-up study of adults who underwent 2 y of CR or ad libitum (control) consumption and determined whether weight loss and acquired behaviors persisted after the study ended when participants determined their own lifestyle behaviors.Design: In this prospective, longitudinal study, we assessed differences in weight, body composition, psychological function, and energy expenditure in 39 nonobese [body mass index (in kg/m2): 22-28] men and women (25% CR: n = 24; control: n = 15) 12 and 24 mo after they completed the CALERIE 2 study at Pennington Biomedical.Results: Of 39 participants who were in the follow-up study, 29 subjects (CR: n = 18; control: n = 11) completed all visits at follow-up months 12 and 24. After the CR intervention, a mean ± SEM weight loss of 9.0 ± 0.6 kg was observed in the CR group, in which only 54% of the weight was regained 2 y later. Despite such a regain, weight, the percentage of body fat, and fat mass remained significantly reduced from baseline throughout follow-up and remained significantly less than in the control group (P < 0.05). At follow-up, the CR group retained higher degrees of dietary restraint and avoidance of certain foods.Conclusion: After a 2-y intensive CR intervention, ∼50% of CR-induced weight loss was maintained 2 y later, which was probably the result of lasting effects on acquired behaviors and dietary restraint. This trial was registered at clinicaltrials.gov as NCT00943215.

Executive function in weight loss and weight loss maintenance: a conceptual review and novel neuropsychological model of weight control

Weight loss maintenance is a complex, multifaceted process that presents a significant challenge for most individuals who lose weight. A growing body of literature indicates a strong relationship between cognitive dysfunction and excessive body weight, and suggests that a subset of high-order cognitive processes known as executive functions (EF) likely play an important role in weight management. Recent reviews cover neuropsychological correlates of weight status yet fail to address the role of executive function in the central dilemma of successful weight loss maintenance. In this paper, we provide an overview of the existing literature examining executive functions as they relate to weight status and initial weight loss. Further, we propose a novel conceptual model of the relationships between EF, initial weight loss, and weight loss maintenance, mapping specific executive functions onto strategies known to be associated with both phases of the weight control process. Implications for the development of more efficacious weight loss maintenance interventions are discussed.

Nutritional strategies to optimise cognitive function in the aging brain

Old age is the greatest risk factor for most neurodegenerative diseases. During recent decades there have been major advances in understanding the biology of aging, and the development of nutritional interventions that delay aging including calorie restriction (CR) and intermittent fasting (IF), and chemicals that influence pathways linking nutrition and aging processes. CR influences brain aging in many animal models and recent findings suggest that dietary interventions can influence brain health and dementia in older humans. The role of individual macronutrients in brain aging also has been studied, with conflicting results about the effects of dietary protein and carbohydrates. A new approach known as the Geometric Framework (GF) has been used to unravel the complex interactions between macronutrients (protein, fat, and carbohydrate) and total energy on outcomes such as aging. These studies have shown that low-protein, high-carbohydrate (LPHC) diets are optimal for lifespan in ad libitum fed animals, while total calories have minimal effect once macronutrients are taken into account. One of the primary purposes of this review is to explore the notion that macronutrients may have a more translational potential than CR and IF in humans, and therefore there is a pressing need to use GF to study the impact of diet on brain aging. Furthermore, given the growing recognition of the role of aging biology in dementia, such studies might provide a new approach for dietary interventions for optimizing brain health and preventing dementia in older people.

Dietary Factors and Cognitive Decline

Cognitive decline is an increasingly important public health problem, with more than 100 million adults worldwide projected to develop dementia by 2050. Accordingly, there has been an increased interest in preventive strategies that diminish this risk. It has been recognized that lifestyle factors including dietary patterns, may be important in the prevention of cognitive decline and dementia in later life. Several dietary components have been examined, including antioxidants, fatty acids, and B vitamins. In addition, whole dietary eating plans, including the Mediterranean diet (MeDi), and the Dietary Approaches to Stop Hypertension (DASH) diet, with and without weight loss, have become areas of increasing interest. Although prospective epidemiological studies have observed that antioxidants, fatty acids, and B vitamins are associated with better cognitive functioning, randomized clinical trials have generally failed to confirm the value of any specific dietary component in improving neurocognition. Several randomized trials have examined the impact of changing 'whole' diets on cognitive outcomes. The MeDi and DASH diets offer promising preliminary results, but data are limited and more research in this area is needed.

Aging and brain rejuvenation as systemic events

The effects of aging were traditionally thought to be immutable, particularly evident in the loss of plasticity and cognitive abilities occurring in the aged central nervous system (CNS). However, it is becoming increasingly apparent that extrinsic systemic manipulations such as exercise, caloric restriction, and changing blood composition by heterochronic parabiosis or young plasma administration can partially counteract this age-related loss of plasticity in the aged brain. In this review, we discuss the process of aging and rejuvenation as systemic events. We summarize genetic studies that demonstrate a surprising level of malleability in organismal lifespan, and highlight the potential for systemic manipulations to functionally reverse the effects of aging in the CNS. Based on mounting evidence, we propose that rejuvenating effects of systemic manipulations are mediated, in part, by blood-borne ‘pro-youthful’ factors. Thus, systemic manipulations promoting a younger blood composition provide effective strategies to rejuvenate the aged brain. As a consequence, we can now consider reactivating latent plasticity dormant in the aged CNS as a means to rejuvenate regenerative, synaptic, and cognitive functions late in life, with potential implications even for extending lifespan.

Calorie restriction down-regulates expression of the iron regulatory hormone hepcidin in normal and D-galactose-induced aging mouse brain

It has been shown that iron progressively accumulates in the brain with age. Calorie restriction (CR) may allay many of the adverse effects of aging on the brain, yet the underlying mechanisms, in particular in relation to brain iron metabolism, remain unclear. This study aimed to investigate the role of CR in the regulation of cerebral cellular iron homeostasis. C57BL/6 mice were randomly divided into four groups of eight. The control group was fed a conventional diet ad libitum; the CR group received 70% of the calories of the control mouse intake per day; the D-galactose (D-gal) group received subcutaneous injection of D-gal at a dose of 100 mg/kg once daily to produce mouse model of aging; the D-gal plus CR group received both of the two interventions for 14 weeks. The Morris water maze (MWM) was employed to test the cognitive performance of all animals, and the expression of iron regulatory genes, ferroportin and hepcidin, in the cortex and hippocampus were detected by quantitative real-time PCR. Compared to the controls, the D-gal group mice showed significant spatial reference memory deficits in the MWM test, whereas the D-gal-CR group mice exhibited almost normal cognitive function, indicating that CR protects against D-gal-induced learning and memory impairment. Hepcidin mRNA expression was increased in the D-gal group, decreased in the CR group, and was basically unchanged in the D-gal-CR group. There was no statistical difference in the transmembrane iron exporter ferroportin expression between control and any of the experimental groups. The results suggest that the anti-aging effects of CR might partially lie in its capacity to reduce or avoid age-related iron accumulation in the brain through down-regulating expression of brain hepcidin--the key negative regulator for intracellular iron efflux--and that facilitating the balance of brain iron metabolism may be a promising anti-aging measure.

Similar effects on cognitive performance during high- and low-carbohydrate obesity treatment

OBJECTIVE

Low-carbohydrate (L-CHO) diets are often used for weight loss but their effects on cognitive function are not well understood. The present study compared the effects of a L-CHO and high-carbohydrate (H-CHO) weight-loss diet on cognitive function adults.

DESIGN

PARTICIPANTS were randomized to either a L-CHO (n=22) or H-CHO (n=25) weight-loss diet. Cognitive function was evaluated by four computerized cognitive tasks (Stroop Task, Continuous Performance Task, Word Recall and Wisconsin Card Sorting Task) presented in random order before and at 1, 4, 12 and 24 weeks after the initiation of the L-CHO or H-CHO diet.

PARTICIPANTS

Forty-seven adults (25 males) with a mean±s.d. age of 47.4±8.7 years and body mass index of 35.3±3.4 kg m(-2).

RESULTS

There were no significant differences in weight loss between groups at any time point. There were significant improvements on color Stroop task accuracy over time in both diet groups (P<0.05), but there were no differences in performance between groups on this or any other cognitive task at any time period.

CONCLUSION

These findings suggest that weight loss has neither a positive nor a negative effect on cognitive function and that L-CHO and H-CHO weight-loss diets have similar effects on cognitive performance.

Exercise training plus calorie restriction causes synergistic protection against cognitive decline via up-regulation of BDNF in hippocampus of stroke-prone hypertensive rats

One of the important organ damage of hypertension is cognitive decline. Cognitive function is determined by the function of hippocampus, and previous studies have suggested that the decrease in brain-derived neurotrophic factor (BDNF) in the hippocampus causes cognitive decline. Protection against cognitive decline is reported not only in pharmacological therapy but also in exercise training or calorie restriction. The aim of the present study was to determine whether exercise training plus calorie restriction cause synergistic protection against cognitive decline via BDNF in the hippocampus or not. Exercise training for 28 days improved cognitive decline determined by Morris water maze test via up-regulation of BDNF in the hippocampus of stroke-prone spontaneously hypertensive rats, whereas calorie restriction for 28 days did not. However, exercise training plus calorie restriction causes the protection against cognitive decline to a greater extent than exercise training alone. In conclusion, exercise training plus calorie restriction causes synergistic protection against cognitive decline via up-regulation of BDNF in the hippocampus of stroke-prone hypertensive rats.

Nutrition and neurodegeneration: epidemiological evidence and challenges for future research

The prevention of dementias, such as Alzheimer's disease (AD), is a growing public health concern, due to a lack of effective curative treatment options and a rising global prevalence. Various potential risk or preventive factors have been suggested by epidemiological research, including modifiable lifestyle factors such as diet. Current epidemiological data are in favour of a protective role of certain micronutrients (B vitamins related to homocysteine metabolism, the anti-oxidant vitamins C and E, flavonoids, polyunsatured omega-3 fatty acids, vitamin D) and macronutrients (fish) in the prevention of cognitive decline and dementia/AD. Some factors have been targeted by interventions tested in randomized controlled trials (RCTs), but many of the results are conflicting with observational evidence. Epidemiological analysis of the relations between nutrient consumption and cognitive decline is complex and it is highly unlikely that a single component plays a major role. In addition, since multiple factors across the life course influence brain function in late life, multidomain interventions might be more promising in the prevention of cognitive decline and dementia/AD. Designing such trials remains very challenging for researchers. The main objective of this paper is to review the epidemiologic data linking potential protective factors to cognitive decline or dementia/AD, focusing particularly on the roles of adiposity, caloric restriction, micro (group B vitamins related to homocysteine metabolism, the anti-oxidant vitamins C and E, flavonoids, polyunsatured omega-3 fatty acids, vitamin D) and macronutrients (fish). Limitations of the current data, divergence with results of interventional prevention studies and challenges for future research are discussed.

Caloric restriction augments radiation efficacy in breast cancer

Dietary modification such as caloric restriction (CR) has been shown to decrease tumor initiation and progression. We sought to determine if nutrient restriction could be used as a novel therapeutic intervention to enhance cytotoxic therapies such as radiation (IR) and alter the molecular profile of triple-negative breast cancer (TNBC), which displays a poor prognosis. In two murine models of TNBC, significant tumor regression is noted with IR or diet modification, and a greater regression is observed combining diet modification with IR. Two methods of diet modification were compared, and it was found that a daily 30% reduction in total calories provided more significant tumor regression than alternate day feeding. At the molecular level, tumors treated with CR and IR showed less proliferation and more apoptosis. cDNA array analysis demonstrated the IGF-1R pathway plays a key role in achieving this physiologic response, and multiple members of the IGF-1R pathway including IGF-1R, IRS, PIK3ca and mTOR were found to be downregulated. The innovative use of CR as a novel therapeutic option has the potential to change the biology of tumors and enhance the opportunity for clinical benefit in the treatment of patients with TNBC.

Intentional weight loss in overweight and obese individuals and cognitive function: a systematic review and meta-analysis

High adiposity in middle age is associated with higher dementia risk. The association between weight loss and cognitive function in older adults is still controversial. A meta-analysis was undertaken to estimate the effectiveness of intentional weight loss on cognitive function in overweight and obese adults. A structured strategy was used to search randomized and non-randomized studies reporting the effect of intentional and significant weight loss on cognitive function in overweight and obese subjects. Information on study design, age, nutritional status, weight-loss strategy, weight lost and cognitive testing was extracted. A random-effect meta-analysis was conducted to obtain summary effect estimates for memory and attention-executive domains. Twelve studies met inclusion criteria. Seven were randomized trials and the remaining five included a control group. A low-order significant effect was found for an improvement in cognitive performance with weight loss in memory (effect size 0.13, 95% CI 0.00-0.26, P=0.04) and attention/executive functioning (effect size 0.14, 95% CI 0.01-0.27, P<0.001). Studies were heterogeneous in study design, sample selection, weight-loss intervention and assessment of cognitive function. Weight loss appears to be associated with low-order improvements in executive/attention functioning and memory in obese but not in overweight individuals.

Caloric restriction in humans: impact on physiological, psychological, and behavioral outcomes

The current societal environment is marked by overabundant accessibility of food coupled with a strong trend of reduced physical activity, both leading to the development of a constellation of disorders, including central obesity, insulin resistance, dyslipidemia, and hypertension (metabolic syndrome). Prolonged calorie restriction (CR) has been shown to extend both the median and maximal lifespan in a variety of lower species such as yeast, worms, fish, rats, and mice. Mechanisms of this CR-mediated lifespan extension are not fully elucidated, but possibly involve significant alterations in energy metabolism, oxidative damage, insulin sensitivity, inflammation, and functional changes in both the neuroendocrine and sympathetic nervous systems. Here we review some of the major physiological, psychological, and behavioral changes after 6 months of CR in overweight otherwise healthy volunteers. Special emphasis is given to the first completed clinical studies that have investigated the effects of controlled, high-quality energy-restricted diets on both biomarkers of longevity and on the development of chronic diseases related to age in humans. With the incremental expansion of research endeavors in the area of energy or caloric restriction, data on the effects of CR in animal models and human subjects are becoming more accessible.

Neuronal and cognitive plasticity: a neurocognitive framework for ameliorating cognitive aging

What is the neurocognitive basis for the considerable individual differences observed in functioning of the adult mind and brain late in life? We review the evidence that in healthy old age the brain remains capable of both neuronal and cognitive plasticity, including in response to environmental and experiential factors. Neuronal plasticity (e.g., neurogenesis, synaptogenesis, cortical re-organization) refers to neuron-level changes that can be stimulated by experience. Cognitive plasticity (e.g., increased dependence on executive function) refers to adaptive changes in patterns of cognition related to brain activity. We hypothesize that successful cognitive aging requires interactions between these two forms of plasticity. Mechanisms of neural plasticity underpin cognitive plasticity and in turn, neural plasticity is stimulated by cognitive plasticity. We examine support for this hypothesis by considering evidence that neural plasticity is stimulated by learning and novelty and enhanced by both dietary manipulations (low-fat, dietary restriction) and aerobic exercise. We also examine evidence that cognitive plasticity is affected by education and training. This is a testable hypothesis which could be assessed in humans in randomized trials comparing separate and combined effects of cognitive training, exercise, and diet on measures of cognitive and brain integrity. Greater understanding of the factors influencing the course of cognitive aging and of the mechanisms underlying those factors could provide information on which people could base choices that improve their ability to age successfully.