Microbiota Gut-Brain Axis (MGBA)

The severity of alcohol use disorders (AUDs) has recently been connected to microbiome changes, suggesting that the gut microbiome may play a role in the development of AUDs. The act of consuming an excessive amount of alcohol quickly is known as binge drinking. Binge drinking is frequently seen in the critical adolescent growth stage. In AUD, as well as a myriad of dietary behavioral disorders, a significant relationship between microbiome composition and socioemotional functioning has also been found. In this study by Carbia et al. (2023), the authors examined a population of 71 young individuals (ages 18 to 25) to explore the possible relationships (and their predictive values) between the changes in microbial profile caused by alcohol and social cognition, impulsivity, and desire. Firstly, study participants completed a neuropsychological assessment. Next, at baseline and three-month marks, craving was assessed while the diet was taken into account. To investigate inflammation, kynurenine, and cortisol, samples of blood, saliva, and hair were collected. Analysis of the results revealed that cravings and changes in the microbiome's composition and neuroactive potential over time were strongly correlated with binge drinking. Excessive drinking was found to lead to specific microbiome changes and issues with emotional awareness. Several microbiome species have been linked to emotional processing and impulsivity. The authors demonstrate through their findings the changes observed in the gut microbiota of young binge drinkers (BDs) and pinpoint the earliest desire signals. The authors discuss that their results may have implications for novel gut-derived therapies aimed at reducing early alcohol-related changes during the vulnerable adolescent years. The rising body of research on the gut microbiome as a regulator of social cognition is further supported by associations between emotional processing and microbiome makeup. [NPID: Microbiome, social cognition, binge drinking, adolescence, gut brain axis]

The inclusion of fermented foods in dietary intake, in addition to dietary fiber, was shown to enhance physical, gut, and mental health by enhancing the gut microbiome. Similarly, the role of a healthy gut diet in ameliorating depression is gaining academic attention. In this cross-sectional study by Lai & Boag (2022), the authors used data from the National Health and Nutrition Examination Survey (2011–2018) on 16572 participants to examine the links between health, diet, and depression. The participants were asked to report their body mass index (BMI) and had their diet, BMI, and depression status evaluated (9-item Patient Health Questionnaire for depression). Pathway analysis of the data revealed that subjective physical health (self-reporting of BMI) and objective physical health (professional measurement of BMI) moderated the links between mild symptoms of depression and dietary variables. Dietary intake of probiotics and fibers led to a substantial reduction in depressive symptoms. Subjective physical health substantially moderated the links between reducing the odds of severe depression and elevated dietary fiber intake. The authors conclude that their results highlight the reduction in depressive symptoms that can be brought forth by gut health-promoting dietary patterns through enhancing physical health, suggesting that dietary interventions may be used to augment or substitute current treatments used in the management of depression. [NPID: Depressive symptoms, gut health, diet, dietary fiber, probiotic, psychobiotics, BMI]

Depression continues to affect individuals across the world in a continuously rising trend. This has prompted research efforts to understand the biological and molecular mechanisms involved in the pathology of depression, bringing forth the use of the gut microbiome as a potential intervention method. In this study by Radjabzadeh et al. (2022), the authors utilized data from the Rotterdam Study cohort (n = 1054) and the Amsterdam HELIUS cohort (n = 1539) to investigate the gut microbiome composition and diversity in the presence of symptoms of depression. Analysis of the data revealed an abundance of specific bacterial taxa in depressed individuals, recognized for producing butyrate, glutamate, gamma amino butyric acid (GABA), and serotonin (known neurotransmitters involved in depression). These taxa included Coprococcus, Subdoligranulum, Eggerthella, Sellimonas, Hungatella, Lachnoclostridium, Eubacterium ventriosum, Ruminococcaceae (UCG002, UCG003, and UCG005), Ruminococcusgauvreauiigroup, Lachnospiraceae (UCG001), and family Ruminococcaceae. The authors conclude that their results demonstrate the presence of a relationship between depression and gut microbiome composition. [NPID: Gut microbiome, diet, depression, neurotransmitters]

The gut microbiome is known to influence host physiological functions, including feeding behaviors. Feeding behaviors are subject to several extrinsic and intrinsic factors such as food palatability, genetic background, and environmental factors. In this study by Ousey et al. (2022), the authors investigated whether feeding behavioral responses to palatable food are controlled by interactions with the gut microbiome, and found that the loss of the gut microbiome through antibiotic depletion (ABX) led to an increase in palatable food consumption in mice, and increased their seeking behaviors to palatable food (high-sucrose pellets) without impacting overall feeding dynamics. This was further explained by an increase in cerebral mesolimbic activity, which is responsible for reward-seeking and motivation behaviors following the consumption of palatable food. On the other hand, restoration of the gut microbiome through fecal transplantation reversed the derangements seen in feeding behavior. Upon analysis of the gut microbiome taxa, the authors noted that S24-7 bacteria and the genus Lactobacillus were abundantly found in mice that did not seek palatable high-sucrose pellets and that colonizing ABX mice with S24-7 and Lactobacillus johnsonii reversed their palatable food-seeking behaviors. The authors conclude that modulating the gut microbiome through extrinsic factors can help decrease palatable food-seeking behavioral responses in mice. [NPID: Gut microbiome, gut microbiota, feeding behavior, hedonic feeding, mesolimbic system, binge eating, antibiotics, fecal microbiota transplantation, Lactobacillus]

Recent evidence pointed to the relationship between sleep disorders and the gut microbiome, demonstrating how the microbiome plays a role in overall host health, owing to the role of sleep in psycho-social health maintenance, weight management, and hormone levels. Thus, sleep is subject to derangements due to gut microbiome dysbiosis, just like a myriad of metabolic conditions. In this review by Neroni et al. (2021), the authors discuss the available literature investigating the relationship between sleep disorders and gut microbiome dysbiosis. [NPID: Insomnia, intermittent hypoxia, microbiota, OSAS, sleep fragmentation]

Recently, the observed impact of dietary consumption on mental health and the gut microbiome has trended in popularity, however, the evidence on the existence and the extent of psychobiotic impacts of dietary interventions remains insufficient. To that end, Berding et al. (2022) evaluated the impact of a psychobiotic intervention (rich in fermented foods and prebiotics) on the mental health and the gut microbiome of 45 healthy adults (18 to 59 years of age, 63% females). The participants were randomized into two groups, receiving either a control diet (n = 21) or a psychobiotic diet (n = 24) for four weeks, during which stress, diet, and health were evaluated via validated questionnaires, in addition to the collection of urine, fecal and plasma samples to compose metabolic profiles. The authors observed a decrease in both perceived and biological indicators of stress, urinary tryptophan, and fecal lipids with the psychobiotic intervention compared to controls (stress reduction by 32% compared to 17% in the control group). No substantial changes were noted in the population of the gut microbiome, however, the observed changes were found to be related to the reduction in perceived stress. The authors conclude that their results demonstrate the potential of psychobiotic dietary interventions in a population of healthy individuals and that microbiome-focused dietary interventions which favorably enhance the gut-brain-microbiome interactions can hold future promise for use in stress reduction and stress-related pathologies, pending further research to fully understand the interactions concerning diet and microbiome [NPID: Mental health, stress, gut microbiome, dietary intervention, psychobiotic diet, metabolism]

The gut microbiome’s (GM) influence on behavior has been documented in several animal studies, and in turn, the role of diet in altering the GM population and its indirect role in influencing animal behavior. A deficiency of dietary components, in particular, magnesium, has been shown to produce depressive and anxiety symptoms in humans and animals, which is postulated due to causing GM derangements. In this study by Winther et al. (2015), the authors investigated the impact of magnesium deficiency on the behavior of C57BL/6 mice by designing an experiment in which mice were fed either a standard diet or a magnesium-deficient diet (MgD) for six weeks. After that, the behavior of the mice was investigated using the forced swim test (FST), and their metabolism was evaluated using the intraperitoneal glucose tolerance test (GTT) two days after FST. GM population was investigated in tandem with neuroinflammatory metabolic markers derived from mouse hippocampus. The results revealed increased depressive-like behavior (FST immobility), increased neuroinflammatory markers (Interleukin-6), and derangements in GM populations of mice fed MgD compared to controls. Thus, the authors conclude that dietary component deficiency, in particular magnesium, may lead to microbiome-gut-brain axis disparity and the induction of depression. [NPID: Animal models, behavior, depression, gut microbiota, magnesium deficiency]

The gut microbiome-brain axis responds to changes in lifestyle, diet, infection, and antibiotics. Similarly, anxiety and dietary derangements lead to negative physiological impacts that are implicit in altering the gut microbiome. Microbiome derangements impact inflammatory responses, immunity, short-chain fatty acid production, gut permeability, and overall neurological homeostasis. Recent evidence points to a relationship between gut microbiome derangements and the pathology of psychiatric conditions like eating disorders (bulimia nervosa, anorexia nervosa, and binge-eating) and generalized anxiety disorder, which could be alleviated using single or multi-strain probiotic supplements. In this PRISMA-compliant review by Navarro-Tapia et al. (2021), the authors outline microbiome derangements seen in patients suffering from eating disorders and/or generalized anxiety disorders, in addition to the role of probiotics as an adjuvant therapeutic strategy. [NPID: Anorexia nervosa, anxiety, binge eating disorder, bulimia nervosa, dysbiosis, gut microbiota, gut-brain axis, probiotics]

Depression is on the rise and is projected by 2030 to become a top health concern. The underlying pathophysiology behind depression remains to be well understood. Several studies have increased the volume of evidence regarding the relationship between the gastrointestinal tract and brain communication axis, and its role in neuropsychiatric derangements like depression. Understanding the impact of diet and stress on the pathophysiology of depression is critical. In this review by Herselman, Bailey & Bobrovskaya (2022), the authors compiled the most recent body of published findings on the major microbiome constituents, the degrees of microbiome diversity, and the impact of diet on the gut microbiome, in addition to outlining the impact of stress on the relationship between the gut and the brain, examined through the use of animal models. Overall, chronic stress was found to elicit a negative impact on gut and brain health, with microbiome composition derangements observed through animal experiments investigating the impact of stress, whereas prebiotic and/or probiotic supplements were found to ameliorate the observed disturbances and the pathophysiology of depression. [NPID: Animal, depression, diet, gut brain axis, microbiota, pathways, prebiotics, probiotics, stress]

The choice of dietary components leads to a broad spectrum of influence on multiple levels, from individual animals up to ecological and evolutionary systems. However, current research has disregarded the effect gut microbiota may have on animal foraging. This concept is one that has not been sufficiently studied, thus, Trevelline and Kohl (2022) demonstrated through their works how germ-free mice, inoculated with distinct microbiomes cultured from wild rodents that practice naturally occurring feeding behaviors, showed remarkable changes in their dietary behaviors. Specifically, the inoculated mice differed in carbohydrate selection compared to controls. Furthermore, these observed differences were linked to changes in levels of systemic essential amino acids, bacterial tryptophan metabolism, and intestinal morphology. Together, the authors comment that these results show how the microbiome impacts nutritional physiology and dietary preferences. [NPID: Animal behavior, diet choice, gut microbiome]

Aggression, investigation, anxiety, depression, and other social and affective behaviors, are expressed through a complex interplay between several psychological systems, such as the neuroendocrine and the immune systems. Current literature postulates that the gut microbiome is central to behavioral modulation, in that it potentially serves to integrate with various psychological systems. It has been demonstrated that the gut microbiome also communes with the brain through neural and humoral pathways, which presents opportunities for further research concerning the gut-brain axis. The impact of experience (e.g., dietary modifications, psychological stress, and immune system stress) has been investigated as an isolated entity, however, as psychological systems integrate and exert their collective influence, our paradigm has to change as we progress in our understanding of the gut-brain axis, behavioral phenotypes, and the potential clinical consequences of these relationships. To that end, Sylvia and Demas (2018) summarized the available evidence on the critical influence the gut microbiome has on altering social and affective behaviors, in addition to a number of distinct communication mechanisms between the gut microbiome, brain and immune system. [NPID: Cytokines, endocrine system, gut-brain axis, immune system, lipopolysaccharide, microbiome, social behavior]

The gut microbiome exerts a considerable influence on the human brain, in parameters such as stress, anxiety, depression and overall behavioral patterns. This observable microbiome-gut-brain axis is potentially controlled by various methods, including neural, immune and endocrine signaling. The quantity of human studies investigating these interaction patterns remains poor, which compelled Johnson (2020) to explore how the components and heterogeneity of the gut microbiome, influence human personality traits. The author’s investigation showed that the existence of certain bacterial genera was linked to exhibited personality traits. In addition, diversity analyses of the gut microbiome showed that those of us who interact with bigger social networks exhibited increasingly heterogeneous microbiomes, leading to the assumption that diverse social interactions play a role in the diversity of the gut microbiome. On the other hand, anxiety and stress correlated with a reduction of microbiome heterogeneity, coupled with a change in microbiome constitution. The author concludes that these results present a new layer in the relationship of personality and how the microbiome-gut-brain axis would possibly contribute to behavioral variability in both healthy adults and psychiatric patients. [NPID: Gut microbiome, human personality, metagenomics, microbiome–gut–brain axis, social behavior]

Current literature postulates that the traits energy and fatigue are distinct unipolar temperaments with definite mental and physical elements (where traits i.e., subjective characteristics of thought and behavior). In this exploratory study by Boolani et al. (2022), the interaction between mental energy (ME), mental fatigue (MF), physical energy (PE), physical fatigue (PF), and the gut microbiome was explored in 20 subjects (31 ± 5 y, physically active, BMI 26.4 ± 4.4 kg/m2) using an online survey, with data on the gut microbiome and metabolome acquired through 16 S rRNA and untargeted metabolomics analyses. Microbiome investigation revealed that Bacteroidetes (45%)—the most notable microbiome phylum—impacted PF negatively, while Firmicutes (43%), the second most notable and butyrate-producing phylum, had members that influenced each of the four traits investigated. Anaerostipes had a two-pronged impact on several traits, with a positive effect observed on ME and a negative effect observed on MF and PF. The authors further observed that, in regards to how diet impacts the components of the gut microbiome, only one food group (processed meat) was found to influence all four moods investigated, with a positive impact on MF and PF, and a negative impact on ME and PE, and that only the Firmicutes genus Holdemania was found to be influenced by processed meat. The authors conclude that in spite of observing perceptible metabolic profiles that did not pose notable implications on the traits studied, the results postulate how energy and fatigue are perceived as distinct traits, whereby bacterial communities —which are not influenced by diet—could help define. Further research is necessary to verify these initial results. [NPID: Gut microbiome, gut microbiota, trait mental fatigue, trait physical fatigue, energy]