Nutritional Approaches Targeting the Gut Microbiome Could Improve Brain Disorders

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Microbiomes refer to the collective genomes of microorganisms living in a particular environment. Microbiota refers to the community of microbes themselves. For example, the human gastrointestinal tract contains approximately 100 trillion microorganisms (mostly bacteria, but also viruses, fungi, and protozoa). These microorganisms play critical roles in immunity and energy metabolism in humans, ranging from gastrointestinal health to behavior and brain function. However, whether “feeding the microbiome” can help modulate human behavior and brain function is under discussion.

The favorable impact of diets is mediated or moderated via the microbiota-gut-brain axis. Recent studies have highlighted microbiota signatures in the case of psychiatric disorders. This has led to the development of microbiome-targeted therapies called “psychobiotics”. It included administration of live organisms, dietary interventions to reshape microbiome function and composition, and fecal microbial transplants. Of these therapies, the most commonly tested is the administration of probiotic organisms (Lactobacillus and Bifidobacterium strains, alone or in combination) in people with clinical depression.

Research on the impact of dietary therapies, whether comprehensive dietary interventions or specific dietary factors, on the gut microbiome is quite limited. However, the effect of diets can be pervasive and lead to neurodegeneration and neurological development. Thus, modulating the microbiota-gut-brain axis may be an important approach to treat and prevent mental health disorders. However, most of these interventions are at an early stage of research and consideration should also be given to the limitations of these interventions.

A new review published in the Clinical Nutrition and Metabolic Care journal focused on studies that used interventions targeted to the dietary gut microbiota to improve mental health conditions. He also discussed some suggestions for developing more robust and informative interventions for diet and microbiome studies.

Study: Diet and the microbiota-gut-brain axis: an introduction to clinical nutrition. Image Credit: Pikovit/Shutterstock

The microbiota-gut-brain axis

Gut-brain communication primarily involves neuroendocrine-immune pathways sensitive to dietary modulations. Short-chain fatty acids (SCFAs) are most often produced as a result of microbial processing of indigestible dietary fiber. SCFAs can control energy balance, eating behavior and immune functions.

The synthesis of several key neuroactive molecules, such as catecholamines, ϒ-aminobutyric acid (GABA), tryptophan metabolites and serotonin (5-HT), occurs in the gut microbiota. These molecules interact with the autonomic nervous system or stimulate vagal sensory neurons in the gut. This leads to neuronal activation in the nucleus tract lonely (NTS), the place from which information is transmitted to different areas of the brain.

A healthy diet that includes live bacteria or phytochemicals can promote the production of SCFAs and other bioactive compounds that can positively impact metabolic and gastrointestinal health and brain processes. However, a westernized diet including processed foods and high in sugar, salt and saturated fat can alter the composition of the microbiota and lead to low-grade systemic inflammation, which may be associated with metabolic disorders and gastrointestinal pathology. -intestinal, obesity and mental illness.

Impact of gut microbiota-targeted dietary interventions on mental health

Recent studies have suggested that the gut microbiota plays a role in mental health. For example, a lower number of SCFA-producing genera and a higher number of lactic acid-producing bacteria genera have been associated with many different psychiatric disorders. Additionally, recent clinical trials have shown that dietary interventions can improve depression and other symptoms of mental disorders.

The Mediterranean diet is one such diet that has already been reported to be beneficial to health. They were first tested with conventional antidepressant treatment in the ‘SMILES’ trial and were reported to significantly improve symptoms in patients with major depressive disorder. Other studies have also reported that the Mediterranean diet was able to improve symptoms of depression in children and adults. However, most of these studies have focused on behavioral outcomes and not the impact of diet on the gut microbiome.

Fermented foods such as kombucha, kefir, and yogurt have also been reported to improve metabolic and gastrointestinal health. However, studies on their impact on brain and behavioral outcomes are limited. Other diet-related methods to target the microbiota-gut axis include intermittent fasting and ketogenic diets.

How to Design a Diet-Microbiome Behavioral Study

Assessing diet-microbiome-behavioural effects in humans can face different kinds of complexities. One of the most critical challenges is the lack of standardized assessment protocols or dietary interventions.

Approach for dietary intake assessment

Assessment of food intake can be done through direct methods such as duplicate diets, direct observation and nutritional biomarkers or indirect (self-report) methods such as food frequency questionnaires (FFQ), 24-hour food reminders and food diaries. However, all subjective methods depend on the participant’s self-report, perceptions, and experience and can be subject to issues of misreporting and systematic bias.

Objective methods such as nutritional biomarkers are free from misreporting and bias issues. Some nutritional biomarkers include total vitamins and minerals in urine, plasma, serum, energy intake, phytochemicals, caffeine metabolites, isoflavones, carotenoids, and phytosterols. However, using nutritional biomarkers with self-reported data provides optimal results.

Using FFQs to assess dietary intake can have several advantages, such as lower cost, less burden on participants, and rapid, automated data analysis. However, being self-reported, it is memory dependent and also limited to the foods provided in the list. It was observed that reporting errors in the case of FFQs were higher than in other methods, such as food diaries. Food diaries also have certain specifications, such as cumbersome data entry, higher workload for participants, and expert dietary human resources. These limitations can be reduced with the help of technology.

Design microbiome-targeted dietary interventions

Attention should be given to various aspects of the design of a microbiome-targeted dietary intervention. Factors such as duration of intervention, magnitude of change in a diet, and microbiota competition are suggested to play an important role. Assessing participants’ baseline diet and eating behavior characteristics is also necessary to understand the impact of the intervention. Finally, the participant must be willing to adhere to dietary changes, which may include unusual cooking methods, new foods, and shopping habits.

Conclusion

Diet and microbiome studies and their impact on brain health is an emerging area of ​​research. Although several studies have shown the effectiveness of diet in regulating the composition of the microbiome which, in turn, improves gastrointestinal disorders, metabolic disorders and mental illnesses, these studies have limitations that require further investigation. additional works. The development of new dietary interventions requires the determination of the optimal duration of the intervention and the respect of dietary specificities. Further research is needed to design new dietary interventions and improve current nutritional guidelines to prevent acute illness.

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