A recent review published in Nature by a group of researchers from Australia and the United States explored recent advances in our understanding of gut microbiome-host brain interactions. With the growing acceptance of a clear correlation between the gut microbiome and mental health, this field of research is gradually switching from simply identifying relationships between intestinal microbiota and the host physiology to determining the exact nature of these relationships and using this information to examine and predict disease susceptibility, treatment response, and risk reduction.
Multiple studies demonstrate a clear correlation between the gut microbiome and mental health
What shapes our gut microbiome?
The gut microbiome is affected by both external factors including diet, intestinal infections, and exposure to drugs, as well as natural processes, such as enteric pathology or aging. Better understanding of the nature of these exposures may help to develop more effective risk reduction strategies. For example, diet is a widely accepted factor that correlates with both intestinal microbiota and mental health risks. It is now well established that sugars and saturated fats (major components of a Western diet) may lead to a reduced gut barrier function and increased risks of a mental health disease. On the other hand, foods that promote biosynthesis of short-chain fatty acids (SCFAs) are linked with reduced neuroinflammation. A recent study that analyzed 14,000 university graduates in Spain found a significant correlation between ultra-processed foods (defined here as energy-dense, ready-to-consume industrial formulations, which typically contain little or even no intact food, and are depleted in dietary fiber, micronutrients, and other bioactive compounds) and depression. Several other studies also reported that maternal diet plays an important role in “shaping fetal and early postnatal development, including immune maturation and brain development”.
Can we predict treatment responses?
A number of research articles published over the last few years agree on the fact that the gut microbiome has a considerable influence on brain physiology and mental health. For example, researchers have detected relationships between the intestinal microbiota with multiple sclerosis, schizophrenia, autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (see references [2-13] in Shoubridge, et al., 2022 for more information). These studies also raise an important question as to whether this knowledge may help to better predict responses to therapy in a clinical setting.
How to improve mental health via microbiome-targeted interventions?
Several strategies can be used to improve mental health via modification of the gut microbiome. The two most widely used approaches include direct modification of the gut microbiota and microbiome metabolic output through the introduction of probiotics or the use of dietary or prebiotic strategies. As of now, our knowledge and evidence in support of specific pre- and probiotics remains limited. In addition, the remarkable complexity of the microbiome–host interactions makes assessing the precise effects of dietary changes at a population level challenging. However, some large scale international studies identified clear connections between dietary exposure and mental health risk factors. For example, a European study from 2020 investigated the effects of a 12-month Mediterranean diet on more than 600 elderly subjects (65–79 years old). The researchers found more bacteria positively associated with lower frailty and improved cognitive function and negatively associated with inflammation. Overall, the results from this study indicate a clear positive effect of following a healthy diet on both the gut microbiome and general mental health.
The results indicate a positive effect of following a healthy diet on both the gut microbiome and general mental health
Despite considerable progress achieved in the gut microbiome–brain field over the last decade, we are far from a complete understanding of all the nuances of this highly complex and intricate system. The authors of the Nature review highlight the necessity of conducting further large human cohort studies that take into account the so-called ‘three-hit’ model in which the possibility of mental health issues is examined through the prism of genetic predisposition, the prenatal environment, and later life experiences.
Reference:
Shoubridge, Andrew P., et al. "The gut microbiome and mental health: advances in research and emerging priorities." Molecular psychiatry 27.4 (2022): 1908-1919.
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