In a recent study of 40 women it was found that quantifiable differences of regional brass mass and emotional health was found linked to specific bacterial species. The two species of bacteria that were primarily investigated were Bacteroides and Prevotella. Those women with greater recorded amounts of Prevotella species were found to have greater differences in emotion, attention, and sensory regions of the brain. The women with greater measures of Bacteroides were found to show greater development of the frontal lobe, cerebellum, and hippocampus region of the brain.1
Understanding the Microbiome
The human body is host to trillions of tiny organisms that have been shown to play an integral role in vital processes. These may range from disease prevention to vitamin and mineral production. There exist bacteria that are considered ‘good’ and those considered ‘bad’. Modern Science is still lacking in the ability to fully describe the role of bacteria in maintaining long term health, but many consider its role of great importance. There is an existing understanding of the overall impact of gut health on the brain, and how it may attribute to certain mental and emotional disorders such as Autism and Schizophrenia. 2 Supportive of this notion is the commonality of gastrointestinal disorders such as irritable bowel syndrome (IBS) with conditions such as anxiety and major depressive disorder. 3 Furthermore, current research understands there to be a direct connection between the gut and brain, though a dynamic system referred to as the gut-brain axis (GBA). The GBA is a two-way means of communication between the central nervous system, and the digestive nervous system. This effectively links brain activity with digestive function, though specific dynamics and influences aren’t currently well understood. 4 Broadly speaking it seems reasonable to assert this connection supports the case for digestive function in the role of mental health. This recent research by Dr. Kirsten Tillisch and her team at the University of California have helped to better understand some of the subtle influences of this connection.
This study was conducted among 40 non-obese woman aged 18-55 of whom were recruited through advertisement methods. Before admittance into the study, each woman underwent an extensive physical exam, psychiatric screening, and overview of prior medical conditions. Women that reported having used antibiotics or probiotics were excluded from participation, as were those with a tobacco dependence, pregnant or lactating, currently diagnosed with a psychiatric disorder, or those engaging in 8 or more hours of exercise per week. Additionally, anyone reporting the use of antidepressants or the use of opioids were excluded from the study.
Part of this study was designed to investigate physical attributes of brain structure. These data were gathered through the use of MRI. Stool samples were gathered for DNA microbial analysis to investigate species-specific differences among the participants. These collected samples were analyzed by a third party laboratory in Belgium and standardized in a many to most-accurately categorize differing composition. In addition to the initial MRI scans and subsequent fecal analysis, researchers also gathered data from fMRI (think real time MRI) machines while showing participants emotionally-triggering imagery. This approach was designed to measure regional responses and intensity of responses to emotional stimuli to better understand how differing bacterial species found in the gut may affect neural emotional processing.
After reconciling data between those observed parameters, researchers found that 7 participants fell into the category of having higher levels of Prevotella bacteria and 33 were higher in Bacteroides. The Prevotella group were recorded as having a higher negative response after viewing negative images, though no difference was seen for positive imagery. This was attributed to lessened activity within the hippocampal region, as recorded by fMRI data. Researchers were able to successfully identify participants group role by analyzing brain structure—suggesting an integral role between neural formation and bacterial presence. Most previous work of this nature has been conducted on laboratory mice. Having this human model offers strong support for future work endeavoring to better illustrate the connection between brain and gut. This research found higher levels of Prevotella bacteria to be a accurate prediction of stronger negative emotions and also differing regions of the brain associated with them. This conclusion supports the notion that dietary and environmental influences on microbiota composition likely have an integral role in both emotional processing and neural development.
Bacteroides and Prevotella are the two most prevalent genera (broad types) of bacteria thought to exist in the human digestive tract. Long term dietary composition has been attributed gut microbial diversity. This means that the foods you eat on regular basis contribute to which type of bacteria you may have more of in your gut. A 2011 study title Linking Long-Term Dietary Patterns with Gut Microbial Enterotypes 5 found that noticeable shifts in microbial composition can be observed after as little as 24 hours. This shift was seen in the adoption of either a high fat/low fiber or low fat/high fiber diet. This study found that higher levels of Prevotella bacteria were associated with diets high in carbohydrates, sugar, glucose, and dairy proteins such whey. Diets high in amino acids, animal proteins, choline, long chain fatty acids, GLA, DHA, Calcium, Zinc, and several other vitamins were found to be much more likely to produce Bacteroides weighted states of intestinal composition.
This suggests that diets high in fat and protein are more conducive of Bacteroides bacteria and less so of the [now] negative-emotion linked Prevotella. Excluding all other health factors, this portrays an interesting link between diets high in carbohydrates and plant-based fibers with negative emotional responses. Taking into account the data from both of these studies suggest that diets low in plant fibers, carbs, and sugars are likely more conducive to stable emotional states. This data is far from conclusive, but interesting none the less. Modern scientific investigation has been discovering a deep connection between the brain and gut. The two-way communication between the two, and the now-linked attribution of negative emotions with bacterial composition make a strong argument for heavy consideration of diet and it’s role in mental health.
- http://journals.lww.com/psychosomaticmedicine/Abstract/publishahead/Brain_structure_and_response_to_emotional_stimuli.98803.aspx ↵
- https://www.ncbi.nlm.nih.gov/pubmed/26760398 ↵
- https://www.ncbi.nlm.nih.gov/pubmed/23910373 ↵
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367209/ ↵
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3368382/ ↵