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Unravelling the gut-brain axis

Science is still elucidating the complex pathways of communication between the brain and gut that include hormone signaling, microbial metabolite production and immune system activation.

Undoubtedly, one of the greatest scientific advancements in our lifetime, along with the sequencing of the human genome, is the profiling of the microbiome. Most people have heard the estimate that we are only “10% human” or that foreign bacterial cells outnumber human cells 10 to 1. New data shows that number is closer to a 50:50 ratio. More accurately, we are 50% human.1 The microbiota exhibits all the characteristics and metabolic activity to be officially categorized as its own “organ.”2   

However, our foreign bacteria have 100 times the genetic diversity and potential of our own DNA. This means they have 100 times the genes that can be flipped on and off through various stimuli, like interaction with each other, metabolites, toxins, exercise and diet.3 The genetic output of our microbial population includes the production of proteins that may signal our own genes to act, either turning them on or off.4,5 

In fact, our microbiota produce nearly 30 different kinds of neurotransmitters, identical to the ones we make in our brain; plus, they manufacture and mediate thousands of immune- or inflammation-modulating molecules.6,7,8,9 The far-reaching impact of our symbiotic relationship with our microbiota influences brain, heart and liver health; the development and etiology of allergic and skin diseases; metabolic efficiency; drug pharmacokinetics; and immune and digestive function.10,11 The ability to manipulate this population for our good is a major constituent of epigenetics and personized nutrition.12,13 

The gut is increasingly referred to as the “second brain.” The gut contains more than 100 to 500 million neurons, exceeding the number of neurons found in the spine.8,14,15

The brain is the manager and sorter of all the stimuli we receive from the outside world. We mainly think of this as what we hear, see and touch, but we forget about the vast amount of data processed via the gut.16 It is no wonder that we have long noticed gastrointestinal (GI) complaints associated with depression, anxiety, insomnia and many other diseases we previously thought of as solely “mental” illnesses.17,18,19 Conversely, for nearly a century, many gut diseases, like irritable bowel disease, were described as “nervous disorders.”

The two-way communication between the gut and the brain via the enteral nervous system (ENS) and the vagal nerve is called the “gut-brain” axis.20,21 Science is still elucidating the complex pathways of communication between the brain and the gut that include hormone signaling, microbial metabolite production and immune system activation.22,23 We already know that enteric nervous system hormones and peptides can make their way into circulation, and more importantly, cross the blood–brain barrier acting synergistically to regulate mood, cognitive function, stress, appetite and sleep.24,25

The communication via the gut-brain axis goes both ways. This is especially evident when stress is introduced. Even short-term exposure to stress can impact the microbiota community profile and lead to dysbiosis by altering the relative proportions of the main microbiota families. This dysbiosis in turn influences stress responsiveness, anxiety-like behavior and the set point for activation of the HPA stress axis.26,27,28

New research is also showing multi-directional influences of the microbiota, circadian rhythm and subsequently, sleep and liver function. The balance of microbiota is essential for normal circadian rhythmicity of gene expression in the gut epithelium.29  

The microbiota is a key component modulating the gut-brain axis. Diet and supplementation are primary influencers of microbial balance and gut health. We are also discovering the importance of the early life gut microbiota in shaping later health outcomes.30,31,32 Early studies show that alterations of microbial balance with antibiotics, nutrition, C-sections, and other environmental factors may result in a lifetime of impaired mechanisms related to stress and behavioral modification.33,34

Disturbances of this complex communication system result in a wide range of disorders: obesity, neurodegenerative issues and functional and inflammatory diseases, including everything from cardiovascular disease (CVD) to irritable bowel disorders, to name a few.14,35 

Failing to account for the complex and individualized interaction with the microbiota is probably a major factor in why clinical studies on depressive disorders, weight management and many other conditions famously result in “mixed” outcomes.

The new science surrounding the microbiome provides many opportunities for developing products that can mediate GI function and thereby influence overall health. While probiotics have many potential benefits , emerging science is poised to create a shift in the current probiotics market. It may not validate many of the high-dose, high-strain formulas, and is likely to focus on specific strains for targeted benefits. However, some of the best opportunities to mediate the gut-brain axis include lifestyle factors, like diet, exercise and sleep.36,37 

For consumers and health advocates focused on a more preventive and comprehensive “whole organism” approach to wellness, gut health and the microbiome offer the single most compelling area for self-care. It is in the “whole organism” focus where lifestyle changes are likely to make the most significant difference.

Jennifer Cooper has spent over 25 years in consumer health care and is currently the chief scientific officer at Savant Science (savantscience.com). She has held senior R&D and quality positions in OTC and supplement companies in the US and EU. Jennifer has directed the development of supplements, over-the-counter drugs, homeopathics, functional foods, traditional herbal medicines, medical devices and dermocosmetics. She has developed and brought to market over 300 new products in more than 20 different countries.

Learn more about the microbiome’s impact on cognition from Jennifer Cooper during the “Supporting the Cycle: Solutions to Manage Stress and Improve Sleep” session on Wednesday, Oct. 16 at 1:30 p.m., at SupplySide West in Las Vegas.

 

References

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