The microbiome and gut health

The human gut microbiome and its role in health are the subject of extensive and ongoing clinical research. What we do know is that the microbiome is involved in fundamental metabolic, nutritional and immune system functions. That’s why it is so important to protect the microbiome and support its continued healthy balance.¹Bull MJ and Plummer NT. The human gut microbiome in health and disease. Integr Med 2014;13(6):17-22.

The microbiome and gut health

So what exactly is the gut microbiome?

The human microbiota consists of the 10-100 trillion symbiotic microbial cells harboured by each person, primarily bacteria in the gut; the human microbiome consists of the genes these cells harbour.²Ursell LK, et al. Defining the human microbiome. Nutr Rev 2012;70(1):S38-S44. A typical digestive tract contains a vast collection of microbial communities, including:³Sender R, et al. Revised estimates for the number of human and bacteria cells in the body. PLOS Biology 2016;14(8):e1002533.

Bacteria

Yeasts

Viruses

Archaea

Fungi

The gut contains more than 1000 bacterial species. And that’s a good thing, because a diversity of bacteria in the gut is associated with stability and resilience, which is a reliable indicator of gut health.⁴McBurney MI, et al. Establishing what constitutes a healthy human gut microbiome: state of the science, regulatory considerations, and future directions. J Nutrition 2019;149(11):1882-1895. And, interestingly, research has shown that the composition of the gut microbiome can change with dietary intervention,⁵So D, et al. Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis. Am J Clin Nutrition 2018;107(6):965-983. stress levels⁶Conlon MA and Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients 2015;7(1):17-44. and quality of sleep.⁷Benedict C, et al. Gut microbiota and glucometabolic alterations in response to recurrent partial sleep deprivation in normal-weight young individuals. Mol Metab 2016;5(12):1175-1186.

Differentiating between ‘microbiome’ and ‘microbiota’

Based on the recent advances in the area, a paper published by Berg et al⁸Berg G, et al. Microbiome definition re-visited: old concepts and new challenges. Microbiome 2020. 8:103. p. 1-22. on June 30th 2020 recommends the revival of the original definition of the microbiome term suggested by Whipps et al.⁹Whipps J, Lewis K, Cooke R. Mycoparasitism and plant disease control. In: Burge M, editor. Fungi Biol Control Syst. Manchester University Press; 1988. p. 161-187 Berg et al explain that, ‘The definition, which contains all important points that are valid even 30 years after its publication in 1988, was extended by two explanatory sentences differentiating the terms microbiome and microbiota’:

Definition of microbiome

The microbiome is defined as a characteristic microbial community occupying a reasonably well-defined habitat which has distinct physio-chemical properties. The microbiome not only refers to the microorganisms involved but also encompass their theatre of activity, which results in the formation of specific ecological niches. The microbiome, which forms a dynamic and interactive micro-ecosystem prone to change in time and scale, is integrated in macro-ecosystems including eukaryotic hosts, and here crucial for their functioning and health.

Definition of microbiota

The microbiota consists of the assembly of microorganisms belonging to different kingdoms (Prokaryotes [Bacteria, Archaea], Eukaryotes [e.g., Protozoa, Fungi, and Algae]), while “their theatre of activity” includes microbial structures, metabolites, mobile genetic elements (e.g., transposons, phages, and viruses), and relic DNA embedded in the environmental conditions of the habitat.

What influences the balance of the gut microbiome?

Gut microbiota are unique to each individual. Their composition is influenced by various factors – some of which we can control, and others we can’t.

For example, when a baby is born, the delivery method can influence maternal-offspring exchanges of microbiota. In the womb, if the unborn baby is exposed to antibiotics, this can also affect their gut microbiome.¹⁰Mueller NT, et al. The infant microbiome development: mom matters. Trends Mol Med 2015;21(2):109-117.

Throughout life, people can support the balance of their gut microbiome by making healthy lifestyle choices, such as the food they eat and how much exercise they get.¹¹Quigley E. Gut microbiome as a clinical tool in gastrointestinal disease management: are we there yet? Nat Rev Gastroenterol Hepatol 2017;14:315-320.

For more information about factors that influence the balance of the gut microbiome, please download our gut microbiome factsheet.

The role of the microbiome in health and illness

In healthy bodies, the gut microbiota perform a number of key functions:

Metabolism
Fermenting non-digestible food components (mainly dietary fibre) to produce short-chain fatty acids that are important for maintaining a healthy colon¹²Gill PA, et al. Review article: short chain fatty acids as potential therapeutic agents in human gastrointestinal and inflammatory disorders. Aliment Pharmacol Ther 2018;48(1):15-34.
Synthesis of essential nutrients, including B vitamins¹³Magnusdottir S, et al. Systematic genome assessment of B-vitamin biosynthesis suggests co-operation among gut microbes. Front Genet 2015;6:148.
Release/stimulation of important neurotransmitters, such as dopamine and serotonin¹⁴Cryan JF, et al. The microbiota-gut-brain axis. Physiol Rev 2019;99(4):1877-2013.

Metabolism

Fermenting non-digestible food components (mainly dietary fibre) to produce short-chain fatty acids that are important for maintaining a healthy colon¹²Gill PA, et al. Review article: short chain fatty acids as potential therapeutic agents in human gastrointestinal and inflammatory disorders. Aliment Pharmacol Ther 2018;48(1):15-34.
Synthesis of essential nutrients, including B vitamins¹³Magnusdottir S, et al. Systematic genome assessment of B-vitamin biosynthesis suggests co-operation among gut microbes. Front Genet 2015;6:148.
Release/stimulation of important neurotransmitters, such as dopamine and serotonin¹⁴Cryan JF, et al. The microbiota-gut-brain axis. Physiol Rev 2019;99(4):1877-2013.

Immunity
Gut-associated lymphoid tissue is highly specialised and is the main entity of mucosal-associated lymphoid tissue, representing ~70% of the entire immune system
Gut microbiota inform the immune system in establishing a balance between tolerating/responding to potential threats¹⁴Cryan JF, et al. The microbiota-gut-brain axis. Physiol Rev 2019;99(4):1877-2013.

Immunity

Gut-associated lymphoid tissue is highly specialised and is the main entity of mucosal-associated lymphoid tissue, representing ~70% of the entire immune system
Gut microbiota inform the immune system in establishing a balance between tolerating/responding to potential threats¹⁴

Protection
The microbiota act as a structural barrier, preventing pathogen adhesion and subsequent colonisation¹⁵Iacob S, et al. Intestinal Microbiota as a Host Defense Mechanism to Infectious Threats. Front Microbiol 2018;9:3328.

Protection

The microbiota act as a structural barrier, preventing pathogen adhesion and subsequent colonisation¹⁵Iacob S, et al. Intestinal Microbiota as a Host Defense Mechanism to Infectious Threats. Front Microbiol 2018;9:3328.

Understanding dysbiosis

When the microbiome becomes imbalanced, this is known as ‘dysbiosis’ and can be defined as:¹⁶Petersen C and Round JL. Defining dysbiosis and its influence on host immunity and disease. Cellular Microbiol 2014;16(7):1024-1033.

An increase in potentially harmful microbes
Loss of microbial diversity
Loss of beneficial microbes

Dysbiosis can be implicated in the pathophysiology of gastrointestinal disorders¹⁷Pittayanon R, et al. Gut microbiota in patients with irritable bowel syndrome – a systematic review. Gastroenterology 2019;57(1):97-108.^,¹⁸Nishida A, et al. Gut microbiota in the pathogenesis of inflammatory bowel disease. Clin J Gastroenterol 2018;11(1):1-10. and other metabolic conditions.¹⁹Vallianou N, et al. Understanding the role of the gut microbiome and microbial metabolites in obesity and obesity-associated metabolic disorders: current evidence and perspectives. Current Obesity Reports 2019;8(3):317-332.

What causes dysbiosis?

Dysbiosis may be caused by medication (e.g. antibiotics),²⁰Maier L, et al. Extensive impact of non-antibiotic drugs on human gut bacteria. Nature 2018;555(7698):623-628.^,²¹Lange et al. Effects of Antibiotics on Gut Microbiota. Digestive Diseases. 2016;34:260-268.bacterial infections (e.g. gastritis),²²Iacob S and Iacob DG. Infectious threats, the intestinal barrier, and its Trojan horse: dysbiosis. Front Microbiol 2019;10:1676. stress,²³Clapp M, et al. Gut microbiota’s effect on mental health: the gut-brain axis. Clin Pract 2017;7(4):987.and lack of sleep.²⁴Parkar SG, et al. Potential role for the gut microbiota in modulating host circadian rhythms and metabolic health. Microorganisms 2019;7(2):41.

To find out more, please download our factsheet about how the gut microbiome affects health, including links to key review papers.

The link between the gut and the brain

Unlike with other organs of the body, communication between the gut and the brain appears to be a two-way affair. This two-way communication is believed to occur via various routes.²⁵Liang S, et al. Gut-brain psychology: rethinking psychology from the microbiota-gut-brain axis. Front Integr Neurosci 2018;12:33.

Neural

Vagus nerve and spinal cord

Endocrine

HPA axis

Immune system

Production of cytokines

Metabolism

Short-chain fatty acids interact with enteroendocrine cells to produce neuropeptides

How people can support their own gut microbiome health

There are various lifestyle factors that can influence the health of the gut microbiome. These include:

Diet

In terms of diet, variety and diversity are key. The focus should be on plant-based nutrition, and should include polyunsaturated and monounsaturated fats, and proteins from foods such as fish, poultry, beans and nuts. Artificial sweeteners and alcohol should be consumed in moderation. Experimenting with fermented foods is recommended, for example cultured milk products and yogurt.²⁶Singh RK, et al. [Influence of diet on the gut microbiome and implications for human health. J Transl Med 2017;15:73. Food supplements containing live bacteria are also a popular way of supporting the microbiome. For more information on what to recommend to your patients, download our nutrition and the microbiome article – written by registered dietitian Laura Tilt.

Exercise

Lack of exercise may have an important influence on shifts in microbial populations. A study showed that professional athletes had an increase in the diversity of their gut microbial populations in response to exercise and diet.⁶Conlon MA and Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients 2015;7(1):17-44.

Symprove metal health tips for a healthy microbiome

Stress levels

Stress has an impact on colonic motor activity via the gut-brain axis, which can alter gut microbiota profiles.⁶Conlon MA and Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients 2015;7(1):17-44. Activities such as yoga and meditation have been demonstrated to reduce the effects of stress on the body.²⁷Pascoe MC, et al. Yoga, mindfulness-based stress reduction and stress-related physiological measures: a meta-analysis. Psychoneuoroendocrinology 2017;86:152-168.^,²⁸Cahn BR, et al. Yoga, meditation and mind-body health: Increased BDNF, cortisol awakening response, and altered inflammatory marker expression after a 3-month yoga and meditation retreat. Front Hum Neurosci 2017;11:315. People who wish to help promote a healthy balance of their gut microbiome may find using techniques such as yoga and meditation to reduce their stress levels beneficial.

Symprove sleep tips for a healthy microbiome

Quality and quantity of sleep

A study has shown that short-term sleep loss induces subtle effects on the human microbiota.¹⁰Mueller NT, et al. The infant microbiome development: mom matters. Trends Mol Med 2015;21(2):109-117. This points to the role of sleep in gut health. Good quality sleep is an integral part of a healthy lifestyle. And a healthy diet, regular exercise and techniques to reduce stress all contribute to enjoying a better quality of sleep.

Smoking

Smoking has a significant negative influence on gut microbiota composition.⁶ Conlon MA and Bird AR. The impact of diet and lifestyle on gut microbiota and human health. Nutrients 2015;7(1):17-44. Therefore, alongside all the other known health reasons to quit, the best advice is to aim to give up smoking as soon as possible to help promote a healthy gut microbiome. People should consult their doctor if they need assistance in quitting.

Recommending a food supplement to help balance bacteria in the gut

Alongside recommending a healthy diet and lifestyle, food supplements can be used to help promote a healthy balance of bacteria in the gut.

Recommending a food supplement to help balance bacteria in the gut

Female nutritionist talking to a client about Symprove

Alongside recommending a healthy diet and lifestyle, food supplements can be used to help promote a healthy balance of bacteria in the gut.

There are certain things to consider when recommending a food supplement:²⁹International Scientific Association for Probiotics and Prebiotics. Probiotic checklist: making a smart selection, 2018. Available at: https://isappscience.org/isapp-releases-new-infographic/. Accessed December 2019.^,³⁰World Health Organization (WHO). Guidelines for the Evaluation of Probiotics in Food 2002. Available at: https://www.who.int/foodsafety/fs_management/en/probiotic_guidelines.pdf. Accessed December 2019.

Has it demonstrated a benefit in clinical trials and in the population of interest?
Does it provide an effective dose, as shown by research studies that have used the product?
Is it adequately labelled with:
Full strain names, e.g. Lactobacillus acidophilus NCIMB 30175 Concentration Storage instructions Administration instructions Recommended dose

Has it demonstrated a benefit in clinical trials and in the population of interest?

Does it provide an effective dose, as shown by research studies that have used the product?

Is it adequately labelled with:

Full strain names, e.g. Lactobacillus acidophilus NCIMB 30175
Concentration
Storage instructions
Administration instructions
Recommended dose

Is the strain level fully characterised?
Has its viability and functionality through the gut been established?
Does it contain any ingredients that may be unsuitable for certain people, such as:
Dietary fibre Lactose Added sugars Allergens (e.g. casein)

Is the strain level fully characterised?

Has its viability and functionality through the gut been established?

Does it contain any ingredients that may be unsuitable for certain people, such as: