I carry a 2 kg of organisms inside my gut...and I love them!

Wondering if gut bateria can make yu slim or happy? Read this series of articles (3) to find out. A summary of current research - the body is still a plartial mystery...

If you had to dive into the gut (figuratively, of course) research like I did, you would be overwhelmed by the amount of studies related to health in departments like nutrition, immunity and mental health. The gut seems to be the centre of our health, both physical and mental. Studies like such have been going on, intermittently, for a century now. The first studies in the beginning of the 20th centuries have been later abandoned for lack of technological capacity to analyse the different steps involved in such connections and explain the mechanisms. Now, in this era of genetic technological advancement and refined measuring tools, there is a wide group of scientists throughout the world studying and explaining the connection between the gut microbiota and the Host (us).

Gut microbiota or gut microbes, or gut flora is not a forest of microscopic plants but a jungle of unicellular organisms with no nucleus: more than 10 to the power of 14 (= more than one hundred thousand billion, or more than 10 times the cells composing the human body) microorganisms that belong to about 1,000 different species, and more than 7,000 strains of principally anaerobic (living without oxygen) bacteria, among which the gram-negative Bacteroides species comprise the majority (ca. 25 %). Along with the bacteria, also microscopic fungi and yeasts and viruses. A whole separate ecosystem, living inside our digestive tract.

The gut bacteria can have both beneficial and harmful effects on the host, and the final result depends on the balance among the different strains. The health promoting effects of a balanced gut microbiota are:

  • inhibition of growth of harmful bacteria (keeping them in low numbers),

  • stimulation of immune functions,

  • improved digestion,

  • absorption of essential nutrients (including Ca, mg, P),

  • synthesis of vitamins (especially Bs), amino-acids and digestive enzymes,

  • control of satiety and food intake, glucose and fat metabolism (can these bugs keep us or make us slim???).

The gut microbiota is part of the gut-brain axis, a super-system including central nervous system, endocrine (hormonal) system, immune system (defense system), autonomic nervous system (automatic functions), and enteric nervous system. The enteric nervous system is a collection of neurons in the digestive system that constitutes the “brain of the gut” and can function independently of the central nervous system. It controls motility of stomach and intestine, gland secretion for release of digestive juices and hormones, and circulation of the digestive system.

Such gut-brain axis ‘system of systems’ affects most of our functions. It is as if we were existing under the tyranny of a few billion commanders. We feed them, host them, protect them and in exchange they do several services for us.

Let’s see the different departments of their impact on our body…and mind.

Immunity: symbiotic bacteria (living inside us - the host- while giving advantages to the host) need to escape the local immune system to avoid being fought against as pathogens, ie. they need to induce tolerance of the host towards their presence, and they do this by using some microbial products that communicate with the host immune system. For example, one symbiont Bacteroides fragilis produces a polysaccharide A (PSA) that, not only prevents the bacteria to be attacked by our immune system but also regulates host immunity throughout the body. PSA achieves this by causing specific genetic changes on our immune system cells. Also, Lactobacillus plantarum secretes proteins capable of interacting with our immune system cells.

immune ssytem.jpeg

The lymphoid tissue of the gut (the immune defence centre proper of the digestive system) is ‘trained’ by the presence of certain gut bacteria and their products, so that specific white blood cells are in this way primed to fight infections attacking the body. The gut microbiota has all interest in keeping us in good shape since their survivorship depends on ours, like in any symbiotic relationship.

Such immune effects reach the whole organism, included the brain, via blood or lymph circulation.

A messed up, unbalanced microbiota of the gut, in which opportunistic pathogenic microorganisms are not kept in control by our nice symbionts and take the lead, can have serious negative consequence on our health and can even lead to auto-immune conditions. According to the “hygiene hypothesis” regarding the control of immune function, increased vaccination practices, extended usage of antibiotics, and clean environment may alter the colonization of intestinal microorganisms. This could lead to a pro-inflammatory reaction of the immune system, which has been associated with autoimmune conditions such as allergy and asthma.

Bringing the composition of the microbiota to a healthy mix, could help in treating such auto-inflammatory diseases. For example, in multiple sclerosis, an autoimmune disease attacking nervous cells by demyelinating them (stripping them of the myelin sheath that surrounds them), a modification of intestinal symbionts could alter disease outcomes: oral treatment with a polysaccharide derived from Bacteroides fragilis has in fact shown to protect mice against a demyelinating disease of the central nervous system. Such findings are limited to lab mice but carry a lot of promises for treating humans. This is an example of the use of probiotics that we will explore in a next chapter.

A change of the gut microbes can also lead to a weakening of the gut barrier. This creates a cascade of negative effects that we will see in soon.

What is most interesting is the wave of new research that connects our microbes with our mental well-being and health….but this is a long story that will be posted in the near future. Stay tuned.:)

gut bacteria.jpg


Addolorato G, et al.2008 State and trait anxiety and depression in patients affected by gastrointestinal diseases: Psychometric evaluation of 1641 patients referred to an internal medicine outpatient setting. Int J Clin Pract 62:1063–1069.

Akbaraly TN, Brunner EJ, Ferrie JE, Marmot MG, Kivimaki M, Singh-Manoux A. 2009, Dietary pattern and depressive symptoms in middle age. Br J Psychiatry. 2009 Nov;195(5):408-13. doi: 10.1192/bjp.bp.108.058925.

Arnold L 1929 Alterations in the endogenous enteric bacterial flora and microbic permeability of the intestinal wall in relation to the nutritional and meteorological changes. J Hygiene 1929, 29:82–116

Bested et al. 2013 III Intestinal microbiota, probiotics and mental health: from Metchnikoff to modern advances: part III – convergence toward clinical trials, Gut Pathogens 2013, 5:4

Fuller, R. 1989 Probiotics in man and animals. J. Appi. Bacteriol.

66: 365-378._

Gibson, G.R., Roberfroid, M.B.1995 Dietary Modulation of the Human Colonie Microbiota: Introducing the Concept of Prebiotics American Institute of Nutrition.

Ley RE, et al.2008 Evolution of mammals and their gut microbes. Science 320:1647–1651.

Lavasani S, Dzhambazov B, Nouri M, Fak F, Buske S, Molin G, et al. 2010 A novel probiotic mixture exerts a therapeutic effect on experimental autoimmune encephalomyelitis mediated by IL-10 producing regulatory T cells. PLoS One. 2010; 5: e9009.

Lindeberg S. 2012 Paleolithic diets as a model for prevention and treatment of Western disease. Am J Hum Biol 2012, 24:110–115.

Miura H, Ozaki N, Sawada M, Isobe K, Ohta T, Nagatsu T. 2008 A link between stress and depression: shifts in the balance between the kynurenine and serotonin pathways of tryptophan metabolism and the etiology and pathophysiology of depression. Stress 2008, 11:198-209.

Logan, A.C. Martin Katzman 2005. Major depressive disorder: probiotics may be an adjuvant therapy, Medical hypotheses, 64, 3: 533-538 (http://www.medical-hypotheses.com/article/S0306-9877%2804%2900496-7/abstract)

Maes, M., Marta Kubera and Jean-Claude Leunis 2008 The gut-brain barrier in major depression: Intestinal mucosal dysfunction with an increased translocation of LPS from gram negative enterobacteria (leaky gut) plays a role in the inflammatory pathophysiology of depression, Neuroendocronology letters, 29, 1, 117-124

Mohammadi, D. 2015 Could an inflamed brain be a hidden cause of depression?, New Scientist, 29 June 2015

Nikolov RN, et al. 2009 Gastrointestinal symptoms in a sample of children with pervasive developmental disorders. J Autism Dev Disord 39:405–413

Ochoa-Repáraz J, Mielcarz DW, Wang Y, Begum-Haque S, Dasgupta S, Kasper DL, et al. 2010 A polysaccharide from the human commensal Bacteroides fragilis protects against CNS demyelinating disease. Mucosal Immunol. 2010; 3: 487-495.127.

Riaza Bermudo-Soriano C, Perez-Rodriguez MM, Vaquero-Lorenzo C, Baca-Garcia E 2012 New perspectives in glutamate and anxiety. Pharmacol Biochem Behav 2012, 100:752–774.

Sanchez-Villegas, A. and Miguel A Martínez-González 2013 Diet, a new target to prevent depression?. BMC medicine, 11, 3

Seckl JR, Meaney MJ 2004 Glucocorticoid programming. Ann N Y Acad Sci 1032:63–84.

Skarupski,K.A., C.C. Tangney, H. Li, D.A. Evans, and M.C. Morris, 2013 Mediterranean Diet and Depressive Symptoms Among Older Adults Over Time, J Nutr Health Aging. 2013; 17(5): 441–445.

Tsai YC, Chiu Li W, Dowd SE, Scurlock B, Acosta-Martinez V, Lyte M. 2009 Memory and learning behavior in mice is temporally associated with diet-induced alterations in gut bacteria. Physiol Behav 2009, 96:557–567.

Wang, Y. et al. 2014, An intestinal commensal symbiosis factor controls neuroinflammation via TLR2-mediated CD39 Signalling, Nature Communication, July 1014, 5, 4432

Wang, Y. et al. 2014, A commensal bacterial product elicits and modulates migratory capacity of CD39+ CD4 T regulatory subsets in the suppression of neuroinflammation, Gut Microbes 5:4, 1–10

Featured Posts
Recent Posts
Search By Tags

© 2014 by Pura Vita, Proudly created with Wix.com