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,
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.
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.:)
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