The effect of Probiotics on our health

Bacteria, viruses and fungi are collectively called microbes or micro-organisms, and there are more inside us than we can imagine. It is surprising to know that for each one of our human cells it is estimated that there are 10 much smaller microbial cells! Not all micro-organisms are harmful, in fact this large number of microbes does not disturb our wellbeing, on the contrary, by colonising every place in our body they are living in close association, such that one species benefits without harming the other. In places like our skin, the mouth, nose, genitalia, urinary tract, one can appreciate why it is important to have the right microbial flora…these areas are entry points for otherwise harmful bacteria if left unattended.

Just like ecosystems vary for the oceans, rivers and forests the same applies to the diverse environments in our body which all host a different ecosystem of microbes. Of particular importance is the internal environment of the gastrointestinal tract or intestines. The intestines, also called the gut are populated by about 500 different species of microbe, most of which are non-pathogenic which means that they do not cause disease but it’s not just that, they actually help to protect against disease thus preventing growth of harmful, pathogenic bacteria and thus maintain wellbeing amongst other functions.

Functions of resident bacteria in the gut

In the discovery of penicillin it was found that bacteria do not grow in the vicinity of the Penicillium mould. In the same way, the indigenous flora of the gut competes with invading organisms by producing a number of antibacterial substances including colicins and short chain fatty acids, which are potentially bactericidal and bacteriostatic for their competitors and are therefore considered to inhibit the growth of the invading organisms.

Bacteria lining our intestines help digest food. During digestion, they make vitamins such as biotin and vitamin K that are vital for life. It was found that they play an important role in the production of neurotransmitters. Neurotransmitters are small molecules that are vital in the transmission of signals from one neuron to another in the nervous system.

A particular bacterial species produce an important neurotransmitter, GABA. GABA also plays a role in pain and inflammation. What is surprising is that the molecules produced by bacteria which benefit us are usually by-products of the bacteria’s metabolism or their defence mechanisms.

The microorganisms also ferment unused energy substrates like fibre, and produce hormones to direct the host to store fats so they are very important for digestion.

Another important function is the regulation of the development of the cell layers in the gut – without the resident flora the intestinal wall has been found to be thinner and to contain only a few lymphocytes (white blood cells). Proper development imparts proper permeability to the gut lining which is important in reducing absorption of harmful substances from food.

The symbiotic relationship between the host intestines and microbes has a significant impact on shaping the immune system. To maintain this beneficial relationship, the host immune system should remain hypo-responsive to resident bacteria. However, at the same time, the intestinal immune system has to combat invasive pathogenic bacteria. Thus, the immune system in the intestinal mucosa has very complicated features that are distinct from that in other tissues. The intestinal immune system mounts a strong inflammation against invasive pathogenic bacteria while providing many layers of inhibitory mechanisms not to mount excessive immune response against resident bacteria. The breakdown of such a delicate balance of the intestinal immune system causes the development of inflammatory bowel diseases (IBDs). This implication could be important also in autoimmune diseases.

These communities of microbes are therefore becoming increasingly researched and are now recognised as being almost as important as an organ in our body.


By definition a probiotic is a live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance. Contrasting antibiotics, probiotics are a formulation of selected microbial organisms that result in the growth of microorganisms. In fact some of the best evidence in support of probiotic health benefits is in the treatment of Antibiotic-associated diarrhoea (AAD) where the intestinal microbial balance is lost with the antibiotic and restored with the probiotic. The largest group of probiotic bacteria in the intestine is lactic acid bacteria, of which Lactobacillus acidophilus, found in yoghurt with live cultures, is the best known.

Apart from being available in the form of sachets or capsules containing Lactobacilli (alone or together with Saccharomyces yeast) probiotics are found in other fermented foods such as yoghurt, cheese especially soft cheeses such as gouda, unpasteurised sauerkraut, miso (fermented soybean).

Probiotics are delicate, heat and stomach acid can kill them, rendering them ineffective before they’ve even been digested. Prebiotics on the other hand are specialized plant fibres that beneficially nourish the good bacteria already in the large bowel or colon. The body itself does not digest these plant fibres; instead, the fibres act as a fertilizer to promote the growth of many of the good bacteria in the gut. These, in turn, provide many digestive and general health benefits. Foods containing prebiotics include: asparagus, Jerusalem artichokes, bananas, oatmeal, red wine, honey, maple syrup, and legumes. Consider eating prebiotic foods on their own or with probiotic foods to perhaps give the probiotics a boost.

Current uses

Probiotics can be useful in a number of ailments however, probiotics may be dangerous for people who are immunosuppressed or suffer from serious illnesses. Otherwise it is safe to use probiotics proven in part by the fact that people in cultures around the world have been eating yogurt, cheeses, and other foods containing live cultures for centuries and there is evidence that regular use can actually support a healthy immune system. In fact, one of the ways in which probiotic bacteria’s benefits were discovered is when Lactobacillus Bulgaricus was isolated from yoghurt produced in Bulgaria, where people who consumed it lived longer. The main uses for probiotics are for gastrointestinal disorders.

Uses in gastrointestinal disorders

  • Acute infectious diarrhoea. There is some evidence that probiotics shorten duration of acute diarrhoeal illness, and improve symptoms. Probiotic use in combination with oral rehydration therapy cut the duration of diarrhoea by around 25 hours and the risk of diarrhoea lasting four or more days by 59 per cent.
  • Prophylaxis of antibiotic-associated diarrhoea. There is evidence that probiotics may prevent and treat antibiotic-associated diarrhoea. One potential strategy to prevent this side effect of antibiotics is the concurrent use of probiotic bacteria or yeast. Probiotics are also effective at preventing Clostridium difficile diarrhoea caused by antibiotic treatment.
  • Prevention of traveller’s diarrhoea. The cause of the problem is related to the ingestion of the causative organisms in food and drink upsetting the balance of intestinal microorganisms.
  • Induction or maintenance of remission in Crohn’s disease and ulcerative colitis. These are inflammatory bowel diseases, further research is needed.
  • Irritable bowel syndrome (IBS). There is some evidence that probiotics may improve symptoms of IBS, although on-going studies are needed to identify which patients benefit, and optimal regimens. The National Institute for Health and Care Excellence (NICE) recommends that if patients wish to try probiotics they should take them at a dose recommended by the manufacturer for a minimum of four weeks.
  • Eradication of Helicobacter pylori, a bacterium present in stomach ulcers. A meta-analysis concluded that fermented milk-based probiotic preparations increased eradication rates in patients on standard eradication therapy by 5-15%.

Other possible uses

Many studies are on-going into the possible benefits of probiotics in areas including:

  • Infantile colic.
  • Bacterial vaginosis.
  • Vulvovaginal candidiasis.
  • Prevention of preterm labour.
  • Prevention of recurrent urinary tract infections.
  • Prevention of infant eczema. However, the evidence suggests probiotics are not beneficial in the treatment of eczema.
  • Allergic rhinitis.
  • Fibromyalgia.
  • Treatment of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis.


The human microbiome

The Human Microbiome Project (HMP) is a United States National Institutes of Health initiative with the goal of identifying and characterizing the microorganisms which are found in association with both healthy and diseased humans. The ultimate goal of this and similar NIH-sponsored microbiome projects is to test how changes in the human microbiome are associated with human health or disease.

The term Microbiome has been coined by Joshua Lederberg who argued the importance of microorganisms inhabiting the human body in health and disease. He defines it as “the ecological community of commensal, symbiotic, and pathogenic microorganisms that literally share our body space.”

Each of us begins to assemble a unique congregation of microbes the moment we are born acquiring our mother’s bacteria first and continuing to gather new bacteria from the environment throughout life. It is becoming increasingly clear that the early development and composition of our gut bacteria can influence immunity for life.

Linking disease with bacterial make-up

Scientists have long studied the link between our genes and our health. Now, in a growing area of scientific research, they’re studying the link between the bacteria in our intestines and virtually every disease that ails us. For now, scientists are only making links between a person’s bacterial make-up and the presence of certain diseases. Regardless of whether a cause-and-effect relationship is found, looking at gut bacteria could become a way for doctors to diagnose certain diseases earlier and more accurately.

Research has shown links to allergy, colon cancer, Crohn’s disease, ulcerative colitis, diabetes, obesity, cardiovascular disease and Irritable bowel disorder.


A 2012 study reported by Medical News Today suggested that bacteria residing in the large intestine may slow down the activity of energy-burning brown fat, contributing to the development of obesity.


Findings suggest that delivery via C-section as well as early treatment with antibiotics play an important role in allergies although they are not the sole cause. Also the first observation that significant differences exist in the microbial composition in breast-fed and bottle-fed infants was made a century ago.

Although more research is needed to understand the precise mechanism by which C-section birth and antibiotics lead to allergy, the researchers suspect these two factors precipitate serious shifts in the composition of a baby’s developing gut. Babies born via vaginal delivery are exposed to certain maternal bacteria as they pass through the birth canal. Those bacteria colonise the new-born’s gut and help build immunity. Children born via C-section, however, miss out on this vital initial exposure to bacteria, the researchers say, which may render their immune systems more sensitive to food and other generally harmless substances.

Furthermore, during the first year of life, the gut microbiome undergoes dramatic changes as the infant encounters various microorganisms in the environment. Antibiotics during this critical period may alter gut immunity because the drugs tend to cause collateral damage by wiping out “healthy” bacteria along with disease-causing ones, which can lead to an imbalance between good and bad bacteria in the gut.

Giving probiotics to expectant mothers and newborns could reduce the incidence of allergy, according to researchers from Finland. A 2013 meta-analysis of 25 trials found that probiotic supplementation in pregnancy and early life might help with atopic sensitivity in infants but probably not with asthma or wheezing.

Breastfeeding encourages the growth of beneficial gut bacterial flora and it has also been linked to lower risk of obesity, diabetes, inflammatory bowel disease and allergies later in life.

The exact mechanisms by which probiotics might have an effect is not clear but may be explained by a “discordance” between the initial flora of infants and that of their mothers. The initial gut flora seen in infants in the developing world (and, according to a paper published in 1885, that of 19th century European children) is predominantly the same as that of their mothers. However, this is often not the case now in developed countries, where hospital-acquired organisms predominate in the infant.


More recent research has shown that many autistic patients suffer from gastrointestinal disorders. Studies in a mouse model of autism, published recently in the journal Cell in 2013, showed that autistic mice exhibited gastrointestinal abnormalities, in particular a condition known as intestinal permeability, which allows abnormal passage of substances through the gut wall and into the bloodstream.

The mice were treated with oral doses of Bacteroides fragilis, a bacterium used in probiotic therapy, which alters the gut flora. It was found that after treatment, the permeability was corrected. Furthermore, the mice’s behaviour was also altered. In particular, they were more likely to communicate with each other, and less likely to display repetitive behaviour such as digging. In other words, behaviour associated with autism was reduced.

The researchers are now planning to subject to trial a form of this probiotic treatment on behavioural symptoms in human autism within the next two years.

All references used in this article are available upon request from the author.

This article is not intended to replace a one-on-one relationship with a qualified health care professional and is not intended as medical advice. It is intended as a sharing of knowledge and information.

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