Introduction to Probiotics

Probiotics, including bacteria and yeast, are live microorganisms that have demonstrated beneficial effects on human health. Probiotics are described as living microorganisms that, when ingested, provide a health benefit. Your gut is home to a complex eco-system of 300–500 bacterial species. The bacteria comprising the microbes in your body are said to outnumber your own body cells at a ratio of 10-to-1 [i] [ii].

The general health benefits of probiotics

Most of this bacteria reside in the intestinal tract and serve many purposes such as converting ingested substances into those which can be used to promote health [iii]. Some vitamins such as vitamin K and some B vitamins are produced by gut bacteria, for example [iv]. It has been documented through many clinical trials that probiotics could shape the intestinal microbiota leading to potential control of multiple bowel diseases and promotion of overall wellness [v]. Probiotics should not be confused with prebiotics, which are non-digestible food ingredients, namely carbohydrates and fibres that confers benefits on the host by selectively stimulating a group of bacteria in the colon with beneficial probiotic properties.

Historically, probiotic, is a word derived from Latin, meaning 'for life'. A long time before the awareness of probiotic microorganisms, fermented products, such as beer, bread, wine, kefir and cheese had been frequently used for nutritional and therapeutic purposes. The history of probiotics goes parallel with the evolution of human race and, can be traced back to the ancient times, nearly 10,000 years ago [vi].

The most common probiotic bacteria are Lactobacillus and Bifidobacteria. Other common kinds are Saccharomyces, Streptococcus, Enterococcus, Escherichia, and Bacillus.

Brain health

The human gastrointestinal (gut) microbiota comprises diverse and dynamic populations of bacteria, archaea, viruses, fungi, and protozoa, coexisting in a symbiotic relationship which is beneficial to both organism and host. The blood-brain barrier serves an immune function to protect brain cells and regulate the brain's microenvironment. The gut microbiota is proposed to contribute to blood-brain barrier and against the development of diseases causing degeneration of brain function. As such, strategies to control gut bacteria could be used as a therapeutic aid for promoting and restoring brain health [vii]. It is thought an imbalance of gut bacteria could influence brain disorders including Autism spectrum disorders and neurodegenerative disorders[viii] .

Gut health

There is high-quality evidence that probiotics are effective for acute infectious diarrhoea, antibiotic-associated diarrhoea, ulcerative colitis, irritable bowel syndrome and other disorders of the digestive system [ix]. Supplementing with probiotics is said to influence cells lining the gut and immune cells in systems known as gut-associated lymphoid tissue (GALT), which works to protects us from ingested microbes. The gut flora also turns fibre into short-chain fats like butyrate, propionate, and acetate, which feed the gut wall and help to perform many metabolic functions [x]
[xi]. Short chain fatty acids also stimulate the immune system and strengthen the resilience of the gut wall. This action can help prevent unwanted substances from entering the body via the blood and provoking an immune response, an example includes common food allergens such as dairy or gluten [xii]
[xiii].

Metabolic health and cardiovascular health

Dysbiosis is the term used to describe a microbiome out of balance and where non-beneficial bacteria thrive. Such cases of gut dysbiosis have been linked obesity and type 2 diabetes [xiv].

Heart disease is also said to be implicated by the state of the gut microbiome, a gut high in beneficial bacteria is also said to lower blood pressure and cholesterol and create a healthier balance of ‘good’ to ‘bad’ cholesterol [xv].

Immune benefits

We have evolved with microbes therefore our immune systems are tailored to our surroundings. The development of our innate immune system, the non-specific branch of the immune system that protects the body from all potential disease causing microbes and substances, coincides with the emergence of microbial colonisation in the body at a young age [xvi]. A large proportion of this initial exposure to microbes as infants occurs via ingested microbes in food.

The relationship between commensal microbes and their hosts has been studied for many years. Commensal bacteria act on the host's immune system to induce protective responses that prevent over-growth and invasion by disease causing microbes (known as pathogens). As such, commensal bacteria can control the growth of pathogens through competition for similar energy sources and production of anti-microbial molecules to kill surrounding microbes [xvii].

Meanwhile, the host’s immune system is important in determining the composition of the microbiota. It is said the immune systems of the gut and the immune systems in other areas of the body interact [xviii].

Immune systems communicating with the gut immune system include Lymphoid tissues. Bone marrow and the thymus are primary lymphoid tissues and the sites of white blood cell (immune cell) development. The lymph nodes, spleen, tonsils and Peyer's patches are examples of secondary lymphoid tissue [xix]. Gut-associated lymphoid tissue
(GALT), is dependent on the microbiota after birth [xx].

Additionally, the microbiota are also essential for the development of the mucosal immune system, situated in the lining of the gut. This immune system interacts heavily with the species of the gut microbiota to continue its function. As mentioned previously the mucosal immune system is very important as it is the first line of defence, a physical barrier against invading disease -causing microbes [xxi].