About probiotics

According to World Health Organization (WHO), probiotics are defined as live nonpathogenic microorganisms that exhibit beneficial health effects on the host (e.g. human or animal) when consumed in adequate amounts (WHO, 2011). Probiotics are now widely available in the form of food and dietary supplements in powdered, liquid and capsule form. Examples of probiotic foods include yoghurt, kefir, kombucha, kimchi, sauerkraut and tempeh.

Probiotics and gut health

It is estimated that there are 1013~1014 of microorganisms inhabiting the human gastrointestinal (GI) tract (Sender et al, 2016), with at least 1,000 different species (Shreiner et al., 2015) forming a mutualistic relationship with the human host. All ‘good’ and ‘bad’ microorganisms that populate the entire gut are called the gut microbiota. The gut microbiota plays an important role in regulating digestion, benefiting the immune system and other health aspects, therefore, it is essential to maintain a good balance of microbiota for good overall health. When this balance is disrupted (otherwise known as gut dysbiosis), the ‘bad’ microorganisms can overpopulate the gut and can cause digestion conditions such as diarrhea, irritable bowel syndrome (IBS), constipation, etc. Consumption of probiotics helps nourish the gut microbiota which could improve these digestive concerns. 

Immunity in the gut

When probiotics are ingested, they reach and colonize your intestines to keep your gut healthy. The GI tract also refers to the human’s largest immune organ, as it comprises up to 70-80% of immune cells (Abbas et al, 2017). The immune system helps to recognize foreign substances that are introduced into the body and provide immune defenses. During food ingestion, immune cells located on the walls of small intestines identify any invading pathogens and toxins within the gut, followed by triggering the formation of antibodies to help fight these harmful substances. The immune system and gut develop a mutualistic relationship to regulate and support each other, it is therefore important to develop a healthy gut that can help to maintain a strong immune system. 

Microbiota and the brain-gut connection

Other than that, there are an estimated 100 million neurons located in the human small intestine that interacts bidirectionally with the brain, in which this interaction is called the gut-brain axis. Therefore, alteration of the gut microbiota may be associated with the pathogenesis of neurological health conditions such as stress, depression, anxiety, etc. (Kim et al., 2018).

On-going research on the benefits of probiotics

The most documented health benefits of probiotics are mainly on digestive health, with some other studies showing a positive effect on health conditions including immunity-boosting, oral health, feminine health, brain-gut axis, etc. On-going research is currently progressing to discover more information regarding other health benefits of probiotics.

Type of probiotics and its effect

There are dozens of probiotics available nowadays, with the two most common groups comprising Lactobacillus and Bifidobacterium species. Each probiotic group includes various species, and each species contain different strains. Other bacteria (e.g. Bacillus and Streptococcus) and a specific yeast (Saccharomyces boulardii) have also been reported to be beneficial probiotics. Though all probiotics provide health benefits, the beneficial effect of each specific strain is determined by their property in the microbiota, therefore different probiotics are used to address different health conditions. For example, a certain probiotic that is used to treat diarrhea may not be or less effective against other infections. Furthermore, the response towards probiotics can vary between individuals due to the difference in the composition of the gut microbiota (Joint Research Centre, EU Commission, 2018).

The most common probiotic types – Lactobacillus and Bifidobacterium

Lactobacillus is naturally found in the gut, with the majority residing in the small intestines whereas, at the outside of the body, it is naturally found in many fermented food (Walter, 2008). In the small intestine, lactobacillus aids in food digestion and protects against harmful bacteria. Lactobacillus is also referred to as lactic acid bacteria (LAB) as it produces lactic acid as the major metabolic end-product by breaking down carbohydrates, such as glucose. The lactic acid produced by LAB lowers the pH in the gut, resulting in an unfavorable environment that inhibits the growth of pathogenic bacteria (Dittoe et al., 2018). Examples of the most common lactobacillus species found in probiotics supplements include lactobacillus acidophilus and lactobacillus rhamnosus, which have been clinically reported to support optimum digestive health. 

Bifidobacterium is primarily located in the large intestine (Shigwedha et al., 2013). The general beneficial effects of these bacteria include fiber digestion, water-soluble vitamin production for body absorption and offer protection against pathogens. These bacteria are also classified as LAB as they metabolize sugar to produce lactic acid, as well as acetic acid. Examples of the most popular Bifidobacterium species are Bifidobacterium longum and Bifidobacterium bidifium.

Prebiotics as food source of probiotics

Apart from including probiotics in our diet for a healthy gut, it is also important to incorporate prebiotics as they act as food source for these friendly bacteria. Prebiotics are defined as ‘a selectively fermented compound that result in specific changes in the composition and/or activity of the gut microbiota, therefore conferring beneficial health effects on the host’ (Carlson et al., 2018). Prebiotics are naturally occurring non-digestible fiber that can be found in many food sources including chicory root, bananas, asparagus, leek, etc. Prebiotic is also now extensively available in several forms of dietary supplements including powder, liquid and capsule. The common types of prebiotics include fructooligosaccharides (FOS), inulin, galactooligosaccharides (GOS).

Health impact of prebiotics in human

As prebiotics can promote the growth of gut microflora, this can help in restoring the gut microflora composition, resulting in amelioration or prevention of many chronic inflammation-related disorders that are closely linked to gut dysbiosis. The fermentation of prebiotics by gut microbiota results in the formation of short-chain fatty acid (SCFA), a key mediator for gut health effects. In addition, the production of SCFAs has led to the elicitation of other beneficial physiological effects, including immune system potentiation, reduction in gut pathogenic bacteria population, enhance mineral absorption that could link to a decreased risk of osteoporosis, etc. Studies have also shown that the addition of prebiotics help alleviates symptoms of inflammatory bowel diseases (IBD) and improve other digestive-related concerns.

Synergistic effect of prebiotics and probiotics

Prebiotics, when taken in combination with the appropriate strains may provide a synergistic effect on overall health, especially gut health. Apart from solely supplying food sources to the indigenous gut microbiota, it is also advisable to introduce additional probiotics into our diet for better health effects.  


  1. WHO, 2011, http://www.fao.org/3/a-a0512e.pdf
  2. K. Abbas, A. H. H. Lichtman, S. Pillai, Cellular and Molecular Immunology E-Book, Elsevier Health Sciences, 2017.
  3. Sender et al., 2016, https://sci-hub.ren/10.1371/journal.pbio.1002533
  4. Shreiner et al., 2015, https://sci-hub.ren/10.1097/MOG.0000000000000139
  5. Kim et al., 2018, https://sci-hub.ren/10.1007/s12275-018-8032-4
  6. Walter, 2008, https://sci-hub.ren/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2519286/
  7. Dittoe et al., 2018, https://sci-hub.ren/https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6136276/?report=reader#B63
  8. Joint Research Centre, EU Comission, 2018, https://publications.jrc.ec.europa.eu/repository/bitstream/JRC112042/human_gut_microbiota_online.pdf
  9. Shigwedha et al., 2013, sci-hub.ren/10.5772/50457
  10. Carlson et al., 2018. https://bit.ly/3bsNodW