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Probiotics 101: Everything You Need To Know

Probiotics 101: Everything You Need To Know
Elle Kelly
Registered Dietitian4 months ago
View Elle Kelly's profile

Your gut is home to a collection of living microorganisms (like bacteria and yeast). It is important to maintain a balance of both good and bad bacteria in the gut to support digestive health, but also overall health.

This is where probiotics are incredibly useful.

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What are probiotics?

Probiotics are ‘friendly’, or beneficial, bacteria which can be found in food and supplements.Literally translated as “for life”, probiotics are defined by the World Health Organisation as “live microorganisms which when administered in adequate amounts confer a health benefit on the host” (1).

How do probiotics work?

Probiotics are live bacteria and are intended to reach the gut alive, although the efficacy of different supplements vary. They work to restore and maintain the balance of bacteria within the gut. An imbalance in good and bad bacteria can cause dysbiosis, which is associated with symptoms such as bloating and changes to bowel movements (2, 3).

Probiotics help through a few mechanisms;
  • Inhibiting pathogens (harmful bacteria, viruses and other microorganisms) from sticking to the gut wall (4)
  • Altering the pH balance in the gut, again inhibiting the growth of pathogens (5)
  • Creating a healthy balance of gut bacteria
probiotics explained

Types of probiotics

Each species of probiotic in your gut provides different benefits, so the more diverse our gut microbiome is, the more benefits you can experience.

There are different species of bacteria and types of yeast that make up the three primary probiotics on the market, these are:

  • Bifidobacterium (bacteria)
  • Lactobacillus (bacteria)
  • Saccharomyces boulardii (yeast)

There are many different strains of these primary probiotic species.

When you check out a label on probiotic supplements or foods, you’ll often see names like “L. acidopholus” or “B. breve” which indicate the species (B for bifidobactirum, L for lactobacillus).

These probiotics are often found in foods that have been fermented, and the specific strain of bacteria or yeast might vary. This article talks more about the seven best probiotic foods.

How do I know which type of probiotic I need?

If you’re considering taking a probiotic supplement, speak to your healthcare provider to confirm if they’re suitable for you and your goal.

What is the most effective probiotic?

The most widely investigated probiotics and ones for which health benefits have been established are within the Lactobacillus and Bifidobacterium species, which are commonly added to yoghurt and fermented milk drinks.

Due to the various strains and species of probiotic bacteria available and their potential benefits, no single probiotic has been identified as the best or most effective overall.

Benefits of probiotics

Each type of probiotic works a little differently based on its chemistry, and therefore can provide different benefits, such as:

Supports Digestion

Probiotics can help support the natural balance of bacteria in our gut.

An imbalance in this bacteria can cause dysbiosis, which is associated with symptoms such as bloating and changes to bowel movements (6).

There is some evidence that probiotics can be helpful in some cases of irritable bowel syndrome (IBS) too (7).


As probiotics pass through the body, they attach to the lining of the intestine, and this attachment is thought to prevent pathogenic bacteria, or bad bacteria that can cause illness from attaching itself and therefore infecting us (4).

Specifically, Lactobacillus and Bifidobacterium probiotic species produce different types of acid which can lower the pH balance within the intestine, which inhibits the growth of pathogenic bacteria (5).

Reduced Risk of Metabolic Diseases

Probiotics can influence metabolism, and evidence has shown that they can help to reduce the risk of metabolic diseases such as diabetes and cardiovascular disease.

A randomised control trial found that Lactobacillus gasseri SBT2055 (L.gasseri), a type of probiotic, supported a reduction in abdominal adiposity (8), which is considered a marker for type 2 diabetes, cardiovascular diseases, cancers, and total mortality (9).

Other parameters such as total body fat mass and BMI also significantly decreased, which were not seen within the control group.

When participants stopped taking the supplement, the results were reduced, suggesting that regular consumption may be required.

A review of multiple studies identified that probiotic supplementation in individuals who have metabolic syndrome resulted in improvements of blood pressure, glucose metabolism, and lipid profile in some studies (10).

probiotics explained

Probiotic supplements

The most common reason for people to take a probiotic supplement is to help restore the natural balance in the gut after being ill.

Antibiotics not only target the harmful bacteria causing an infection, but they can impact the levels of the good bacteria in the gut and so taking a probiotic can help to replenish the levels of healthy bacteria in the gut.

Probiotics may also improve conditions such as bowel habits (11), thrush (12) and even mental health (13, 14).

However, probiotic supplements are not the only way to support your gut health - there are also many probiotic foods that are available.

Many of these foods are either fermented (like kimchi or sauerkraut) and others have probiotics added during processing.

Get a full list of the best probiotic foods here.


The 7 Best Probiotic Foods

And how they keep your gut in check.

3 years agoBy Liam Agnew

What’s the difference between probiotic and prebiotic?

Put simply, probiotics are the beneficial bacteria, and prebiotics act as the fertiliser.

Prebiotics are a type of fibre that promotes the growth and colonisation of probiotics.

Prebiotics stimulate the growth of different species of bacteria and consequently have an ability to positively modify our gut microbiota (15) and evidence suggests that the joint use of the probiotics with prebiotics increases the survival, and hence the efficiency, of probiotics (16).

Take home message

Both pro- and prebiotic supplements have been shown to have positive effects on the gut microbiome, general health and even in specific conditions, however, more research is required to clearly identify what probiotic strain is most effective for certain results.

Nonetheless, you can still benefit from including probiotic and prebiotic foods within your diet daily to support the balance of bacteria in your gut.

Speak to your healthcare provider for bespoke information about which probiotic supplement might suit you best.

Want more advice on gut health?


Our articles should be used for informational and educational purposes only and are not intended to be taken as medical advice. If you're concerned, consult a health professional before taking dietary supplements or introducing any major changes to your diet.

  1. FAO/WHO. (2001). Evaluation of health and nutritional properties of powder milk and live lactic acid bacteria. Food and Agriculture Organization of the United Nations and World Health Organization Expert Consultation Report, 1-34.
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  3. 220–230.
  4. Quigley, E. M. (2022). Clinical trials of probiotics in patients with irritable bowel syndrome: some points to consider. Journal of Neurogastroenterology and Motility, 28(2), 204.
  5. Scarpellini, E., Cazzato, A., Lauritano, C., Gabrielli, M., Lupascu, A., Gerardino, L., … & Gasbarrini, A. (2008). Probiotics: which and when?. Digestive Diseases, 26(2), 175-182.
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  9. Quigley, E. M. (2022). Clinical trials of probiotics in patients with irritable bowel syndrome: some points to consider. Journal of Neurogastroenterology and Motility, 28(2), 204.
  10. Kadooka, Y., Sato, M., Imaizumi, K., Ogawa, A., Ikuyama, K., Akai, Y., … & Tsuchida, T. (2010). Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial. European journal of clinical nutrition, 64(6), 636-643.
  11. Gagnon, E., Pelletier, W., Gobeil, É., Bourgault, J., Manikpurage, H. D., Maltais-Payette, I., … & Arsenault, B. J. (2022). Mendelian randomization prioritizes abdominal adiposity as an independent causal factor for liver fat accumulation and cardiometabolic diseases. Communications Medicine, 2(1), 130
  12. Tenorio-Jiménez, C., Martínez-Ramírez, M. J., Gil, Á., & Gómez-Llorente, C. (2020). Effects of Probiotics on Metabolic Syndrome: A Systematic Review of Randomized Clinical Trials. Nutrients, 12(1), 124.
  13. Hempel S, et al. (2012). Probiotics for the prevention and treatment of antibiotic-associated diarrhea: A systematic review and meta-analysis.
  14. Mundula, T., Ricci, F., Barbetta, B., Baccini, M., & Amedei, A. (2019). Effect of Probiotics on Oral Candidiasis: A Systematic Review and Meta-Analysis. Nutrients, 11(10), 2449.
  15. Wang H, Lee IS, Braun C, Enck P. Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. J Neurogastroenterol Motil. 2016;22(4):589-605. doi:10.5056/jnm16018
  16. Mohammadi AA, Jazayeri S, Khosravi-Darani K, et al. The effects of probiotics on mental health and hypothalamic-pituitary-adrenal axis: A randomized, double-blind, placebo-controlled trial in petrochemical workers. Nutr Neurosci. 2016;19(9):387-395. doi:10.1179/1476830515Y.0000000023
  17. Chung, W. S. F., Meijerink, M., Zeuner, B., Holck, J., Louis, P., Meyer, A. S., … & Duncan, S. H. (2017). Prebiotic potential of pectin and pectic oligosaccharides to promote anti-inflammatory commensal bacteria in the human colon. FEMS microbiology ecology, 93(11), fix127.
  18. Mäkeläinen, H., Forssten, S., Saarinen, M., Stowell, J., Rautonen, N., & Ouwehand, A. (2010). Xylo-oligosaccharides enhance the growth of bifidobacteria and Bifidobacterium lactis in a simulated colon model. Beneficial Microbes, 1(1), 81-91.
Elle Kelly
Registered Dietitian
View Elle Kelly's profile
Elle Kelly is a registered dietitian specialising in eating disorders and disordered eating. Elle is also a registered sports dietitian with a MSc in applied sports nutrition, and currently combines her specialities to support recreational to elite level athletes to fuel their performance whilst improving their relationship with food in her own clinic, EK Nutrition. Elle is passionate about providing evidence-based information in a way that is accessible to everyone, and always wants to help filter though the nuance and myths that circulate within the health and fitness industry so that induvials can make informed decisions about their nutrition. Elle is a member of the BDA and HCPC, and regularly undertakes supervision and CPD courses to ensure that she keeps her skills and knowledge up to the highest standard to support her clients. Elle enjoys long distance running and dabbling in cross fit, is a passionate cook and loves to travel and explore new places.