The Earthen Chalice

Florally challenged

The gut microbiome is not unlike a pet that can make your life miserable if you forget to feed it. But instead of meowing, barking or throwing things off of cupboards, an unhappy gut flora has a more subtle influence on your mental and physical health. Enter probiotics, which are marketed as an easy and effective fix for a troubled microbiome. They’re traditionally sold in the form of yoghurts, sugary drinks or pills, and many people are convinced that they work. But the question of whether they really help, or maybe even hurt, is far from answered.

Fig. 1: Natural remedy or just another sugar crash?

What does it do?

Could potentially help balance your gut microbiome and support you during antibiotic treatment. Overall, current results are unclear and there seems to be no definite benefit to taking probiotics.

Are there negative effects?

Side effects are possible but rare in healthy people, and are mostly light gastro-intestinal troubles. In people with certain pre-existing conditions, taking probiotics can lead to infections and even raise the mortality rate.

How much should you take?

General recommendations range from 5-10 billion CFU (colony-forming-units) for children and 10-20 billion CFU for adults per day. This is only a vague reference based on the dosages used in many studies.


Health effects

Certain uncertainty

The general idea of probiotics is a simple one: you take friendly bacteria and send them all the way down to your gut. Once there, they start to multiply and help you digest food and keep bad bacteria away, just like a healthy gut flora should.[1] The idea is over hundred years old and was originally practiced by giving patients fermented milk, also known as sour milk.[2] The modern alternative of fermented milk is called yoghurt, and the secret lies in its sour taste. Yoghurt contains so-called lactic acid bacteria that turn lactose (tasteless) into lactic acid (sour). Such lactic-acid bacteria are also naturally found in the human gut.[3] If eaten with food or taken as a supplement, some of these bacteria will be enriched in the gut for up to multiple days.[4] Many older studies suggest that this can have positive effects in people who suffer from diarrhea during antibiotic therapy, and help those fighting an infection of C. difficile or H. pylori.[5-8] In children delivered via caesarean section, probiotics were found to help prevent allergies.[9] But unfortunately, many recent large-scale reviews, which compare the data of hundreds of studies, have come to the same conclusion: probiotics are promising, but the data is highly conflicting and unreliable. There is no clear trend of a positive effect of antibiotics on health.[10-17]


Side effects

Good bugs, bad bugs

It’s still unclear what exactly lactic acid bacteria do in the gut, and it is unknown how supplementing them can change the total microbiome. It’s possible that taking lactic acid bacteria will suppress other, more useful kinds of bacteria.[18] Recorded side effects of probiotic supplements include infections and digestive troubles.[19] In people suffering from certain diseases that weaken the immune system, probiotics can be outright dangerous.[20, 21] And while traditional lactic acid bacteria have been used safely for decades, taking supplements with new and untested kinds of bacteria can result in unknown side effects.[22, 23] All in all, probiotics are considered to be safe for most people, and side effects are possible, but unlikely.[24]



Colonizing the colon

The dosage of probiotic supplements is usually given as “CFU” or colony-forming-units. This is the number of bacteria in any given product which are able to reproduce. Because only a part of the bacteria we take in reach our gut alive, the CFU is an important value. Studies that found positive effects for probiotics often also noted a difference between low and high CFU numbers, with higher numbers being more effective. An example of a recommended CFU count according to many studies would be 5 to 10 billion CFU per day for children and 10 to 20 billion CFU per day for adults.[25]

These recommendations only make sense if we believe that probiotics have a positive impact on health. Unfortunately, even studies on probiotics for digestive troubles are inconsistent and full of publication bias.[17] Because many of these trials are paid for by supplement companies, negative results are often simply not published.[26] Even authors of studies with positive results mention that the relationship of the probiotic to the already existing microbiome, diet, medications, psychological stress and other factors is unknown.[27] According to the current literature, probiotics are not recommended in disease or health. But all in all, the research is promising, and taking probiotics is probably safe for most people.


Frequently asked questions (FAQ)



  1. Meijer, K., P. de Vos, and M.G. Priebe, Butyrate and other short-chain fatty acids as modulators of immunity: what relevance for health? Current Opinion in Clinical Nutrition & Metabolic Care, 2010. 13(6): p. 715-721.
  2. Vaughan, R., The romantic rationalist a study of Elie Metchnikoff. Medical history, 1965. 9(3): p. 201-215.
  3. Azad, M., et al., Probiotic species in the modulation of gut microbiota: an overview. BioMed research international, 2018. 2018.
  4. Brigidi, P., et al., PCR detection of Bifidobacterium strains and Streptococcus thermophilus in feces of human subjects after oral bacteriotherapy and yogurt consumption. International journal of food microbiology, 2003. 81(3): p. 203-209.
  5. Fooks, L. and G.R. Gibson, Probiotics as modulators of the gut flora. British Journal of Nutrition, 2002. 88(S1): p. s39-s49.
  6. Armuzzi, A., et al., The effect of oral administration of Lactobacillus GG on antibiotic‐associated gastrointestinal side‐effects during Helicobacter pylori eradication therapy. Alimentary pharmacology & therapeutics, 2001. 15(2): p. 163-169.
  7. Lesbros-Pantoflickova, D., I. Corthesy-Theulaz, and A.L. Blum, Helicobacter pylori and probiotics. The Journal of nutrition, 2007. 137(3): p. 812S-818S.
  8. Gotteland, M., O. Brunser, and S. Cruchet, Systematic review: are probiotics useful in controlling gastric colonization by Helicobacter pylori? Alimentary pharmacology & therapeutics, 2006. 23(8): p. 1077-1086.
  9. Kuitunen, M., et al., Probiotics prevent IgE-associated allergy until age 5 years in cesarean-delivered children but not in the total cohort. Journal of Allergy and Clinical Immunology, 2009. 123(2): p. 335-341.
  10. López-Moreno, A., et al., Probiotic Strains and Intervention Total Doses for Modulating Obesity-Related Microbiota Dysbiosis: A Systematic Review and Meta-analysis. Nutrients, 2020. 12(7): p. 1921.
  11. Taylor, A.M. and H.D. Holscher, A review of dietary and microbial connections to depression, anxiety, and stress. Nutritional neuroscience, 2020. 23(3): p. 237-250.
  12. Lewis-Mikhael, A.-M., A. Davoodvandi, and S. Jafarnejad, Effect of Lactobacillusplantarum containing probiotics on blood pressure: A systematic review and meta-analysis. Pharmacological Research, 2020. 153: p. 104663.
  13. Nazari, M., et al., Probiotic consumption and inflammatory markers in athletes: a systematic review and meta-analysis. International Journal of Food Properties, 2020. 23(1): p. 1402-1415.
  14. Jiang, J., et al., Effects of probiotic supplementation on cardiovascular risk factors in hypercholesterolemia: A systematic review and meta-analysis of randomized clinical trial. Journal of Functional Foods, 2020. 74: p. 104177.
  15. Barbosa, R.S. and M.A. Vieira-Coelho, Probiotics and prebiotics: focus on psychiatric disorders–a systematic review. Nutrition Reviews, 2020. 78(6): p. 437-450.
  16. Irwin, C., et al., Effects of probiotics and paraprobiotics on subjective and objective sleep metrics: a systematic review and meta-analysis. European Journal of Clinical Nutrition, 2020: p. 1-14.
  17. Preidis, G.A., et al., AGA technical review on the role of probiotics in the management of gastrointestinal disorders. Gastroenterology, 2020. 159(2): p. 708-738. e4.
  18. Gerritsen, J., et al., Intestinal microbiota in human health and disease: the impact of probiotics. Genes & nutrition, 2011. 6(3): p. 209-240.
  19. Boyle, R.J., et al., Probiotics for treating eczema. Cochrane Database of Systematic Reviews, 2008(4).
  20. Didari, T., et al., A systematic review of the safety of probiotics. Expert opinion on drug safety, 2014. 13(2): p. 227-239.
  21. Besselink, M.G., et al., Probiotic prophylaxis in predicted severe acute pancreatitis: a randomised, double-blind, placebo-controlled trial. The Lancet, 2008. 371(9613): p. 651-659.
  22. Donohue, D. and S. Salminen, Safety of probiotic bacteria. Asia pacific journal of clinical nutrition, 1996. 5: p. 25-28.
  23. Marteau, P., Safety aspects of probiotic products. Näringsforskning, 2001. 45(1): p. 22-24.
  24. Snydman, D.R., The safety of probiotics. Clinical infectious diseases, 2008. 46(Supplement_2): p. S104-S111.
  25. Kligler, B. and A. Cohrssen, Probiotics. American family physician, 2008. 78(9): p. 1073-1078.
  26. Million, M. and D. Raoult, Publication biases in probiotics. European journal of epidemiology, 2012. 27(11): p. 885.
  27. Lescheid, D.W., Probiotics as regulators of inflammation: A review. Functional foods in health and disease, 2014. 4(7): p. 299-311.