Monday 25 March 2013

Good bacteria...

You can’t move at the moment for adverts for products containing bacteria said to benefit your health in all sorts of ways. Since they are the subject of my PhD, I thought I would try to explain what they are, how they work, and how they can benefit your health.

The World Health Organisation’s definition of probiotics is “live organisms, which when administered in sufficient amounts, can have a beneficial effect on the host’s health.” 1 Essentially this means they are bacteria from groups including lactobacillus, bifidobacterium and lactococcus which you eat, usually in the form of yoghurts containing live bacteria, or freeze-dried in capsules, useful if you’re on a dairy-free diet. With the latter type, the bacteria are effectively in suspended animation inside their capsule. Once the capsule is dissolved by your stomach acid, the bacteria find all the nutrients they need inside your body and come back to life. Once inside you, these bacteria colonise your gut. As a note of caution, these are not to be confused with PREbiotics. Prebiotics are indigestible carbohydrates which can be broken down by your gut bacteria. They are taken with a view to fortifying your existing gut flora. So, simply put:
·         PRObiotics – bugs
·         PREbiotics – bug food

There are several proposed ways in which they work:
·         Prevention of infection, by competing with harmful bacteria (pathogens)  for nutrients;
·         Interaction with your immune system, so that you produce different chemicals (cytokines) which help prevent or improve different conditions;2
·         Prevention of pathogens (such as those that cause food poisoning) from entering your system – the probiotics occupy the sites on the intestinal wall which the harmful bacteria might otherwise use to enter your cells;3
·         Production of antimicrobial compounds such as organic acids, which can prevent the growth and reproduction of pathogens in your system.4
The other great benefit of probiotics is that of improved absorption of nutrients. Gut bacteria are an essential part of your digestion and absorption system, so it makes sense to fortify them so you get the most out of your diet, while preventing all sorts of other illnesses.

There is ever-increasing evidence that probiotics have a number of health benefits. These include reduction of the incidence and duration of colds5, prevention of travellers’ diarrhoea6 and urinary tract infections7 and improvement of inflammatory conditions such as atopic dermatitis.8

It appears the best probiotic strain to take for each health endpoint (be it prevention of certain types of infection, or improving certain chronic conditions) is different. Most recent research – including the research I did for my PhD - suggests that using a probiotic which includes several strains can have an equal, or sometimes greater, effect against several endpoints7,9 suggesting that for overall health, a multi-strain probiotic might give you a greater health effect for your money. (By the way, if you want the full versions of my papers, just shoot me an email to

So that is a very brief introduction to probiotics. Essentially, by taking them you will enhance the good work that the trillions of bacteria already in your gut carry out without you ever noticing. I hope this is useful. If you have any questions, please post them as comments below or contact me at


1          Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria. Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria". Food and Agriculture Organization of the United Nations, World Health Organization. . (2001).
2          Dong, H., Rowland, I., Tuohy, K. M., Thomas, L. & Yaqoob, P. Selective Effects of Lactobacillus casei Shirota on T cell activation, natural killer cell activity and cytokine production. Clinical and Experimental Immunology 161, 378-388 (2010).
3          Gibson, G. R., McCartney, A. L. & Rastall, R. A. Prebiotics and resistance to gastrointestinal infections. Br J Nutr 93 Suppl 1, S31-34, doi:S0007114505000772 [pii] (2005).
4          Tejero-Sarinena, S., Barlow, J., Costabile, A., Gibson, G. R. & Rowland, I. In vitro evaluation of the antimicrobial activity of a range of probiotics against pathogens: Evidence for the effects of organic acids. Anaerobe, doi:S1075-9964(12)00112-6 [pii]10.1016/j.anaerobe.2012.08.004 (2012).
5          Winkler, P., de Vrese, M., Laue, C. & Schrezenmeir, J. Effect of a dietary supplement containing probiotic bacteria plus vitamins and minerals on common cold infections and cellular immune parameters. Int J Clin Pharmacol Ther 43, 318-326 (2005).
6          Gotz, V., Romankiewicz, J. A., Moss, J. & Murray, H. W. Prophylaxis against ampicillin-associated diarrhea with a lactobacillus preparation. Am J Hosp Pharm 36, 754-757 (1979).
7          Chapman, C. M., Gibson, G. R., Todd, S. & Rowland, I. Comparative in vitro inhibition of urinary tract pathogens by single- and multi-strain probiotics. Eur J Nutr, doi:10.1007/s00394-013-0501-2 (2013).
8          Viljanen, M. et al. Probiotics in the treatment of atopic eczema/dermatitis syndrome in infants: a double-blind placebo-controlled trial. Allergy 60, 494-500, doi:ALL514 [pii]  10.1111/j.1398-9995.2004.00514.x (2005).
9          Chapman, C. M., Gibson, G. R. & Rowland, I. In vitro evaluation of single- and multi-strain probiotics: Inter-species inhibition between probiotic strains, and inhibition of pathogens. Anaerobe 18, 405-413, doi:S1075-9964(12)00091-1 [pii] 10.1016/j.anaerobe.2012.05.004 (2012).


  1. Thanks Chris, it's interesting to know there is some science behind the friendly bacteria. Before I read this I thought it was all just marketing BS.

    1. Thanks for looking, Tom.
      There is so much marketing nonsense around, especially with nutrition. Once of my aims with this blog is to clarify some of this, so if there's anything you want to know about, let me know.