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Probiotics: beneficial bacteria for health? by Elisabeth Weichselbaum
by Dr Elisabeth Weichselbaum Nutrition Scientist British Nutrition Foundation
Dr Elisabeth Weichselbaum has worked on a review on probiotics summarising the current evidence on the effects of probiotic microorganisms on human health, focusing on gut-related health and the immune system.
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In the past months and years, probiotics have been a popular topic in the media; some articles describing them as ‘miraculous bugs’, others condemning them as not being effective and even potentially harmful. It is no wonder then, that consumers are getting increasingly confused as to whether probiotics are beneficial for their health or not.
Probiotics are defined as live microorganisms – mostly bacteria – which, when taken in adequate amounts, confer a health benefit. They comprise of a large number of bacteria and other microorganisms such as yeasts.
Microorganisms have been added to foods for centuries to kick off the fermentation process, but most of these do not survive the gut passage well. Probiotics, in contrast, must be able to survive the harsh conditions during their passage through the intestinal tract to be able to influence the human gut microflora. However, they do not become established members of the normal intestinal flora, but generally persist only for the period of consumption and for a relatively short period thereafter.
There are a relatively large number of in vitro animal and human studies on the health effects of probiotic strains. But ‘probiotics’ is an extremely complex topic, which may be one of the reasons for conflicting messages in the media. Speaking about ‘probiotics’ in general may be as misleading as speaking about ‘pills’ and their effects on health – there are many different pills on the market, each targeting a certain aspect of our health; in a similar way, probiotics seem to work in a very strain specific manner. If a certain strain has been found to affect a certain health outcome, such as irritable bowel syndrome (IBS) symptoms, it would be misleading to state that ‘probiotics’ are effective in relieving IBS symptoms. It is important to remember, that each single strain has to be tested for each single health outcome it is referring to.
Increased effectiveness
There is emerging evidence that as well as needing to test specific probiotic strains for their effectiveness, it is also important to investigate whether they are able to deliver health benefits in the vehicle through which they are delivered (e.g. capsules, dairy products etc). A study by Prof Whorwell from the University of Manchester and his team found that the form in which the probiotic is given can considerably impact on its effectiveness (2). They showed that although a dose of 1x10 8 colony forming units (CFU) per ml given in encapsulated form was significantly superior to placebo in reducing several IBS symptoms, no effect could be observed with a higher dose (10 10 CFU). However, in a previous study, they had shown the same dose to be effective if given in a milk product. Further investigation showed that the high dose in a capsule form was resistant to stomach acid and did not dissolve properly, forming a glue-like mass. This probably explained why the higher dose was effective in milk but not in capsule form. Therefore, each single probiotic product should be studied as a whole before being available for purchase.
Another reason for conflicting reports about probiotics is the result of reports that focus on single studies without putting findings into the context of the totality of scientific evidence available. In order to disentangle some of the confusion, the British Nutrition Foundation has recently carried out an in-depth review of the evidence on probiotics and their effects on health (1). Data from human studies showed that for some probiotic strains, such as Lactobacillus rhamnosus GG or Saccharomyces boulardii, good evidence for their effects in certain health outcomes exists. Both strains seem to be effective in preventing antibioticassociated diarrhoea and in alleviating acute diarrhoea in children – although their effect seems to be more pronounced in Western countries.
Reducing symptoms
There is also some evidence that probiotic strains may be able to reduce the occurrence of Clostridium difficile associated disease in hospitalised patients; however, more studies will be needed to confirm these findings. For other strains the evidence available is rather limited, which does not mean that they are not effective, but rather that more studies are needed to determine whether they exert an effect on certain health aspects. There also seems to be big potential of certain probiotic strains in reducing the occurrence of active disease in patients suffering from ulcerative colitis (Escherichia coli Nissle) and pouchitis (VSL#3, a mix of eight different probiotic strains), although studies have failed to show any effects in patients with Crohn’s disease. IBS sufferers have shown a reduction in symptoms when being treated with selected probiotic strains; however, high placebo effects have been reported as well. The evidence of the efficacy of probiotics in patients suffering from constipation is limited. Although results are conflicting, evidence seems promising for some strains to bring relief to patients suffering from constipation.
Studies investigating the preventive effect of probiotics in the context of common cold and flu infections show that the studied strains failed to lower the incidence of episodes, but that they have a potential to decrease the duration of episodes. This suggests that the immune system may be more efficient in fighting off common cold and flu infections with regular probiotic consumption, but more studies are needed to confirm those early findings. The evidence so far does not suggest that probiotics are effective in preventing or treating allergies or in treating eczema. However, some probiotic strains seem to lower the risk of developing eczema if taken by pregnant women and their infants in early life.
Altogether, it is very difficult and misleading to make statements about the general effects of ‘probiotics’ on health. Each probiotic strain and each single product has to be specifically tested for its effectiveness on a certain health outcome. As research around probiotics has – in scientific measures – only begun relatively recently, it is not surprising that the number of large human intervention studies is at the moment rather limited. It will be exciting to see how this field of research will evolve and in a few years we should have a clearer picture of the possible health benefits of different probiotic strains and products.
More detailed information on the health benefits of probiotics can be found in the December 2009 issue of the Nutrition Bulletin (Probiotics and health – a review of the evidence).
References 1 Weichselbaum E (2009) Probiotics and health: a review of the evidence. Nutrition Bulletin 34:340–373. 2 Whorwell PJ, Altringer L, Morel J et al (2006) Efficacy of an encapsulated probiotic Bifidobacterium infantis 35624 in women with irritable bowel syndrome. Am J Gastroenterol 101(7):1581-1590.
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