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One of the only things that natural-food aficionados and food products mega-corporations agree on is that "probiotics" are good for you. I'm wondering if there is any reliable evidence to support the claims that consuming food or supplements with live cultures such as Lactobacillus will result in health benefits.

An example is this claim made by Dannon/Danone:

Consuming certain probiotics can help strengthen the body's natural defenses by providing a regular source of “friendly”bacteria to the intestinal tract, helping to correct an imbalance of the intestinal microflora and optimizing the functioning of the digestive tract’s immune system and intestinal lining.

The range of claims is quite wide - others have have made claims about improving digestion, clearing up acne, and even curing autism. I will keep this question focused on just the one claim:

Is there any reliable scientific evidence that consuming probiotics can improve the immune system?

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Honestly, I'm surprised this question hadn'talready been aked. –  Monkey Tuesday Sep 16 '11 at 5:11
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@MonkeyTuesday: There are a lot of questions to still be asked. Since I went back to university, I hear an absurd amount of common claims that would make good Skeptics questions if I remembered them by the time I was back home. I may have to write them down. –  Borror0 Sep 16 '11 at 5:29
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It's not that I fear we're running out of claims, I was just almost certain this one was already on here. –  Monkey Tuesday Sep 16 '11 at 9:17
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@Monkey Tuesday: Given how heavily this is advertised, I wonder if this could be a sign that the rest of us aren't being skeptical enough? Dare I call this "food for thought?" ;-) –  Randolf Richardson Sep 16 '11 at 21:50
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@Randolf, +1 for the best pun I've heard all day! –  Jonathan Sep 16 '11 at 23:07
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6 Answers

up vote 32 down vote accepted

It depends on what you define as probiotics. If you are referring to the "food products mega-corporations" as you call them, the answer is most likely No, and arguments are given below. This does not mean that there are no real probiotics which have an actual effect on specific health issues. The answer of mmr gives a few examples.

But again to the claims of these mega-corporations: the European Food Safety authority has researched 800 health claims of such companies, and they could not find relationships.

If you prefer easy reading you may like this article: http://www.telegraph.co.uk/health/healthnews/8074182/Probiotic-drinks-do-not-aid-health-Europe-says.html

Products such as Yakult, which are sold at a premium over standard yogurts, cannot be proved to either boost the immune system or aid digestive health, it has been ruled.

The European Food Safety Authority (EFSA) has examined more than 800 health claims from food companies, including those submitted by the multi-billion pound probiotic industry.

EFSA's independent panel of scientists found that the claims that these products could strengthen the body's defences, improve immune function and reduce gut problems were either so general as to be inadmissible, or could not be shown to have the claimed effect.

In a separate ruling, the panel examined a dossier of 12 studies submitted by Yakult for its own strain of probiotic bacteria, Lactobacillus casei shirota. It found that all were inadequate to support the company's claim that its products maintained immune defences against the common cold.

EFSA's ruling is being challenged by the industry, but if these appeals fail the companies will no longer be allowed to market the foods as aiding digestion or helping the immune system in future.

More info on the EFSA's own site: http://www.efsa.europa.eu/en/efsajournal/pub/1767.htm or the report: http://www.efsa.europa.eu/en/efsajournal/doc/1767.pdf

Excerpts from the conclusions:

Claim: “Healthy and balanced digestive system” (ID 1371, 4228)

  • The claimed effects are “intestinal flora”, “digestive health” and “ingestion of cheese containing probiotic culture Lb. paracasei NFBC 338 positively influences the healthy balance of the gut microflora”. The target population is assumed to be the general population. In the context of the proposed wording, it is assumed that the claimed effects refer to maintenance or contribution to a healthy and balanced digestive system.

  • The claimed effects are general and non-specific and do not refer to any specific health claim as required by Regulation (EC) No 1924/2006.

Claim: Increasing numbers of gastro-intestinal microorganisms (ID 864, 1371, 3073, 4228)

  • The claimed effects are “gut health”, “intestinal flora”, “digestive health” and “ingestion of cheese containing probiotic culture Lb. paracasei NFBC 338 positively influences the healthy balance of the gut microflora”. The target population is assumed to be the general population.

  • The evidence provided does not establish that increasing numbers of gastro-intestinal microorganisms is a beneficial physiological effect. A cause and effect relationship has not been established between the consumption of the food(s)/food constituent(s) evaluated in this opinion and a beneficial physiological effect related to increasing numbers of gastro-intestinal microorganisms.

Claim: Decreasing potentially pathogenic gastro-intestinal microorganisms (ID 864, 1371, 3073, 4228)

  • The claimed effects are “gut health”, “intestinal flora”, “digestive health” and “ingestion of cheese containing probiotic culture Lb. paracasei NFBC 338 positively influences the healthy balance of the gut microflora”. The target population is assumed to be the general population. Decreasing potentially pathogenic gastro-intestinal microorganisms might be a beneficial physiological effect.

  • A cause and effect relationship has not been established between the consumption of the food(s)/food constituent(s) evaluated in this opinion and decreasing potentially pathogenic gastro-intestinal microorganisms.

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Thanks for the definitive answer! –  Jonathan Sep 16 '11 at 17:20
    
I've been fooled! Good thing I never cared enough about my health to buy this crap anyway. –  Alain Sep 22 '11 at 17:55
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Interesting answer, but these findings are specifically limited to 'products such as Yakut' and 12 studies related to this product, not to probiotics in general. –  David Oct 5 '11 at 3:15
    
@David: this is correct. One of the other answers given by mmr gives some proofs that probiotics can indeed be useful. He certainly deserves more upvotes! But then we are looking at other products than the typical ones from danone cited in the question, with much more specific claims. –  johanvdw Oct 5 '11 at 10:11
    
@johanvdv good point, but danone is provided just as an example, although the question is about probiotics in general. I think it would be helpful if you clarified this point in the beginning of your answer. –  David Oct 5 '11 at 14:25
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Well, all respect to the EFSA, but there are several claims about probiotics that can be found in about five minutes on scholar.google.com that show clear health benefits, not least of which appear to be increased resistance to salmonella infections and improved skin condition in children with dermatitis.

Namely:

The role of probiotic cultures in the control of gastrointestinal health, the Journal of Nutrition, 2000. Choice quote from the abstract:

There is a relatively large volume of literature that supports the use of probiotics to prevent or treat intestinal disorders. However, the scientific basis of probiotic use has been firmly established only recently...Probiotics represent an exciting prophylactic and therapeutic advance, although additional investigations must be undertaken before their role in intestinal health can be delineated clearly.

Probiotic Bacteria Enhance Murine and Human Intestinal Epithelial Barrier Function, Gastroenterology, 2001. Choice quote:

In vitro studies showed that epithelial barrier function and resistance to Salmonella invasion could be enhanced by exposure to a proteinaceous soluble factor secreted by the bacteria found in the VSL#3 compound.

Effect of probiotic Lactobacillus strains in children with atopic dermatitis, Journal of Allergy and Clinical Immunology, 2003. Choice quote:

A combination of L rhamnosus 19070-2 and L reuteri DSM 122460 was beneficial in the management of AD. The effect was more pronounced in patients with a positive skin prick test response and increased IgE levels.

Now, here's the rub: Do Dannon, Yakult, or any of these other companies provide these bacteria? That I don't know, but the idea that probiotics themselves do nothing has been shown to be wrong.

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A few comments: the EFSA talks about 'the general population'. This certainly does not exclude that for specific groups (like children with atopic dermatitis) probiotics may work. If I had a bad case of Diarrhea and/or use antibiotics (I sometimes work in rural africa, so I know what I'm talking about) I take probiotic medicines (on prescription). Apart from that: the EFSA also talks about probiotics present in specific products, and shows that those have no measurable or proved effect. –  johanvdw Sep 23 '11 at 8:17
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@johanvdw-- I agree with everything you're saying, and there are actual studies underway (or perhaps completed now) about the use of probiotics for diarrhea as a general treatment (journals.lww.com/jcge/Abstract/2006/03000/…). The final question was "Is there any reliable scientific evidence that consuming probiotics can improve the immune system?", and the answer to that is yes. If the question were "does supermarket yogurt provide these same benefits?" The answer is probably 'no'. –  mmr Sep 23 '11 at 20:30
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It might help your mood. Recent mouse research showed an effect: http://dx.doi.org/10.1073/pnas.1102999108 (Should I link directly to the journal the study is in, or is the university press release good enough? Not sure if the journal is publicly accessible, but it's mentioned in the press release.)

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Wow- good find! As my specific question was related to the immune system claims that are found in marketing materials, I can't take this as the actual answer, but I think it's a great find and I really appreciate it. –  Jonathan Sep 22 '11 at 18:32
    
@Jonathan, no-- your question asks "Is there any reliable scientific evidence that consuming probiotics can improve the immune system?", which does not contain a specific marketing claim, but a more general question about the immune system. –  mmr Sep 22 '11 at 21:35
    
You are correct of course, mmr, but that doesn't change that Chuk's answer is about mood nor that the inspiration for my question was marketing claims. –  Jonathan Sep 22 '11 at 22:39
    
@Jonathan-- may I humbly suggest an edit of your question, then? Because I think I've found several positive benefits of probiotics in scientific, peer-reviewed literature. Just not whether or not these companies provide similar results. Maybe something like "Do consumer yogurts provide any scientifically proven benefits via probiotics?" –  mmr Sep 23 '11 at 1:58
    
Sorry, I was looking at the top-level question ("health benefits") instead of focusing on the later change to "immune system". –  Chuk Sep 27 '11 at 19:09
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There has been an article about pro-biotics on sciencebasedmedicine.org, that was (quite surprisingly given the sites record) cautiously positive. The article contains references for most if not all claims it does make.

Scott Gavura concludes

There’s reasonably good evidence that probiotics, when taken with antibiotics, will reduce the risk of antibiotic-associated diarrhea. There is still much to be learned about how these products can be used most effectively, which means it’s unlikely we will see routine use recommended for some time. However, the reassuring lack of side effects, and potential to reduce potentially serious complications of antibiotic treatment, suggests that probiotics may become a valuable addition to antibiotic therapy.

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Numerous meta-analyses show various benefits in addition to the effects on digestive health and diarrhea that were posted before.

http://www.ncbi.nlm.nih.gov/pubmed/18461650

While our analyses suggest that probiotic use may be associated with improvement in IBS methodological limitations of contributing studies. Probiotics warrant further study as a potential therapy for IBS.

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0027769/

Probiotics may have a role in alleviating some of the symptoms of IBS, a condition for which currently evidence of efficacy of drug therapies is weak. However, as IBS is a condition that is chronic and usually intermittent longer term trials are recommended. Such research should focus on the type, optimal dose of probiotics and the subgroups of patients who are likely to benefit the most.

http://www.ncbi.nlm.nih.gov/pubmed/18465170

Probiotics may improve symptoms of irritable bowel syndrome and can be used as supplement to standard therapy.

http://www.ncbi.nlm.nih.gov/pubmed/21039671

In patients with H. pylori infection, there is evidence to recommend the use of S. boulardii along with standard triple therapy as an option for increasing the eradication rates and decreasing overall therapy-related side effects, particularly diarrhoea.

http://www.ncbi.nlm.nih.gov/pubmed/19751434

Our review suggests that supplementation with Lactobacilli could be effective in increasing eradication rates of anti-H. pylori therapy for first-treated patients. Furthermore, Lactobacilli showed a positive impact on some H. pylori therapy-related side effects.

http://www.ncbi.nlm.nih.gov/pubmed/21251030

The use of prebiotics, probiotics and synbiotics was associated with significant improvement in minimal hepatic encephalopathy. Among individual agents, lactulose appears to have the most beneficial effect, followed closely by probiotics and synbiotics.

http://www.ncbi.nlm.nih.gov/pubmed/21930366

These results indicate that a diet rich in probiotics decreases total cholesterol and LDL cholesterol concentration in plasma for participants with high, borderline high and normal cholesterol levels.

http://www.ncbi.nlm.nih.gov/pubmed/20543719

Evidence regarding the potential beneficial effects of B lactis supplementation in preterm infants is encouraging. Further studies to assess clinically relevant outcomes are needed

http://pediatrics.aappublications.org/content/125/5/921

The results confirm the significant benefits of probiotic supplements in reducing death and disease in preterm neonates. The dramatic effect sizes, tight confidence intervals, extremely low P values, and overall evidence indicate that additional placebo-controlled trials are unnecessary if a suitable probiotic product is available.

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In terms of the probiotic Yakult, which has "6.5 billion healthy bacteria in every serve" there was a 2010 review conducted by the European Food Safety Authority. This was a seperate study called to support those made on intestinal health claims (which have been covered by Johan already).

The EFSA panel concluded that a cause and effect relationship had not been established between the consumption of the Lactobacillus casei strain Shirota and maintenance of the upper respiratory tract defence against pathogens by maintaining immune defences. This shouldn't be that surprising considering that 6.5 billion bacteria is 0.0065% of the 100 trillion or so bacteria in the intestines.

The food constituent, Lactobacillus casei strain Shirota, which is the subject of the health claim, is sufficiently characterised. The Panel considers that maintenance of the upper respiratory tract defence against pathogens by maintaining immune defences is a beneficial physiological effect. The applicant identified a total of 12 references as being pertinent to the health claim. These included nine human intervention trials and three animal studies. In weighing the evidence, the Panel took into account that there was no human study from which conclusions could be drawn for an effect of Lactobacillus casei strain Shirota consumption on upper respiratory tract infections, that one human study did not support an effect of Lactobacillus casei strain Shirota consumption on the immune response to influenza vaccination, and that there was a lack of evidence for an effect of Lactobacillus casei strain Shirota consumption on the immune system that could relate to the defence of the upper respiratory tract against pathogens.

Yakult is supposedly backed by a signficant body of science. The number of scientific papers is certainly large, however, most of them are related to in vitro and in vivo experiments, with some human clinical trials done on cohorts (e.g. 1, 2, 3). The trials also tended to use much larger daily consumptions of bacteria, in the order of 40–100 billions of probiotic L. casei Shirota (sorry, links are now behind a paywall in the UK), far above the single bottle concentration of approximately 6.5 billion.

An example of the studies performed shows that the claims are borderline, with both placebo and Yakult treated constipation groups showing improvements (improved constipation 56% vs. 89%, p=0.003) in the second week, or the claims are based on small sample sizes (n=20). This shows why the EFSA concluded as they did.

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