Do "probiotics" have health benefits?

Question

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?

Answer 1

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 the article Probiotic drinks do not aid health, Europe says:

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.

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.

Answer 2

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.

Answer 3

It might help your mood. Recent mouse research showed an effect: Ingestion of Lactobacillus strain regulates emotional behavior and central GABA receptor expression in a mouse via the vagus nerve.

Answer 4

There has been an article about probiotics 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.

Answer 5

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

Meta-analysis of probiotics for the treatment of irritable bowel syndrome:

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.

A systematic review and meta-analysis: probiotics in the treatment of irritable bowel syndrome:

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.

Efficacy of probiotics in irritable bowel syndrome: a meta-analysis of randomized, controlled trials:

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

Meta-analysis: the effects of Saccharomyces boulardii supplementation on Helicobacter pylori eradication rates and side effects during treatment:

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.

Meta-analysis: Lactobacillus containing quadruple therapy versus standard triple first-line therapy for Helicobacter pylori eradication:

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.

Meta-analysis: the effects of gut flora modulation using prebiotics, probiotics and synbiotics on minimal hepatic encephalopathy:

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.

Influence of consumption of probiotics on the plasma lipid profile: a meta-analysis of randomised controlled trials:

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.

Effect of Bifidobacterium animalis subsp lactis supplementation in preterm infants: a systematic review of randomized controlled trials:

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

Updated Meta-analysis of Probiotics for Preventing Necrotizing Enterocolitis in Preterm Neonates:

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.

Answer 6

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 separate 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 significant 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.