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Probiotics are officially defined as:
Oral probiotics are living micro-organisms which, upon digestion in certain numbers, exert health benefits beyond inherent basic nutrition.

A more common definition is:
A probiotic is a live microbial feed supplement which beneficially affects the host by improving its intestinal microbial balance

The word ‘probiotic' is derived from the Greek words for ‘Pro Life' and has been defined in many different ways during the last decades. In all cases, however, it designated a bacterial product, which would benefit the health of the host.

The three main aspects of the definition are:

  • the micro-organisms (bacteria) are alive
  • the bacteria are administered orally
  • the bacteria should be capable of reaching the intestine alive, in order to have an influence on the microbial balance

This means that probiotic bacteria should be resistant against acid (stomach), bile, capable of growing under anaerobic conditions and be non-toxic. These criteria limit the number of bacterial species and strains to the following groups of bacteria: Lactobacillus, Streptococcus and Bifidobacterium species, although some other species can be used in some cases (such as yeasts and Bacillus species in animal nutrition). All three genera are part of the lactic acid bacteria and are naturally present in the intestine as well as in many fermented (mainly acid) dairy products.



Probiotic bacteria are very strain dependent, not species dependent. A strain is a type of a bacterial species, similar as to the example below :

Bacterial group = German car = lactic acid bacteria
Bacterial genus = Volkswagen = Lactobacillus
Bacterial species = VW Golf = Lactobacillus acidophilus
Bacterial strain = VW Golf 1.4 D = Lb. acidophilus LC1

Everybody knows that a Volkswagen Golf 1,4 D has other characteristics than a Volkswagen Golf 2.0i turbo, but you can't see the difference on the outside.

The same is true for bacteria; they all look the same, but the biological characteristics (‘the engine') are different. Hence, claims on health effects of a certain probiotic are only valid for that specific strain, not species.

See also the part on ‘joyriding‘ below.


Traditional probiotic products are acid fermented dairy products, similar to yoghurts. The traditional yoghurt bacteria (Lactobacillus delbrueckii ssp bulgaricus and Streptococcus salivarius ssp thermophilus ) are not considered probiotics, and yoghurt therefore is not a probiotic product, unless other, probiotic, species have been added.

Probiotics are claimed to have beneficial effects on the host (human or animal) health. The following claims have been attributed to strains of lactobacilli and bifidobacteria:

  • inhibition of potential pathogens, such as E. coli or Clostridium perfringens
  • prevention of diarrhoea caused by (rota)virus or Salmonella
  • reducing the effects of a Candida infection
  • positive effects on cholesterol level
  • prevention and/or reduction of colon cancer
  • stimulation of the immune system
  • production of vitamins
  • increased defecation and reduced constipation
  • improving the uptake of minerals, especially calcium
  • digestion of lactose for lactose-intolerant persons

However, most of these claims are very vague and in most cases not proven scientifically. Only a few proper scientific studies with normal adult volunteers have been carried out, and only for a few strains. For only a few strains some of the above claims have been verified. Reduction of diarrhoea, improved digestion of lactose, reduced constipation and beneficial effects on Candida have been scientifically proven for a number of strains. For most other claims there is no or very little scientific evidence.

For each individual strain (and product) the claims should be properly investigated, which, unfortunately, has not been done for many probiotics and probiotic products, especially the lyophilised powders, pills and capsules (food supplements).

Even if there is scientific proof that a certain strain has probiotic characteristics, it does not mean that the strain is effective in every person, as each person has his/her own intestinal flora, which may limit the effectiveness of a probiotic product.

Whether probiotic products are effective is therefore very hard to predict. There are many products on the market which are most likely not effective at all. Two recent studies, in the Netherlands and the UK, have shown that in many products (mainly food supplements) no or very few living bacteria are present, which thus are certainly ineffective. In the Dutch study, 80% of the products showed wrong information on the label. A short own survey of the Wageningen University, showed similar data on label information for non-Dutch products.

The EU (and US) food law describes that all ingredients should be properly listed. However, for many probiotic products this seems not to be the reality. As probiotic effects are strain dependent, as described above, it is necessary to mention the proper bacterial name and strain. As bacterial nomenclature often changes, it is necessary to mention the strain numbers/designation, as these do not change. Only by using the strain number the consumer, or the dietician or physician, can verify the (claimed) effects of the bacteria and thus the product.

If the label shows obsolete or wrong names, it can reasonably be assumed that the producer is not aware of the scientific literature of the last decades.

When in doubt about the product, always ask the producer for the strain numbers and scientific references on the claims. Be aware of advertising and ‘joyriding', see below. Reliable producers can easily provide this information. When the information can not be provided, be sceptical on the product !


Joyriding means that the producer of a probiotic product provides background material on the bacteria or claims, which has been carried out, or dealt with, totally different bacteria.

It is very common that a producer (in most cases of food supplements) provides background information on-line. For example on a product that allegedly contains Lactobacillus casei . In most cases no strain number will be provided. The site provides information and links on Lb. casei in general and other lactic acid bacteria, which gives a very good impression. All this seems logical and in order, but, when translated to cars you get the following:

A garage sells a Volkswagen Golf 2.0 D (the Lb. casei ). In his background information he gives a lot of engine and other details on all types of Volkswagen Golf (other Lb. casei strains), on other Volkswagen cars (other Lactobacillus species) or even on a BMW (bifidobacteria). He thus claims that the Volkswagen Golf 2.0 D is a very good car, because BMW also makes good cars...

Nobody would take this garage seriously, but it is common practice in probiotic food supplements...

The main reason hereof is that most companies can not afford the very expensive (clinical) trials that are necessary to select a strain and verify a claim. As they want to sell their own bacteria they simply use data from other companies. The effectiveness of such products thus is questionable.

As a consumer the following aspects can give an indication on the reliability of a product:

  • are the names correct (both wrong names as fantasy names (such as a Toyota Golf) are used). If in doubt use this site; if the name is not mentioned, the label is incorrect.
  • presence of strain numbers
  • presence of a consumer service (phone, mail)

Old names

When the label states the presence of the following species, the producer is not aware of current scientific data:

Lactobacillus bifidus; this name became obsolete in 1969 (!) and may not be used since. Producers claiming the presence of this ‘species', therefore are not up-to-date. The name was used for what is now the whole genus Bifidobacterium, with 22 different species. The name has as much value as stating that a dairy product contains milk. Or, in the car analogy, the garage states that he sells a German car, which gives no information at all on the type and characteristics.

Streptococcus faecium ; this name became obsolete in the early 1980s and may not be used since. The correct name is Enterococcus faecium. As this species is also a known pathogen, it is necessary that the strain number and name are properly used.

Fantasy names

Fantasy names are names observed on ‘probiotic' products, but that do not exist and thus are illegally used.

Lactobacillus sporogenes ; this name is a fantasy name; no bacterial species with this name exist. It is claimed that this bacterium makes spores. By definition, lactobacilli can not make spores. It is unknown which species is used in the products with this ‘bacterium'. It has been mentioned (by the producer (!)) that it is actually a Bacillus coagulans strain. Click here for more detailed information on this name.

Lactobacillus caucasicus; another fantasy name. It is totally unknown which bacterium is used in products with this ‘strain'.

Any health benefits of products with these two ‘species', are not to be expected. Any literature on these bacteria can not be considered reliable, as no microbiological or medical journal would accept data on a non existing species.

Lactobacillus acidophilus casei . This should be either a Lb. acidophilus, or a Lb. casei . It is like selling a Volkswagen Golf Passat.

Verified probiotic strains:

Below some examples of well defined probiotic bacteria, on which much scientific literature is available. Only strains used in many different countries are mentioned.

Lactobacillus casei Shirota (or LCS), from Yakult and used in the product of the same name.
Lactobacillus rhamnosus LGG, used in over 25 countries. Strain owner is Valio from Finland . Lactobacillus acidophilus LA7, in many dairy products
Lactobacillus acidophilus LA5, in dairy products and food supplements
Lactobacillus acidophilus DDS, mainly in food supplements
Bifidobacterium lactis, BB12, in dairy products
Bifidobacterium longum BB536, in dairy products and supplements
Lactobacillus johnsonii La1(also LC1), used in products from Nestlé
Bifidobacterium animalis DN-173 010 (Bifidus Essentis), used in products by Danone

Verified non-probiotic strains

The following organisms are not probiotic, as they do not survive the stomach and bile and will thus not be alive in the intestine:

The yoghurt bacteria Lactobacillus delbrueckii ssp bulgaricus and Streptococcus salivarius ssp thermophilus, Lactobacillus helveticus

More information

If you are not sure about label information we may be of help. Please mail the detailed label information (preferably a scan) to (please write in English) is an initiative of Stichting Food-Info, The Netherlands

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