What are probiotics or “friendly bacteria”?

According to the World Health Organization (WHO) probiotics are “live microorganisms which when administered in adequate amounts confer a health benefit on the host”. (1)

Thus, we can see that these so-called “friendly bacteria” consist not only of bacteria but of other microorganisms too, such as yeast. (2)

Probiotics are thought to work by increasing the number of beneficial microorganisms in a person’s intestinal system and decreasing the number of potentially detrimental microorganisms. (6)

Where are probiotics found?

In addition to yogurts, probiotics are also found in dietary supplements, such as tablets and powders, as well as suppositories and creams. (3)

Are “live cultures” the same as probiotics?

In short: no. The National Yogurt Association developed the term “live and active cultures”. They use this term to define yogurts that contain the organisms Lactobacillus bulgaricusand Streptococcus thermophiles. These are the organisms used in the fermentation process which they say gives yogurt its “healthful attributes”. (4, 5)

Despite these “healthful attributes”, it is possible that yogurts labeled as containing “live and active cultures”, do not meet the requirements of the definition of probiotics. That is, they may not contain sufficient amounts of live microorganisms to bestow a health benefit on the consumer. (4)

Does the body already contain “friendly bacteria”?

The body does already contain “friendly” bacteria. In fact, most of the bacteria in our bodies are not harmful. (4)

Given that the number of microorganisms in a healthy adult is thought to be many more than the number of human cells themselves (estimates suggest a ratio of 10:1 microorganisms : human cells), it follows that the body not only contains “friendly” bacteria, but it contains lots of them. (3)

Specifically, there are over 100 trillion bacteria within our intestines. These weigh just over 3 pounds (around 1.5kg). (7)

What potential benefits are there of eating probiotic yogurts?

Several potential benefits have been proposed of eating probiotic yogurts. These include:

• treating diarrhea – both the infectious kind and that which occurs as a result of the use of antibiotics
• reducing the symptoms of conditions such as irritable bowel syndrome (IBS) and inflammatory bowel syndrome, such as Crohn’s disease and ulcerative colitis
• decreasing lactose intolerance
• decreasing the risk of particular cancers, particularly colon cancer
• reducing the symptoms of some allergies
• lowering cholesterol levels
• reducing blood pressure
• reducing the risk of some intestinal infections
• treating oral health problems such as gingivitis and periodontitis and preventing tooth decay and preventing colds
• preventing atopic eczema, also known as atopic dermatitis
• treating and preventing hepatic encephalopathy
• curing vaginal infections and also candidiasis and urinary tract infections
• treating constipation
• treating rheumatoid arthritis (3, 4, 6, 7)

Despite these numerous potential benefits of probiotics, further research is needed to provide strong scientific evidence to support these uses. (3, 4)

Moreover, of the research that has been done, little has been in humans. A large part of probiotic research has been on animal models. (6)

Furthermore, the health claims for probiotics have not been approved by the U.S. Food and Drug Administration (FDA). (3)

How do probiotics survive the harsh acidic environment of the stomach?

The pH of the stomach tends to be between 1.8 and 3.5. This means it is very acidic. The acidic nature of the stomach destroys bacteria that may enter the stomach in food. (8)

If the stomach acid kills bacteria, then how do friendly bacteria, or probiotics, survive?

Whether the probiotics survive the harsh environment of the stomach may depend on the type of bacteria they contain. Some bacteria do live naturally in the stomach; therefore certain types of bacteria may survive the acidic conditions. (7)

There have been concerns over the types of bacteria in some probiotics and whether they do actually survive the stomach conditions. In Japan, there are many probiotics based on spore-forming bacteria. This is because the spores may be able to survive in the stomach until they reach the small intestines, which are less acidic. (9, 10)

It is also thought that dairy products, such as yogurts, may buffer the pH of the stomach, which may allow the bacteria to survive. (11)

Does the need for probiotic yogurts vary from person to person?

Although there are currently questions over the potential benefits of probiotics, there is some scientific evidence that shows that probiotic yogurts may be useful for people suffering from antibiotic associated diarrhea (AAD). (12)

AAD is diarrhea that occurs as a side effect of antibiotic use. It is thought to affect around a third of people that take antibiotics. AAD can have symptoms that range from mild to severe. (13)

A paper, published in the Journal of the American Medical Association (JAMA), stated that AAD could be reduced by probiotics. The authors of the study did, however, state that further research is necessary, to show:

• which specific probiotics are most efficient in having this effect
• which type of AAD patients probiotics would benefit and what types of antibiotics these patients take (13)

This research shows that the need for probiotics may depend on the person’s situation. It may be advisable for those that are prone to AAD to try probiotics. However, clearly further research is needed to determine which specific probiotics should be tried and who precisely should try them. (12, 13)

Are probiotics safe?

Probiotics rarely cause serious side effects; however, concerns have been raised over certain probiotic ingestion in immunosuppressed patients. (6)

It has also been suggested that the safety of the different types of probiotics should be considered separately, along with the administration methods. (6)

According to the University Health Services, University of California, Berkeley, the following specific probiotics have been deemed safe for those who are generally healthy:-

• Lactobacillus
• Bifidobacterium
• Saccharomyces boulardi

However, it is recommended that the young, the elderly and those with compromised immune systems should seek advice from a healthcare provider before using probiotics. (14)