Probiotics: what lies behind this name?

“What is a name? What we call ‘rose’ even by any other name would have its scent.” So speaks Juliet to her beloved Romeo in Shakespeare’s play, emphasizing how their love would not stop because of the two rival families’ names. Yet, there are instances when a name can make a difference.

Among areas of recent scientific, medical and commercial interest, few have raised as much controversy as probiotics. Each article published on the subject uses a different definition of probiotic, or criticizes the commonly accepted definition or proposes a new nuance of meaning.

The situation became even more tense in 2006, whenEFSA, the European Food Safety Authority, restricted the use of the word “probiotic” on product labels [1]. Why are probiotics such a hot topic? What is wrong with their definition? To try to answer these questions, we need to take a step back in time.

Probiotics: when and how were they discovered?

We are in Paris at the beginning of the twentieth century. We are in one of the laboratories of theInstitut Pasteur, a center of excellence for microbiological, medical and immunological research. A stern-looking gentleman with a thick dark beard is intent on looking through the eyepiece of a microscope. He is Russian biologist Elie Metchnikoff, who a few years earlier, in Sicily, had made a revolutionary discovery about the role of white blood cells, which earned him the Nobel Prize in 1908.

During his research on aging and the role of thegut in human health, Metchnikoff first hypothesized that certain microorganisms could be helpful in fighting disease and promoting human well-being. This hypothesis came about by observing the longevity of some Bulgarian populations, and looking for an explanation for this phenomenon in their diet. In particular, Metchnikoff focused on a fermented milk drink, a kind of yogurt , which these populations used to consume.

The microorganisms responsible for this fermentation had been isolated and identified a few years earlier and had been named Lactobacillus bulgaricus precisely in reference to the Bulgarian population (since 1984 they have been reclassified as L. delbrueckii, subspecies bulgaricus).

Metchnikoff’s idea that microorganisms could influence human health by colonizing thegut and exerting aprotective action on it and the entire organism had a strong hold in his period (think it led to the first industrial production of yogurt!). As time went on, however, it was relegated to mere medical practice until, in the mid-1990s, as the scientific evidence to support it accumulated, the idea resurfaced and became one of the driving subjects in health and nutrition-related sciences.

Today, probiotics are not only the subject of intense medical research, but are at the heart of an industry globally worth billions of euros [2].

2001: Official definition of “Probiotic” arrives.

As the role of probiotics in promoting human well-being became clearer, there was a growing need for an unambiguous way to define them. In science, in fact, the first step to better understand something is to name it. In 2001, an official definition of probiotics was finally arrived at, by the FAO andWHO, two United Nations institutes that deal with issues of global significance with regard to food and health. Probiotics are defined as “living microorganisms that, when taken in sufficient quantities, confer a benefit to the host.”

This definition includes many types of products that can be used in different ways (foods, dietary supplements, or drugs) [3] and leaves many questions open and unanswered: what is implied by the fact that microorganisms are “living”? What is the difference between probiotics and milk enzymes? What quantities are considered “sufficient”? What is meant by “host benefit”? Let us respond in order.

What is the difference between probiotics and “common” milk enzymes?

To be called probiotics, the microorganisms in question must not only be alive at the time of intake, but must survive transit within the stomach, a very hostile environment because of the aggressive acids and enzymes it contains. This point Differentiates probiotics from common “milk enzymes: lactic acid bacteria are not expected to survive passage through the stomach, whereas this is a basic requirement for probiotics (also called “live milk enzymes” for this very reason), since their purpose is to colonize the intestinal mucosa and provide benefit by acting at this level.

Studying intestinal colonization by probiotics is not an easy task: one has to move through a jungle of microorganisms that are all very similar to each other, tiny, and present in incredibly high amounts. The development of genetics comes to our aid and allows us to identify the various strains present in biopsies and specimens taken by looking for specific genes that vary not only from species to species, but also from one bacterial strain to another. You will understand well, however, that this work of sampling and analysis is not exactly easy, nor affordable for everyone.

What is the minimum amount of probiotics for gut colonization?

Let’s come to quantities: based on available scientific data, the minimum amount to achieve temporary colonization of the intestine by a microbial strain is at least one billion live cells per day. The use of lower amounts may be allowed only if it is demonstrated that the microorganism in question is capable of colonizing the intestine even at lower doses. The amount of live cells must be stated on the label for each strain and must be guaranteed until the indicated expiration date [4]. As can be seen, these are very precise rules that place not inconsiderable constraints on probiotic manufacturers.

Probiotics: what are the real health benefits?

And now, the hottest topic: the beneficial effects of probiotics on human health. How to define them? How to quantify them? The Ministry of Health ‘s Guideline on Probiotics and Prebiotics states that, according to European Regulation 1924/2006, gut-level colonization of a probiotic alone is not sufficient to support a beneficial effect on health.[4] I mean: it’s fine that your bacteria arrived safely in the gut, but why would that have a positive effect on your health?

What was often found stated on the label was that the product contributes to the “rebalancing of intestinal flora.” But in 2006,EFSA ruled that this health claim was not allowable. Imagine the reaction from those who produce and market probiotics! Italy, one of the world’s leading consumers of probiotics after the US and China, has chosen to allow a “softer” wording in this regard :promotes the balance of intestinal flora” [4].

Yet more and more studies are being done worldwide on theefficacy and usefulness of using probiotics in both the prevention and treatment of certain diseases. So a beneficial effect on health may be there, but it has to be proven through scientific studies. These studies are very lengthy and expensive, require meticulous planning to be useful, and, in some countries, are even hampered by the current bureaucracy, which allows testing only of products registered as drugs.

But what do the hundreds of studies done on probiotics in recent years reveal? What role can these invisible little creatures play in preventing or curing disease? Is their action only at the intestinal level? We will talk about this very interesting topic in the next article, don’t miss it!


[1] Probiotics: definition, scope and mechanisms of action, Gregor Reid, Best Practice & Research Clinical Gastroenterology Volume 30, Issue 1, February 2016, Pages 17-25 Consulted 11/03/2021.

[2] Philip A. Mackowiak, “Recycling Metchnikoff: probiotics, the gut microbiome and the quest for long life,” Front. Public Health, November 13, 2013, Consulted 11/03/2021.

[3] Schlundt, Jorgen. “Health and Nutritional Properties of Probiotics in Food including Powder Milk with Live Lactic Acid Bacteria.” Report of a Joint FAO/WHO Expert Consultation on Evaluation of Health and Nutritional Properties of Probiotics in Food Including Powder Milk with Live Lactic Acid Bacteria. FAO/WHO. Archived from the original on October 22, 2012. Consulted 11/03/2021.

[4] Ministry of Health, Single Commission on Nutrition and Dietetics. GUIDELINES ON PROBIOTICS AND PREBIOTICS Revised March 2018 Consulted 11/03/2021.

Roberto Cighetti



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