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Do fermented foods contain probiotics?

/in Consumer Blog, ISAPP Science Blog /by KC

By Prof. Maria Marco, PhD, Department of Food Science & Technology, University of California, Davis

We frequently hear that “fermented foods are rich in beneficial probiotics.” But is this actually true? Do fermented foods contain probiotics?

The quick answer to this question is no – fermented foods are generally not sources of probiotics. Despite the popular assertion to the contrary, very few fermented foods contain microbes that fit the criteria to be called probiotic. But this fact does not mean that fermented foods are bad for you. To uphold the intent of the word probiotic and to explain how fermented foods actually are healthy, we need to find better ways to describe the benefits of fermented foods.

Probiotics are living microorganisms, that when administered in adequate amounts, confer a health benefit on the host (Hill et al 2014 Nat Rev Gastroenterol Hepatol). This current definition reflects minor updates to a definition offered by an expert consultation of scientists in 2001 convened by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization. Evident from the definition, a microbial strain is not a probiotic unless a health benefit has been found with its use. At a minimum, the strain should be proven to be beneficial in at least one randomized controlled trial (RCT). Probiotics must also be defined at the strain level through genome sequencing (a strain is a single genotype of a species).

Fermented foods, on the other hand, have no requirement to improve health. Fermented foods are foods and beverages made through desired microbial growth and enzymatic conversion of food components. This definition was recently formulated by an ISAPP consensus panel of scientific experts to affirm the common properties of all foods of this type and to differentiate foods that may look or taste similar but are not made using microbes (Marco et al 2021 Nat Rev Gastroenterol Hepatol). Fermented foods encompass an expansive variety of foods made from animal and plant sourced ingredients and produced from all types of microbial metabolism. The desired characteristics of these foods are frequently how they look, smell, and taste. There no expectation in this definition that fermented foods alter health in any way.

There is also no requirement for fermented foods contain living microbes at the time they are ingested. Foods such as bread, chocolate, and beer are fermented but then are baked, roasted, and/or filtered. This means those fermented foods cannot be probiotic.

Some fermented foods, such as kimchi and kombucha, are typically eaten with living microbes present. However, the microbes in those foods usually do not meet the criteria to be called probiotic. Whether the fermented food was made at home or purchased from the supermarket, studies investigating whether the microbes in those fermented foods are specifically responsible for a health benefit remain to be done. Those foods also do not contain microbes defined to the strain level, nor is the number of living microbes typically known. An exception to this is if specific strains previously shown to provide a health benefit in one or more RCT are intentionally used in the production of the food and remain viable at expected numbers over the shelf-life of that fermented food product. An example of this would be a commercial fermented yogurt that has an added probiotic strain remaining viable at the time of consumption, beyond the strains that carried out the fermentation.

Despite these distinctions between probiotics an fermented foods, the probiotics term has pervaded common lexicon to mean “beneficial microbes”. In contrast to pathogenic or harmful microbes, beneficial microbes are those that are understood to help rather than hurt bodily functions. However, just as we do not assume that all pathogens cause the same disease or result in the same severity of symptoms, we should also not expect that beneficial microbes all serve the same purpose. By analogy, automobiles are useful vehicles which help us to get from place to place. We do not expect that all automobiles perform like those used for Formula 1 racing. Microbes are needed to make fermented foods and may be beneficial for us, but we should not assume that those drive health benefits like established probiotic strains.

What are the consequences of calling fermented foods probiotic when they include undefined numbers of living microbes for which strain identities are not known? One can suppose that there is no harm in labeling or describing those products as “probiotic” or “containing probiotics”. However, by doing so, confusion and misunderstanding is created and too often, spread by journalists, nutritionists, scientists, and medical professionals. For example, news articles in reputable sources have written that foods like kefir, kimchi, sauerkraut made from beets or cabbage, pickles, cottage cheese, olives, bread and chocolate are rich in probiotics. As misuse perpetuates, what becomes of bona fide probiotics shown with rigorous study to benefit health, such as reducing the incidence and duration of diarrhea or respiratory infections? It becomes difficult to know which strains have scientific proof of benefit. Just as there are laws for standards of food identity, we should strive to do the same when describing microbes in fermented foods.

Avoiding the term probiotic when describing fermented foods should not stop us from espousing the myriad of positive attributes of those foods. Besides their favorable sensory qualities, fermented foods are frequently safer and better tolerated in the digestive tract than the foods they are made from. During the production of fermented foods, microbes remove or reduce toxins in the ingredients and produce bioactive compounds that persist long after the microbes that make them are gone.

Even though the living microbes in fermented foods may not rise to the standard of a probiotic, they may provide health benefits. We just don’t have the studies to prove that they do. With more study, we may find that viable microbes in fermented foods work similarly to probiotics in the digestive tract through shared mechanisms. This is already known for yogurts. Yogurt cultures share the ability to deliver lactase to the intestine, thereby improving tolerance of lactose by intolerant individuals. Clinical and epidemiological studies performed on fermented foods already suggest an association between them and different health benefits but as we recently explained (Marco et al 2021 J Nutrition), more work is needed in order to understand if and what benefits these microbes provide.

For now, we should simply continue enjoying the making and eating of fermented foods and reserve the term probiotics for those specific microbial strains which have been shown to improve our health. Marketers should resist labeling products as containing probiotics if their products do not meet the criteria for a probiotic. Indeed, the descriptor “live and active cultures” more accurately reflects the microbial composition of many fermented foods, and should be used until controlled human trials demonstrating health benefits are conducted.

 

Additional resources:

How are probiotic foods and fermented foods different? ISAPP infographic.

Fermented foods. ISAPP infographic.

What are fermented foods? ISAPP video.

Are fermented foods probiotics? Webinar by Mary Ellen Sanders, PhD.

 

What’s the evidence on ‘biotics’ for health? A summary from five ISAPP board members

/in Consumer Blog, ISAPP Science Blog /by KC

Evidence on the health benefits of gut-targeted ‘biotics’ – probiotics, prebiotics, synbiotics, and postbiotics – has greatly increased over the past two decades, but it can be difficult to sort through the thousands of studies that exist today to learn which of these ingredients are appropriate in which situations. At a recent World of Microbiome virtual conference, ISAPP board members participated in a panel that provided an overview of what we currently know about the health benefits of ‘biotics’ and how they are best used.

Here’s a summary of what the board members had to say:

Dr. Mary Ellen Sanders: Probiotics and fermented foods

  • Probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host”.
  • Unfortunately, published assessments of probiotic products available on the market show that these products often fall short of required evidence. For example, their labels may not adequately describe the contents (including genus / species / strain in the product); they may not guarantee the efficacious dose through the end of the shelf life.
  • Contrary to common belief, probiotics do not need to colonize in the target site (e.g. the gut), impact gut microbiota composition, be derived from humans, or be resistant to stomach acid and other gut secretions such as bile.
  • Fermented foods are those made “through desired microbial growth and enzymatic conversions of food components”. The recent increased interest in fermented foods may come from people’s increased awareness of the role of gut microbes in overall health, but it is important to note that we have little direct evidence that the transient effects of fermented food microbes on the gut microbiota actually lead to health benefits. With that said, observational studies suggest that consuming some traditional fermented foods is associated with improved health outcomes.

Prof. Dan Merenstein, MD: Probiotics – How do I know what to prescribe for adult health?

  • A (limited) survey showed that most dietary supplement probiotic products cannot be linked to evidence because they do not provide enough information to determine what evidence exists to support their use – especially strains in the product. However, there are some probiotic products that have robust evidence.
  • Should every adult take a probiotic? The best evidence supports probiotics for improved lactose digestion and for prevention of difficile infection. Probiotics have also been shown to prevent common illnesses; reduce the duration of gut symptoms; and perhaps even reduce antibiotic consumption.
  • Studies will reveal more about the microbiome and about how probiotics work, for whom and for what indications. As with diet, the answer will most likely not be same for each person.

Prof. Glenn Gibson: Prebiotics and Synbiotics

  • A prebiotic is “a substrate that is selectively utilized by host microorganisms conferring a health benefit”. Researchers can test these substances’ activity in various ways: batch cultures, micro batch cultures, metabolite analysis, molecular microbiology methods, CF gut models, with in vivo (e.g. human) studies being required. Prebiotics appear to have particular utility in elderly populations, and may be helpful in repressing infections, inflammation and allergies. They have also been researched in clinical states such as IBS, IBD, autism and obesity related issues (Gibson et al., 2017).
  • A synbiotic is “a mixture, comprising live microorganisms and substrate(s) selectively utilized by host microorganisms, that confers a health benefit on the host.” While more studies are needed to say precisely which are useful in which situations, synbiotics have shown promise for several aspects of health in adults (Swanson et al. 2020): surgical infections and complications, metabolic disorders (including T2DM and glycaemia), irritable bowel syndrome, Helicobacter pylori infection and atopic dermatitis.

Prof. Hania Szajewska, MD: Biotics for pediatric use

  • Beneficial effects of ‘biotics’ are possible in pediatrics, but each ‘biotic’ needs to be evaluated separately. High-quality research is essential.
  • It is important that we view the use of ‘biotics’ in the context of other things in a child’s life and other interventions.
  • Breast milk is the best option for feeding infants
  • If breastfeeding is not an option, infant formulae supplemented with probiotics and/or prebiotics and/or postbiotics are available on the market.
  • Pro-/pre-/synbiotic supplemented formulae evaluated so far seem safe with some favorable clinical effects possible, but the evidence is not robust enough overall to be able to recommend routine use of these formulae.
  • Evidence is convincing on probiotics for prevention of necrotizing enterocolitis in preterm infants.
  • Medical societies differ in their recommendations for probiotics to treat acute gastroenteritis in children – they appear beneficial but not essential.
  • Synbiotics are less studied, but early evidence indicates they may be useful for preventing sepsis in infants and preventing / treating allergy and atopic dermatitis in children.

Prof. Gabriel Vinderola: Postbiotics

  • The concept of non-viable microbes exerting a health benefit has been around for a while, but different terms were used for these ingredients. Creating a scientific consensus definition will improve communication with health professionals, industry, regulators, and the general public. It will allow clear criteria for what qualifies as a postbiotic, and allow better tracking of scientific papers for future systematic reviews and meta-analyses.
  • The ISAPP consensus definition (in press) of a postbiotic is: “A preparation of inanimate microorganisms and/or their components that confers a health benefit on the host”.
  • Postbiotics are stable, so no cold-chain is needed to deliver them to the consumer. Safety is of less concern because the microbes are not alive and thus cannot cause bacteraemia.
  • Research in the coming years will reveal more about postbiotics and the ways in which they can promote human health.

See here for the entire presentation on Biotics for Health.

Probiotics and fermented foods, by Dr. Mary Ellen Sanders (@1:15)

Postbiotics, by Prof. Gabriel Vinderola (@18:22)

Prebiotics and synbiotics, by Prof. Glenn Gibson (@33:24)

‘Biotics’ for pediatric use, by Prof. Hania Szajewska (@47:55 )

Probiotics: How do I know what to prescribe for adult health? by Prof. Dan Merenstein (@1:04:51)

Q&A (@1:20:00)

 

Opportunity for research grants to help understand evidence linking live dietary microbes and health

/in News, ISAPP Science Blog /by KC

For thousands of years, cultures across the globe have been consuming fermented foods, many of which contain diverse and numerous live microbes. Yet scientists are still puzzling over whether a greater intake of live microbes results in measurably better health. As part of long-term efforts to understand evidence for the health benefits of live dietary microbes and identify research gaps, ILSI North America is presenting a grant opportunity for researchers to help assess current scientific evidence for these links.

Researchers are invited to submit grant proposals, which should include the research approach along with anticipated challenges, resources, timeline, and key deliverables. The ILSI North America Gut Microbiome Committee also requests the inclusion of a suggested publication plan for the work. Budgets in the range of $100-150K will be considered. The deadline to submit the proposal is October 30, 2020 at 11:59PM EST. See here for more details.

ISAPP is supporting long-term efforts in this topic area. Its latest effort is the publication of a review paper (in press) on the links between dietary live microbes and health, called Should there be a recommended daily intake of microbes? The paper is authored by ISAPP board members Prof. Maria Marco, Prof. Colin Hill, Prof. Bob Hutkins, Prof. Dan Tancredi, Prof. Dan Merenstein, and Dr. Mary Ellen Sanders along with well-known nutrition researcher, Prof. Joanne Slavin.

ILSI North America is a non-profit scientific organization whose mission is to advance food safety and nutrition science for the benefit of public health. The organization engages academic, government, and industry experts by conducting­ research projects, workshops, seminars, and publications.

 

How do probiotics stay alive until they are consumed?

/in Consumer Blog, ISAPP Science Blog /by KC

By Prof. Gabriel Vinderola PhD,  Associate Professor of Microbiology at the Faculty of Chemical Engineering from the National University of Litoral and Principal Researcher from CONICET at Dairy Products Institute (CONICET-UNL), Santa Fe, Argentina

See the Spanish version of this blog post here.

As a professor, most of my days are spent with people from the academic and scientific world. But through some outreach activities, I am also fortunate to interact with many people who are not scientists by training, but have curious, scientific minds. One question I am often asked is, “Is it really possible for probiotics to still be alive when they are dried and in a capsule?” The answer is yes. Let me provide some basic background on probiotics and explain my response.

The idea of consuming live microbes to promote health is not new. Back in 1907, Élie Metchnikoff, a disciple of Louis Pasteur, the father of microbiology, associated the intake of fermented milks containing live lactobacilli, with a prolonged and healthy life in Bulgarian peasants (see here). This idea was later captured by the concept of probiotics: live microorganisms that, when administered in adequate amounts, confer a health benefit on the host (Hill et al. 2014). Four simple and pragmatic criteria allow one to conclude if specific strains of microorganisms qualify as a probiotic for use in foods and dietary supplements. Probiotic strains must be (i) sufficiently characterized; (ii) safe for the intended use; (iii) supported by at least one human clinical trial showing they are effective; and (iv) alive in the product at an efficacious dose throughout shelf life (Binda et al. 2020). Being alive at the moment of consumption is one of the key characteristics of probiotics.

Life is the condition that distinguishes animals and plants from inorganic matter. Life includes the capacity for growth, for reproduction and for metabolic activity. In order to sustain life, certain environmental conditions must be met, but these differ for different organisms. For microbes, the availability of water and nutrients, adequate temperature and pH (acidity), and the absence of growth inhibitors are essential conditions. However, it is possible to manipulate certain conditions to bring about a state where growth may be put in “stand-by mode”, yet the microbe remains alive. We cannot imagine ourselves in a condition where life is preserved even without any metabolic activity, but for microbes it is possible. Probiotics can be in foods (yoghurts, fermented milks, fruit juices, cereal bars) or in food supplements (capsules, compressed pills) in a “hibernation” state, characterized by no growth, no reproduction and no metabolic activity, waiting for the proper conditions to come back to full metabolic life. This occurs when the microbes reach the gut, which has proper temperature, nutrient availability, lack of inhibitors, adequate acidity and water. Thus, in case of microbes, there is an uncoupling of life and metabolic activity. Even without having any metabolic activity, they can still be alive, but in a dormant state.

Open a food supplement containing probiotics and you will probably find a white dry powder. This is what the microbes may look like in their dormant state, due to a technological process called freeze-drying or lyophilization. Freeze-drying is a two-stage process where cells are first quickly frozen at very low temperatures (-40 to -70°C, or less, using liquid nitrogen for example). Then, frozen water is removed by a gentle process of evaporation at low pressure and temperature, called sublimation. This process removes most of the water from around and inside the cells, leaving the microbes in a dormant state. Water activity is scientists’ way of measuring water availability for the microbes. This technological measure ranges from 0 (no water) to 1 (pure water). A water activity close to 0 impairs growth. In food supplements, freeze-drying leaves water activities less to 0.2, ensuring that no metabolic activity will take place during the shelf life of the product.

Bifidobacteria cells (circled in red) freeze-dried in a probiotic powder. This is a scanning electron microscopy image amplified 10,000 times. Cells are embedded in dry polydextrose.

So yes, probiotics in food supplements are alive in their own way. This is the case also for probiotics included in certain foods such as cereal bars. In case of food products with water activities closer to 1, such as yogurts, fermented milks, cheeses or fruit juices containing probiotics, the factor that limits metabolic activity is the low temperature at which these products are stored, combined in certain cases (yogurts, fermented milks, fruit juices) with the low pH (or high acidity) of these products. The combination of low temperature and acidity is effective in maintaining probiotic cells in a dormant state, impairing any metabolic activity that may lead to cell stress and cell death along the shelf life of the product. Yet, even while tightly controlling factors that impair metabolic activity, some cell death may occur during the shelf life of probiotics in the products that deliver them. In this case, responsible manufacturers are sure to add extra probiotic cells so that the necessary amount of viable cells needed to deliver a health effect are present through the end of the shelf life of the product.

In both probiotic foods and food supplements, the number of viable cells is commonly expressed as a certain number of colony forming units, or by the abbreviation “CFU”. As probiotics are present in high concentrations, the number of viable cells often reaches into the billions within a capsule or in a serving of yogurt. To be able to count such enormous numbers of cells, microbiologists must make serial dilutions of the probiotic product. Then, they will put a small drop of a dilution on the surface of a Petri dish containing a culture medium on which probiotics will grow. Each probiotic cell (or clump of cells) will grow in place and form a visible colony that can be observed to the naked eye, and counted.

Agar plate containing colonies of a probiotic bacteria. Cells deposited on the surface of the agar plate duplicated several times until forming a visible amount of cells: a colony.

In brief, live probiotics are present in food and supplements, but in a state of life different to that of higher organisms where metabolic activity is taking place at all times. During shelf life, the metabolic activity of probiotics is stopped by freeze-drying them (food supplements) or by a combination of low temperature and acidity (yogurts and fruit juices, for example). Active growth returns when these microbes enter out gut and find the proper conditions of nutrients, temperature, acidity and water to be active and deliver their health effects.

Is probiotic colonization essential?

/in Consumer Blog, ISAPP Science Blog /by KC

By Prof. Maria Marco, PhD, Department of Food Science & Technology, University of California, Davis

It is increasingly appreciated by consumers, physicians, and researchers alike that the human digestive tract is colonized by trillions of bacteria and many of those bacterial colonists have important roles in promoting human health. Because of this association between the gut microbiota and health, it seems appropriate to suggest that probiotics consumed in foods, beverages, or dietary supplements should also colonize the human digestive tract. But do probiotics really colonize? What is meant by the term “colonization” in the first place? If probiotics don’t colonize, does that mean that they are ineffective? In that case, should we be searching for new probiotic strains that have colonization potential?

My answer to the first question is no – probiotics generally do not colonize the digestive tract or other sites on the human body. Before leaping to conclusions on what this means for probiotic efficacy, “colonization” as defined here means the permanent, or at least long-term (weeks, months, or years) establishment at a specific body site. Colonization can also result in engraftment with consequential changes to the gut microbiota composition and function. For colonization to occur, the probiotic should multiply and form a stably replicating population. This outcome is distinct from a more transient, short-term (a few days to a week or so) persistence of a probiotic. For transient probiotics, it has been shown in numerous ways that they are metabolically active in the intestine and might even grow and divide. However, they are not expected to replicate to high numbers or displace members of the native gut microbiota.

Although some studies have shown that digestive tracts of infants can be colonized by probiotics (weeks to months), the intestinal persistence times of probiotic strains in children and adults is generally much shorter, lasting only few days. This difference is likely due to the resident gut microbiota that develops during infancy and tends to remain relatively stable throughout adulthood. Even with perturbations caused by antibiotics or foodborne illness, the gut microbiome tends to be resilient to the long-term establishment of exogenous bacterial strains. In instances where probiotic colonization or long-term persistence was found, colonization potential has been attributed more permissive gut microbiomes specific to certain individuals. In either case, for colonization to occur, any introduced probiotic has to overcome the significant ecological constraints inherent to existing, stable ecosystems.

Photo by http://benvandenbroecke.be/ Copyright, ISAPP 2019.

This leads to the next question: Can probiotics confer health benefits even if they do not colonize? My answer is definitely yes! Human studies on probiotics with positive outcomes have not relied on intestinal colonization by those microbes to cause an effect. Instead of colonizing, probiotics can alter the digestive tract in other ways such as by producing metabolites that modulate the activity of the gut microbiota or stimulate the intestinal epithelium directly. These effects could happen even on short-time scales, ranging from minutes to hours.

Should we be searching for new probiotic strains that have greater colonization potential? By extension of what we know about the resident human gut microbiota, it is increasingly attractive to identify bacteria that colonize the human digestive tract in the same way. In some situations, colonization might be preferred or even essential to impacting health, such as by engrafting a microbe that performs critical metabolic functions in the gut (e.g. break down complex carbohydrates). However, colonization also comes with risks of unintended consequences and the loss of ability to control the dose, frequency, and duration of exposure to that particular microbe.

Just as most pharmaceutical drugs have a transient impact on the human body, why should we expect more from probiotics? Many medications need to be taken life-long in order manage chronic conditions. Single or even repeated doses of any medication are similarly not expected to cure disease. Therefore, we should not assume a priori that any observed variations in probiotic efficacy are due to a lack of colonization. To the contrary, the consumption of probiotics could be sufficient for a ripple effect in the intestine, subtly altering the responses of the gut microbiome and intestinal epithelium in ways that are amplified throughout the body. Instead of aiming for engraftment directly or hand-wringing due to a lack of colonization, understanding the precise molecular interactions and cause/effect consequences of probiotic introduction will lead to a path that ultimately determines whether colonization is needed or just a distraction.