Probiotic, prebiotic, synbiotic – what is the difference?

What are probiotics, prebiotics, and synbiotics?

When it comes to microbiome-friendly supplements, we can identify the following categories:

• living bacterial strains,
• nutrients that nourish the beneficial bacteria,
• a mix of probiotics and prebiotics,
• deactivated bacteria.

The differences between these product categories are quite significant and determine how (and whether) the supplement will work.

1. Probiotic

According to the World Health Organization (WHO), probiotics are living microorganisms that, when administered in adequate amounts, provide health benefits to the host. They are selected strains of bacteria or yeast cultures that support health by modulating or maintaining a healthy microbiome. Probiotics can include both bacteria and yeast strains.

Probiotic strains should be specifically named and classified using three components:

• a generic term, such as Lactobacillus.
• a species name, such as rhamnosus.
• a strain designation (alphanumeric code), such as GG.

Proper identification of a strain, its potential benefits and whether it qualifies as a probiotic is possible only if the full three-part name is provided.

In food labelling, manufacturers sometimes list abbreviated strains trade names, such as Bifidus regularis; however, this is merely a colloquial name used for marketing purposes. In scientific terms, Bifidus regularis is actually Bifidobacterium animalis DN-173010.

Important! Not every bacterial strain is probiotic. For example, various bacterial strains used in milk fermentation are not formally probiotics. They fail to meet all the probiotic definition criteria, which implies they do not have scientifically proven health benefits for the host.

Remember, probiotics are strain-specific, which is a relevant factor when selecting a product (and which we will refer to). It means that a particular bacterial strain may help with one condition but be entirely ineffective for another. Probiotic efficacy is always assessed in relation to the strain and its intended purpose. Importantly, the health-promoting properties of a probiotic strain are unique to that strain, not the entire species or genus.

Example: Lactobacillus rhamnosus LGG has been proven to reduce the risk of upper respiratory tract infections; however, it does not mean that every Lactobacillus bacterium “boosts immunity” or “prevents colds”.

Probiotics can be single-strain (focused on a specific benefit or a group of benefits resulting from supplementation of a particular strain) or multi-strain (containing two or more probiotic strains with different or complementary effects).

Interesting fact: Probiotics include subcategories that offer unique benefits. A popular group are psychobiotics, which are probiotics that, when consumed in appropriate doses, affect the gut-brain axis. They improve the mental health of patients suffering from psychological disorders and alleviate symptoms of depression, irritable bowel syndrome, and chronic fatigue. They target the interaction between the brain and the microbiome.

2. Prebiotic

Prebiotics are inanimate food components that positively affect the host's health by modulating the gut microbiota. Prebiotics are not microorganisms, but they are a food source for gut microorganisms. They indirectly promote the health of the microbiome (and the entire organism) by nourishing the microorganisms already present in the system and stimulating their diversity.

However, in order for a substance to be considered a prebiotic, it must meet the following criteria:

• resistance to digestion in the upper parts of the digestive tract,
• a positive impact on the host's health,
• fermentation by the gut microbiota,
• selective stimulation of the growth of beneficial bacteria.

Consuming prebiotics can offer numerous health benefits. Most importantly, it promotes an increase in the number of beneficial bacteria in the intestines and helps lower the pH of the intestinal contents. As a result, prebiotics can provide the same advantages as a properly functioning microbiome, from enhancing immune system activity and improving digestive function to better cognitive performance and a reduced risk of certain lifestyle-related diseases.

Prebiotics are divided into several distinct groups:

• Oligosaccharides: fructo- (FOS), galacto- (GOS), isomalto- (IMO), xylooligosaccharides (XOS), and soy oligosaccharides (SBOS).
• Polysaccharides: inulin, resistant starch, arabinogalactan.
• Lactulose
• Polyphenols: resveratrol, quercetin – have been relatively recently included in the prebiotic category.

Prebiotics are widely used in the food industry, for example as sweeteners (e.g., inulin), gelling or thickening agents. They are used in candies, bars, breakfast cereals, protein products and products for diabetics.

However, prebiotics are not just isolated substances added to food by manufacturers or available as supplements. They are also naturally present in unprocessed foods, most often in the form of dietary fibre. If you follow a healthy diet, you consume a significant amount of natural prebiotics! Here are some examples of their sources:

• Legumes (lentils, chickpeas, beans): contain various oligosaccharides.
• Chicory: contains large amounts of inulin and FOS.
• Onion, garlic, and leek: contain inulin and FOS.
• Asparagus: a rich source of oligosaccharides and inulin.
• Artichokes: one of the richest sources of prebiotics in the form of inulin.
• Green bananas: contain resistant starch.
• Apples: rich in pectin, which is referred to as “prebiotic fibre”.
• Grains (oats, barley, rye, buckwheat): contain oligosaccharides, beta-glucans (prebiotic fibre), and arabinoxylans.

Important: Dietary fibre and prebiotics are not always the same. Both dietary fibre and prebiotics are not digested in the digestive tract. However, prebiotics are fermented by specific microorganisms, while dietary fibre is utilised by various groups of microorganisms in the intestines. As a result, while most prebiotics can be classified as fibre, not all fibre qualifies as a prebiotic.

3. Synbiotic

A synbiotic is a combination of a probiotic and a prebiotic, created for their synergistic effects. When taken together, they support each other, leading to better results than when used individually.

Prebiotic components are selected and matched with probiotic ingredients so that the prebiotic stimulates the growth of a specific type of bacteria. For example, oligofructose is combined with bacteria from the Bifidobacterium genus.

Read: How to take care of the immune system from inside?

4. Postbiotic

Besides probiotics, prebiotics, and synbiotics, there are also postbiotics. This term was created to differentiate living bacterial cells (probiotics) from biologically active preparations with deactivated organisms and their metabolites. According to the 2021 definition developed by ISAPP, a postbiotic is a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host.

Postbiotics primarily include the metabolites of probiotic strains and inanimate probiotic bacteria, which are mostly produced during fermentation processes. Although postbiotics do not directly introduce bacteria to the host's intestines, they stimulate the gut microbiome and may offer health benefits. They exhibit anti-inflammatory, immunomodulatory, lipid profile-supporting, and antihypertensive effects. Their effectiveness, similar to that of probiotics, depends on the specific strain.

Interesting fact: One of the most fascinating postbiotics attracting scientific attention is Akkermansia muciniphila. This bacterium, naturally present in the gut microbiome, is also found in human breast milk. Its presence in the microbiome is associated with a lower risk of metabolic diseases.

What makes Akkermansia muciniphila unique? It is one of the few bacteria that resides in the intestinal mucus layer, rather than the lumen of the intestines. It can break down mucin without damaging the intestinal barrier and indirectly produce valuable short-chain fatty acids, which provide numerous benefits.

Its uniqueness also lies in the fact that A. muciniphila retains its health-promoting properties even after pasteurisation, meaning it can be used as a postbiotic. Akkermansia muciniphila is sometimes called the “probiotic of the new generation”.

What to consider when choosing a probiotic supplement?

It is undeniable that the gut microbiome plays a significant role in human health. Supporting it through various methods, such as following a gut-healthy diet, engaging in moderate physical activity, and avoiding harmful substances, is highly recommended.

Probiotics (as well as prebiotics, synbiotics, or postbiotics) can serve as secondary support in maintaining a healthy microbiome. While some probiotic preparations are well-supported by scientific evidence and can be effective for certain health conditions or specific goals, there is no “one-size-fits-all” probiotic. It is therefore important not to consume probiotics without consideration, grabbing the first available product without a clear goal or understanding of the strains that align with that goal.

Not everyone needs to take probiotics to stay healthy.  If you are considering probiotic supplementation simply because you have heard it is “healthy” or “trendy,” rethink that decision.

Here are some important aspects to keep in mind when choosing a probiotic supplement or considering supplementation in general:

1. There’s no “one-size-fits-all” probiotic.

Probiotics are strain-dependent, and their spectrum of effects is usually narrow. There is no universal “probiotic for everything”. Each probiotic product has a different strain composition, and making any ranking of the “best probiotics”, without outlining the specific therapy objective is pointless. Each strain can have distinct effects, so selecting a probiotic should be based on a specific goal or condition.

2. Match the probiotic strain to your needs.

When choosing a probiotic, match the strain (or multi-strain product) to the condition you are dealing with or your goal. Here are some examples of strains with proven effects in certain areas:

• Lactiplantibacillus plantarum 299v supports irritable bowel syndrome (IBS);
• Saccharomyces boulardii helps prevent traveller's diarrhoea;
• Lactobacillus helveticus Rosell supports mental health;
• Lactobacillus Rhamnosus LGG reduces the risk of upper respiratory infections, prevents antibiotic-associated diarrhoea;
• Lactobacillus acidophilus La1 inhibits Helicobacter pylori (a bacterium associated with the peptic ulcer disease).

3. Check the exact strain description on the packaging.

Good probiotic products provide information about the strain, species, alphanumeric code, and the amount of bacteria in the dose (CFU). Based on this information, you can choose a probiotic that meets your current needs. Products that fail to specify the exact probiotic strains or the bacterial count they contain should be avoided. Not providing this information goes against the fundamental principle of choosing probiotics, which is: “The effect of probiotics depends on the strain!”

4. Pay attention to research.

Studies on probiotics vary in quality, scope, and the number of analyses conducted. As a result, there are different degrees of evidence supporting the efficacy of individual strains and formulations. One cannot compare the potential positive effects observed in a single in vitro study with the results of years of clinical research involving a broad patient population.

Some strains, like Lactobacillus rhamnosus GG, which is known for preventing antibiotic-associated diarrhoea, are well-researched, as are multi-strain probiotics supported by clinical evidence. The media frequently highlight promising yet practically unproven claims about the potential benefits of new or lesser-known strains. Be cautious and reasonably optimistic. When selecting a probiotic supplement, consider the level of evidence supporting the specific strain and whether the product has undergone clinical testing.

5. Choose trusted sellers.

Avoid buying any supplements, particularly probiotics, from unverified sellers. Be cautious of products with significantly low prices. Manufacturing high-quality probiotics is expensive. Inexpensive products may lack the declared strains or be ineffective due to low quality.

Along with the risk that probiotics from unverified sellers might be ineffective, there are additional dangers connected to supplementation. Supplements may be contaminated.

The effectiveness of the probiotic products you use depends heavily on their quality. Opting for supplements from reputable brands or probiotics in medicinal form is a safer choice.

6. Ensure proper storage of the product.

The expiration date is crucial for probiotics (and synbiotics). Over time, the number of living bacteria naturally decreases. An expired product may no longer have any probiotic qualities. Be cautious of promotions on probiotics with a soon-to-expire date. Proper storage of probiotics is essential, both after purchase and at the store. When buying probiotics from unreliable sources, you risk paying for an inactive product (and you will not be able to verify this yourself!).

7. Be cautious when selecting the supplements.

You should be aware that one of the biggest challenges in the probiotic industry (as with other dietary supplements) is the lack of universal standardisation in terms of manufacturing process, classification, and research. This means that not all probiotic products on the market are equally effective, and their declared benefits may not align with the actual results. Consumers may find it hard to evaluate this at first glance – there could be variations in the quality of strains (such as bacterial culture purity), the number of colony-forming units (CFU), which does not always align with what is on the label, or the stability of strains over time, both during storage and after opening the package.

^References:

• ^{Merenstein D. et al, Emerging issues in probiotic safety: 2023 perspectives, Gut Microbes (2023), DOI: 10.1080/19490976.2023.2185034}
• ^{Śliżewska K. et al., Prebiotyki – definicja, właściwości i zastosowanie w przemyśle, Żywność. Nauka. Technologia. Jakość, 2013, 1 (86), 5-20.}
• ^{Dinan T. G., Stanton C., Cryan J. F., Psychobiotics: a novel class of psychotropic, ‘Biological Psychiatry’, 74 (10), 2013, p. 720–726, DOI: 10.1016/j.biopsych.2013.05.001, PMID: 23759244.}
• ^{Pelczyńska M. & Bogdański P., Zastosowanie bakterii Akkermansia muciniphila w terapii zaburzeń metabolicznych, Forum Zaburzeń Metabolicznych, 2023.}
• ^{Nature Microbiology, Impact of Akkermansia muciniphila on cholesterol synthesis, Nature Microbiology, 2023.}