Synbiotic: more than just a probiotic + prebiotic?

In May 2019, the International Scientific Association for Probiotics and Prebiotics (ISAPP) formed an expert panel to address the definition and scope of the term synbiotic.1 The aim of the panel was to  provide clarity and guidance on the appropriate use of the term synbiotic, and to describe the evidence required to demonstrate health benefits and establish safety.


An Updated Definition

Whilst the previous synbiotic definition was longwinded and unclear, it is now more simply defined as “a mixture comprising live microorganisms and substrate(s) selectively utilized by host microorganisms that confers a health benefit on the host”.

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Categorisation of synbiotics

There are two ways to classify a synbiotic; a synergistic synbiotic or a complementary synbiotic.

A synergistic synbiotic is when the live microorganism(s) are combined with a selectively utilised substrate(s) – i.e. the substrate will increase the growth and/or activity of the co-administered microorganism(s), and together they provide a health benefit on the host.1

A complementary synbiotic is the combination of a probiotic and prebiotic, working together to provide a health benefit.2 In this case, both the live microorganism(s) and substrate(s) must meet the criteria for a probiotic3 or prebiotic4, independently. 

Differentiating synbiotics in this way ensures there are fewer limitations in developing synbiotics, encouraging product innovation.1


Characterisation needed for synbiotics

The structure and purity of the substrate needs to be characterised, and the taxonomy, safety, efficacy and purity of the live microorganism(s) should be clearly and accurately described, to meet regulatory standards for the product category.1 When the live microorganisms are combined with a substrate in a medium, the dosage of the live microorganism required to confer the stated health benefit must be delivered throughout the shelf-life. 


Necessary Evidence for Synbiotics

According to ISAPP, different types of studies must be designed for synergistic synbiotics and complementary synbiotics. 

A synergistic synbiotic must have at least one study demonstrating both selective utilisation of the substrate and a health benefit in the target host. For complementary synbiotics, the dose of both the prebiotic and probiotic must  be stated, but it is only necessary to show a health benefit, in the target host, of the combined ingredients, and is unnecessary to show selective utilisation of the prebiotic substrate as this would already be established.1


Safety Measures for Synbiotics

A safety assessment is required for a synergistic synbiotic to show that the microorganism will improve functionality in the presence of a substrate such as increased growth, or modified metabolic or physiological activity in vivo.1

In order to be established as probiotics and prebiotics a safety assessment is required4,5, therefore a complementary synbiotic  formulated with these components may be presumed safe for the intended use. However, novel formulations must be suitably assessed for safety.1


The new ISAPP definition for the term synbiotic is an advancement in synbiotic research, allowing a better understanding among researchers and enabling better communication to consumers. 



1. Swanson et al. (2020) Nature Reviews Gastroenterology & Hepatology doi:s41575-020-0344-2.

2. Kolida and Gibson. (2011) Annual Review of Food Science and Technology 2:373–393.

3. Hill et al. (2014) Nature Reviews Gastroenterology & Hepatology 11:506-514. 

4. Gibson et al. (2017) Nature Reviews Gastroenterology & Hepatology 14:491-502