The following blog was written by Felicia Tejo, a student dietitian joining Clasado Biosciences for hands-on work experience. Felicia is aiming to build a career in healthcare, with a particular interest in early-life nutrition and gastrointestinal health. She believes in the importance of a holistic approach to healthcare and aims to promote the importance of diet and good nutrition in disease prevention, recovery and the maintenance of optimal health.

What are fermented foods?

Fermented foods are defined by the International Scientific Association for Probiotics and Prebiotics (ISAPP) as foods made through desired microbial growth and enzymatic conversions of food components1. These microorganisms include lactic acid-producing bacteria, fungi, yeast, and moulds, which can alter the taste or texture of a particular food.

Fermented foods can be found in most food stores, well-known examples include yoghurt, cheese, sauerkraut, and salami. Fermentation has been used for centuries in different civilisations and cultures to produce different fermented foods and drinks. Historically, it has been used for food preservation and may have aided the transition from hunter-gatherer to farming communities. In fact, yoghurt consumption in those communities has been linked to improved health and longevity2. With increasing evidence and public awareness of the benefits of fermentation for food quality and nutrition, the popularity of fermented foods has been on the rise. However, it’s a complex topic, and information in the media surrounding fermented foods and their health benefits can sometimes be misleading for the public.

Are all fermented foods probiotic?

Oftentimes, consumers choose fermented foods for their unique taste and perceived health benefits. The use of microorganisms in the production of fermented food has led many to believe that it is a probiotic, but this is not always true. According to ISAPP, probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit on the host1. However, only some fermented foods contain live microorganisms in their final product and may contain inadequate amounts of microorganisms to confer a probiotic effect2. Additionally, probiotic microorganisms need to survive both manufacturing and the digestion process to reach the gut intact and exert their promoted health benefits3

In addition to containing adequate amounts of live microorganisms, probiotics must also contain defined strains of microbes with documented health benefits, which are not required in fermented foods5. Thus, “fermented food” and “probiotics” are not interchangeable. However, some fermented foods may also contain an adequate amount of defined, living microorganisms in the final product that has proven health benefits. These fermented foods are called “probiotic fermented foods”. These probiotic fermented foods are often produced using starter cultures in a controlled environment, to produce consistent products with similar texture, flavour, and microbial composition3.

Table 1: Required Criteria for Fermented Foods and Probiotics, sourced from ISAPP Science

Required Criteria

Fermented Food

Probiotics

Contains an adequate number of microbes to confer health benefits

No

Yes

Microbes are alive at the point of consumption

Not guaranteed

Yes

Microbial strains are defined taxonomically

No

Yes

Safe for Consumption

Yes

Yes

Fermented foods are divided into 2 major groups: those retaining viable microorganisms from fermentation and others without viable microorganisms in the final product. Fermentation microorganisms may be inactive or removed in the final product due to food processing after fermentation (e.g., baking bread), or to maintain quality and increase shelf-life (e.g., pasteurised yoghurt)4. Some examples of fermented foods are included below2,5.

Table 2: Examples of fermented food that may contain live fermentation microbes and fermented food that does not contain live fermentation microbes2,5

May retain live fermentation microbes

Without live microbes (killed or removed)

Dairy

Yoghurt, Kefir, Kombucha, Cheese

Pasteurised yoghurt, Pasteurised kefir, Pasteurised kombucha, Pasteurised cheese

Vegetable

Non-heated fermented vegetables (e.g., fresh kimchi, sauerkraut)

Heat-treated fermented vegetables (e.g., pasteurised kimchi and sauerkraut)

Meat

Non-heated fermented sausage

Smoked fermented sausages

Grains

Some beer

Alcohol (wine, beer, spirits) Bread

Other

Natto

Soy Sauce

Healthcare professionals can support their patients with their awareness of the differences between fermented foods and probiotics. Due to common misconception, caution is required when recommending fermented foods for their probiotic potential, as only fermented foods with defined and live microorganisms with proven health benefits are probiotics. Importantly, healthcare professionals could play a role in educating patients on the difference between fermented foods and probiotics, and in selecting fermented foods with probiotics for maximum health benefit.

The role of prebiotics

Not to be confused with the similar-sounding probiotics category, prebiotics are defined by ISAPP as “a substrate that is selectively utilized by host microorganisms conferring a health benefit”1. Prebiotics are food, usually soluble fibres (e.g., oligosaccharides, B-glucans and inulin) that are undigested by humans and utilised by gut microbiota. As a result, prebiotics improve the host’s health by supporting the growth of beneficial gut bacteria in the gut microbiome. A simple way to differentiate the two is that probiotics add more beneficial bacteria into the gut, while prebiotics nourish and fuel the good gut bacteria that is already present.

Some fermented foods have been reported to contain prebiotics (e.g., exopolysaccharides from cereal fermentation)2. In fermented foods, prebiotics may be available from the food itself or synthesised during fermentation. Hence, the prebiotic content in fermented foods varies greatly due to the different strains and proportions of microorganisms involved, the extent of fermentation and variability in the food composition3. The probiotic and prebiotic capacity of fermented foods are independent of one another. Many fermented foods that may not contain probiotics have been shown to contain prebiotics, such as pasteurised yoghurt. Despite evidence of the presence of prebiotics in fermented foods, evidence supporting health benefits from these prebiotic compounds in fermented food is still very limited.

Click here to read part two, which explores the role of metabolites in fermented foods, potential disadvantages and a summary of discussion.

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