Fermented foods and health

Fermented foods are often regarded as superfoods or wrongly equated to probiotics. In this article we discuss what are fermented foods and what is the relationship between fermented foods and health.

What are fermented foods?

Fermented foods are those which are transformed by the action of microorganisms. To differentiate fermentation from spoilage, the International Scientific Association for Probiotics and Prebiotics utilises the following definition: “foods made through desired microbial growth and enzymatic conversions of food components” (1).

Fermented foods are consumed all over the world and is estimated that there are over 5000 varieties (1, 2).

During fermentation, microbes feed on the source food and produce metabolites which change its physical and chemical properties such as taste, smell, texture, appearance and nutritional composition (1, 3).

Which foods can be fermented?

Pretty much anything! This includes vegetables (including roots and tubers), fruits, cereals, legumes, dairy foods, meat, fish (2, 3).

Types of fermented foods

There are different ways to classify fermented foods.

By their live microorganism content (1)

1. Foods which contain live microorganisms, such as yoghurt, sour cream, kefir, most cheeses, miso, natto, tempeh, fermented vegetables that have not been pasteurised (e.g. sauerkraut, kimchi found in the refrigerated section of the store), naturally fermented cured meats, most kombuchas and some beers
2. Foods which do not contain live microorganisms, such as sourdough bread, pasteurised fermented vegetables, sausages, soy sauce, vinegars and kombuchas, fermented alcoholic drinks (e.g. wine, most beers, spirits), roasted coffee and cacao beans

By their fermentation method (3)

1. Wild or spontaneous ferments, which are fermented by microorganisms naturally present in the source food, e.g. sauerkraut and kimchi
2. Culture-dependent ferments, made by adding starter cultures, such as keffir and kombucha

Fermented foods vs probiotics

The first distinction between fermented foods and probiotics is that food is food and probiotics are microorganisms. Moreover, not all fermented foods contain live microorganisms and, most importantly, not all microorganisms are probiotics. By definition, probiotics must be beneficial to the host organism.

Because food labelling regulations can be quite strict and food manufacturing can be quite variable, we cannot always assume that fermented foods contain probiotics even if they are found in the refrigerated section of the supermarket, unless the label contains a specific statement.

On the flip side, this does not mean that fermented foods without proven probiotic content are not healthy. They could be healthy due to the food composition itself, or they may contain probiotics that have not been identified or documented.

Fermented foods and health

Fermented foods are normally regarded as healthy. Every traditional culture has staple fermented foods. Unfortunately, in modern times many foods are labelled as “superfoods” just because they are fermented, which is not necessarily accurate.

A lot of the evidence supporting the health benefits of fermented foods is based on animal or in vitro studies. The exception seems to be yoghurt and other fermented dairy products, which human clinical studies have found beneficial for the management of obesity and a reduced risk of type 2 diabetes, cardiovascular disease (1, 2) and mortality (2).

Of course, the lack of evidence does not mean other fermented foods do not confer health benefits.

Benefits associated with fermentation

Fermentation make foods healthier by:

1. creating an environment with high acidity and other characteristics which inhibit the growth of pathogenic microbes (1, 2)
2. degrading toxic compounds inherently present in some plant foods (1, 3)
3. degrading proteins that may elicit an immune reaction (e.g. amylase-trypsin inhibitor in wheat) (1)
4. degrading anti-nutrients such as phytic acid, thereby increasing absorption of nutrients present in the food (1, 3)
5. reducing the concentration of simple sugars, decreasing the energy content and glycaemic index of the food (1)
6. breaking down food components such as disaccharides (e.g. lactose), polysaccharides, proteins, fats and fermentable carbohydrates (i.e. FODMAPs) to facilitate digestion (1, 2, 3)
7. increasing the bioavailability of polyphenols (1, 3)
8. generating new nutrients (e.g. vitamins, amino acid derivatives, antioxidants) (1, 2)
9. the probiotics present in the food (more on this below) (1)

Note: the processes outlined above do not necessarily apply to all fermented foods

Probiotics in fermented foods

A portion of the probiotics present in some fermented foods (e.g. some Lactobacillus species) can make its way to our intestines where they can have beneficial effects, despite evidence suggesting their stay is short (1, 2, 3).

Beneficial effects may include generating bioactive compounds such as short-chain fatty acids (SCFA) (1) and exopolysaccharides which may modulate the immune system and lower cholesterol (2), maintaining gut integrity (in part thanks to SCFA), and altering the microbial composition of the gut (1, 2, 3). On the latter, there is some evidence that fermented dairy products (e.g. kefir and yoghurt) may alter the gut microbiome composition in individuals with gut health conditions (3, 4). Although there are some studies reporting microbial composition changes after consumption of other fermented foods, no compelling conclusions have been made at this stage (3, 4).

Risks associated with fermented foods

Even though fermented foods are generally very safe, there are some risks to be aware of (1):

1. Some foods such as soft and fresh cheeses can be contaminated with pathogenic bacteria, this is why pregnant women and immuno-compromised individuals are told to avoid them
2. Some metabolites produced by fermentation can be detrimental to health when consumed in large quantities, e.g. alcohol
3. Some metabolites produced by fermentation can cause symptoms in sensitive individuals, such as histamines and other amines produced in cheese, wine, chocolate, etc.

References

1. Marco ML, Sanders ME, Gänzle M, Arrieta MC, Cotter PD, De Vuyst L, et al. The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on fermented foods. Nat Rev Gastroenterol Hepatol [Internet]. 2021;18(3):196–208. Available from: https://doi.org/10.1038/s41575-020-00390-5
2. Leeuwendaal NK, Stanton C, O’Toole PW, Beresford TP. Fermented Foods, Health and the Gut Microbiome. Vol. 14, Nutrients. 2022.
3. Dimidi E, Cox SR, Rossi M, Whelan K. Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease. Vol. 11, Nutrients. 2019.
4. Stiemsma LT, Nakamura RE, Nguyen JG, Michels KB. Does Consumption of Fermented Foods Modify the Human Gut Microbiota? J Nutr. 2020 Jul;150(7):1680–92.

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