What are fermented foods?
Yogurt, kefir, sauerkraut, kimchi, wine, beer… There is a long list of fermented foods and beverages that have been consumed by humans for centuries. Almost every culture has them in their traditional diets and they can be considered the first processed foods ever made.
These foods go through the process of fermentation which, in a time where there were no fridges, freezers, preservatives, etc, improved their durability and safety for human consumption – they kept for longer without “going off”. In addition, the process of fermentation improves the taste, smell and texture (organoleptic properties) of the original foods.
How does fermentation work?
The general process of fermentation consists in taking a food, adding microorganisms to it and wait for them to produce another food with different taste, smell, appearance and, in many cases, health benefits for the consumer.
Sounds simple – and it is, compared to many technologies used nowdays by the food industry. But, though the basic mechanism is elegant and simple, the process is delicate and complex at the microscopic level. Microbial growth must be controlled and the microbes to use will generally depend on the original substrate (food). For example, foods with simple sugars are usually fermented by yeasts or lactic acid bacteria or starchy foods with molds. Moreover, minor alterations during fermentation could produce a very different food. To avoid this, microbial communities must be resilient so that the composition of microbes remains stable throughout the whole proccess.
And what foods can be fermented? Pretty much anything. Meat, fish, diary, vegetables, legumes, cereals, fruits, roots… The different combinations of food and microorganisms result in a huge variety of fermented products.
Benefits of fermented foods
Beside improving the preservation and organoleptic properties of the original foods, they are also recognised for promoting health.
Some of the benefits are well known. For example, people who have lactose intolerance can better tolerate yogurt and cheese. This is because some of the lactose in the milk is fermented during the process. In yogurt, lactose tolerance is also improved by the release of β-galactosidase by the microbes in yogurt cultures because β-galactosidase is an enzyme that, again, breaks down lactose.
Another microbial enzyme, linoleate isomerase, is used by many lactic acid bacteria to produce conjugated linoleica cid. This is a fatty acid with atherosclerosis protective capacity.
Lactic acid bacteria are particularly beneficial in several ways. Apart from the ability to ferment lactose and produce conjugated linoleic acid, as mentioned above, they can also break down protein and convert phenolic compounds into bioactive metabolites.
Grains, nuts and legumes contain phytic acid. This acid is protective for the plant but is an anti-nutrient for humans. Fermentation removes or greatly reduces phytic acid, making these foods more digestible and less toxic for us.
In addition, Science has also shown a wide range of health benefits collectively attributed to fermented foods, like:
- protection from type 2 diabetes
- weight maintenance
- protection from cardiovascular disease
- reduction of overall mortality
- better mood and brain activity
- better glucose metabolism
What is the impact of fermented foods in the gut microbiota?
Many traditional fermented foods and drinks contain a good quantity (106 – 109 cells/g) of live microbes when consumed, and a large proportion can survive their journey to the gut. This means that the number and diversity of the gut microbiota increase when we eat or drink these foods. This, however, seems to be transient, meaning that the newly introduced microbes do not make our gut their home.
Although for a short period of time, it is likely that the fermentation microbes have some effect in the composition and function of the already established gut microbiota. For instance, they can produce products that the indigenous microbiota can use, or they may inhibit or stimulate the growth of some microbes or they may impact host health in a manner that will then impact the microbiota. Currently, scientific evidence of these mechanisms and their magnitude is lacking.
What seems to be true is that their possible impact on the resident gut microbiota is short-term and a more long-lasting effect would require daily intake of fermented products.