Plant-based fermented beverages are seen as heralding a new dawn in healthy eating. They are very much linked to helping us develop and sustain a healthy gut microbiota. Developing a fermented beverage based on plants will be influenced by understanding the effects they have on the microbiota of the gut. Do we consider prebiotics such as the presence and addition of fibre? What about probiotics which are part of the fermentation process and then there are postbiotics which are now products of gut fermentation?
At the moment there is very little good quality data to support the view that fermented beverages actually have a solid health benefit and would be beneficial to healthy living. From the outset, there is still a need to understand if these fermented plant-based beverages will be any ‘good’! Recent commentators on the subject are also highlighting that dietary recommendations are needed for living microbes along with standards for the kinds and amount of microbes in beverages to generate a notable health benefit and whether there are risks attached.
Basic Digestion And The Role of Fibre
When we ingest food as part of our diet we would expect it to be digested and for our intestine to absorb food products and components. Something like 95% of our food intake is digestible. This is mainly protein, fats, vitamins and minerals, and carbohydrates. We also have undigested food materials left in the stomach which is generally fibre but also products that come from the initial fermentation of the beverage say we ingested as well as those products produced by our gut bacteria, and these we excrete.
When dietary fibre became interesting, we looked at the soluble dietary fibre rather than the insoluble and undigested fibre and other food components. In later years it became apparent the undigested componentry was almost as important as the digested material. Intestinal fermentation was influenced by these undigested materials because gut microbes in turn create lots of byproducts such as vitamins, short-chain fatty acids (SCFAs) including butyrate, for example. These are absorbed by the gut and are used in various biochemical processes for energy production, immune functions etc.
we also produce intestinal secretions such as mucus to help the flow of food and excreta through the intestine. Mucus, amongst other secretions is also digested by our gut microbiota.
When gut health is good, then our overall healthiness is better and we can trace this all the way back to the food we eat.
The Microbiome Revolution
Back in ancient Greece, Hippocrates stated that:-
“All disease begins in the gut”
Moving fast-forward to the present day and we can find clinical evidence that reinforces that prescient statement. Ley et al. (2006) published an article reporting research showing gut microbes were associated with obesity. The researchers looked at 12 obese people who were genetically not related. They were kept on a fat or carbohydrate restricted diet and their weight and measures for obesity monitored over a year. They looked at the gut bacteria and found that a particular group of bacteria, the Bacteroidetes increase in population size which correlated with weight increase. It may be a small study but it piqued the interest of the scientific community. It was demonstrating an association with the gut microbiome and not just gut health that had an impact on a chronic condition such as obesity.
How Fibre Affects the Gut!
A well illustrated description was made by Dayib and Slavin in the Journal Current Opinion of Metabolic Care (2020). Dietary fibre has an impact throughout the digestive tract, from the mouth through to the anus. Most interest focuses on the stomach, small and large intestine but every part of the digestive tract has its part to play.
Fibre makes chewing (mastication) food more difficult and length as a process but it means more saliva is produced to help ease the passage of food down the oesophagus to the stomach as well as adding various digestive enzymes. In the stomach, the fibre physically increases its size, usually termed gastric distension and delays emptying. Throughout the passage through the intestine from stomach onwards, there is a much slower level of digestion generally, along with delayed nutrient absorption – all because of the presence of fibre. At the same time, the blood glucose spiking of the blood is blunted and the insulin response is curtailed. There are also important alterations in levels of gut hormones such as ghrelin, GLP-1 and PYY.
The postbiotic activity of fibre is also interesting. There is fermentation in the larger intestine as in the colon, of the gut of undigested carbohydrate which is worked on by microbiota producing the SCFAs, changes to pH and critical changes to the composition of the gut fauna/flora in the digestion process.
The Many Benefits of Gut Microbes
Gut microbes have many more benefits than we might first have thought. For starters, they generate extra energy on top of our body’s metabolic processes through the production of these short-chain fatty acids which are used to feed intestinal cells. A number of vitamins such as vitamin K and biotin are generated by microbiota in the colon for example.
The gut microbes destroy potential carcinogens and prevent colonization by certain pathogens because of the pH changes they product in the gut. They are also capable of selectively harvesting nutrients. In some instances this helps with mineral absorptions, especially of calcium.
Most of our immune cells are found in the gut. They are also associated with the development and extension of the adult and mature immune system.
Prebiotics In Plant-Based Fermented Beverages
An ISAPP Consensus Statement from 2017 defined prebiotics succinctly. These are substances that are selectively used by host microorganisms and confer on them a health benefit. They are mainly CLAs and PUFAs, oligosaccharides such as FOS, inulin, MOS, XOS and GOS, human milk oligosaccharides and phenolics and phytochemicals. They are also the fermentable elements found in dietary fibre.
The non-prebiotic components are probiotics, fats, proteins, antibiotics, vitamins and the poorly fermented forms of dietary fibre.
The Probiotics
The bacteria that are consumed in foods such as plant-based fermented beverages for example.
The WHO defines a probiotic as:
Live microorganisms that when administered in adequate amounts confer a health benefit on the host.
These live microbes can be formulated into all sorts of products such as food, dietary supplements, drugs and so on. Good examples include E.coli, Bacillus, Lactobacillus, Bifidobacterium, yeasts such as Saccharomyces cerevisiae. They all have health benefits.
Most fermented products are heat treated and processed so their natural probiotics are destroyed in such processing. The place to traditionally find probiotics is in wine, vinegar, cider and beer, fermented meat, kombucha, sourdough bread and sauerkraut. A large number of fermented dairy products exist such as natural cheese and yogurts, along with kefir and buttermilk.
Any cultures contained in the food may or may not be considered probiotic. It depends on their bacterial levels when eaten and whether the bacteria contained in the food actually confer a health benefit. At the moment it is unclear if the cultures need to be alive or dead for benefits to be obtained. What is apparent is that fermented foods are recognised for their considerable health properties.
Is there any clinical evidence to support the presence of probiotics? One study (Skonieczna-Zydecka et al., 2020) was a meta-analysis of various randomized controlled trials which supported a number of viewpoints on probiotics. They considered 61 studies involving 5422 people. Only studies with more than 20 adults were examined and the range of the intake was 67 plus or minus 39 days. A number of end-points were examined. Of the strains, most involved Bifidobacterium and Lactobacillus alongside Streptococci, Pediococci and Enterococci genera. The daily probiotic dose was between 10E6 and 10E10 CFUs – a large variation. Generally, there was poor quality attributed to these probiotic studies which makes systematic review very difficult. Definite conclusions could not be drawn and a ‘Gold Standard’ methodology is still required to make clinical judgements around probiotic studies.
At The Moment
The FDA does not approve probiotics for preventing or treating any health problem. In fact, probiotics have been linked to severe health issues including dangerous infections as well as food safety. They can also compromise people with weak immune systems. It’s not clear either if probiotics all have the same effect and it is thought that these are strain specific. Some producers of probiotic yogurt think only their particular bacteria is suitable. The dosage level is unclear and it does not keep either with shelf-life. Whilst the consumer is interested in them, regulation is poor and so it revolves around a halo effect. It is thought that the unhealthy would benefit from probiotics in fermented beverages but it is not yet proven.
An ISAPP panel developed a consensus statement on fermented foods. This panel reviewed how fermented foods are regulated and discussed efforts to include them as a separate category in national dietary guidelines. Their definition:
“Foods made through desired microbial growth and enzymatic conversions of food components.” (Marco, M et al., Nature Reviews).
One study examined whether a vegan or vegetarian diet influences or is associated with the microbiota composition in the gut (Treffish et al., 2020). This group systematically reviewed 16 studies examining the gut microbiota in omnivores, vegetarians and vegans. There was absolutely no consistent association between these diets. It is possible that the consistency would be due to individuality where microbes are concerned and difference sin the applied approaches. To get a better understanding of this, standardized methods with good taxonomical and functional resolutions is required.
The American Gut Project
The project has found that microbes in the gut are much more diverse than originally thought. Migration from a non-westernised nation to the USA is associated with a loss of gut microbiome diversity. Subjects who ate more than 30 types of plant foods weekly had more diversity than subjects who ate only 10 types of plant food. So, diversity has not been linked to a health outcome but it is thought to be a good thing although the evidence is not available.
In summary, lots of people are interested in fermented plant food beverages but it’s not clear if they will improve gut health as there are no accepted health outcomes. the links however between changes in the microbiota and health are developing but there is no accepted ‘healthy’ microbiota.
References
Ley, R. E., Turnbaugh, P. J., Klein, S., & Gordon, J. I. (2006). Human gut microbes associated with obesity. Nature, 444(7122), pp. 1022-1023.
Skonieczna-Żydecka, K., Janda, K., Kaczmarczyk, M., Marlicz, W., Łoniewski, I., & Łoniewska, B. (2020). The effect of probiotics on symptoms, gut microbiota and inflammatory markers in infantile colic: a systematic review, meta-analysis and meta-regression of randomized controlled trials. Journal of Clinical Medicine, 9(4), 999 (Article).
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