This post was written by one of our contributors; registered Associate Nutritionist (ANutr) – Rachael Matthews
If you’ve done any research on health and well-being in the past few years, you are likely to have come numerous articles and papers discussing the emerging evidence on our gut health and its importance to our overall well-being. Unlike other fad diets that come in and out of fashion, gut health is not a trend, it’s a scientific breakthrough. As more and more research are collected, the positive effects of a healthy gut has been proven to go far beyond just our digestive system, with increasing amounts of studies showing a heathy microbiota can:
- Influence your mood positively by decreasing anxiety and depression (1) through the neurotransmitter serotonin (the happy hormone). 90% of the body’s serotonin is made in your gut. Here, serotonin helps to control your appetite, libido and blood clotting
- Improve immune function (2), 70% of your immune system is directly influenced by the bacteria found in your gut
- Influence behaviour and cognitive functions such as learning, memory, and decision-making (3).
The rise in evidence has unsurprisingly coincided with a sharp increase of ‘gut-friendly’ foods on our supermarket shelves which aim to ‘improve’ the flora of our gut and thus our health overall.
One category which has seen a huge rise are ‘fermented’ food products. From kombucha to kefir and kimchi to sauerkraut, this ever-expanding network of products is set to top a global net worth of £30bn by 2022 (4) . It’s not surprising then that the numbers of new products emerging every month can be overwhelming. But, do they work?
Before I mention these foods and their credibility, it is worth giving an overview of the gut itself, the bacteria within it and how certain fermented foods may influence it.
Our Gut – A brief summary
‘Gut’ is a word given to the entirety of our 9m long digestive tract, beginning at the mouth and finishing at the end of our colon. It’s responsible for ingesting, digesting and assimilating nutrients and vitamins from the foods that we eat effectively to give us energy (from macronutrients) and prevent disease (from vitamins and minerals).
The gut is a particularly unique organ in that it is the only one that can work independently of the brain and central nervous system through its own ‘mini-brain’ known as: the enteric nervous system (ENS). The gut’s ‘mini-brain’ is connected to our central nervous system (brain and spinal-cord combined) via the a critical nerve called the vagus nerve. This creates an ongoing, bidirectional communication path between the two. This relationship has been dubbed the ‘gut-brain axis’. Further to this another communication channel, another that is being explored, is one between our gut flora and the brain known as the ‘microbiota-brain axis’ in which early studies have shown that what and how we feed our gut may affect our mood and behaviours. (5)
Our Gut & Bacteria – The low down
Our gut is also home to trillions of live bacteria, which is as unique to us as our DNA and fingerprint. In recent years these live bacteria have become the subject of increased research and is usually referred to as the ‘gut microbiota’. An overgrowth of bad bacteria in the gut has been linked to depression, disease, skin conditions and auto-immune diseases, so the trick is to keep it in check by feeding the hundreds of different strains of good bacteria, which are responsible for many beneficial processes.
‘How did I develop it, and how can I optimise it?!’
Most of the bacteria found in our gut microbiome is passed onto us during birth from our mothers (6). From here, it evolves and develops to be our microbiome (which is as unique to you as your fingerprint or DNA) within our first 1000 days. This is shaped mainly by our mother’s breast milk, our first solid foods and antibiotic use.
However, after this period, there are many factors that can still affect the balance of your gut microbiome, most notably:
- antibiotic use (7). Studies have shown that antibiotic use decreases the richness and diversity of the good bacteria in our gut, some of which don’t return even past a 6-month period
- shift in diet such as malnutrition, or a serious diet change e.g. keto diet, switching to a plant-based diet from a meat-eating diet (8)
Given that the balance of your gut’s bacteria can be influenced by your diet, retailers are creating products targeted at ‘helping’ the good gut bacteria to thrive. One of these product categories is fermented foods, which aim to encourage the growth of the good bacteria in our gut through live microorganisms called ‘probiotics’. Do a quick sweep of any retailer and you’ll soon see the diverse range of probiotic products on the shelf.
Probiotics have been studied extensively in recent years and have the potential to positively influence the gut microbiota when eaten in the right amounts (9) by:
- increasing the levels of good bacteria within our gut and reducing harmful bacteria (10)
- help the synthesis of nutrients and how well they are used by the body (11)
- reducing toxins and blocking toxin receptors in the body (12)
It is a key point to note here that probiotics will interfere with certain antidepressants known as monoamine oxidase (MAO). Refrain from fermented foods if you are taking this medication.
Fermented Foods – A Natural Probiotic
A fermented food is one that has undergone a biochemical process, breaking down a food to a more digestible one via live yeasts or bacteria, which produces and encourages the growth of beneficial bacteria within the food. This may not sound very appealing, but chances are you have been eating them your whole life.
Some fermented foods such as wine and beer then undergo a step which removes the live bacteria, such as pasteurisation (heat), or filtration. However, other foods such as kefir, kombucha and kimchi leave these live bacteria and yeasts intact, allowing the good bacteria to multiply within it, the living bacteria within these foods are known as ‘probiotics’.
Although fermented foods contain probiotics the research behind whether they have enough to influence your microbiome to such a degree that would make a difference, is still being explored and more research is needed. There are a few key tips when deciding on whether to buy that ‘gut-altering’ product.
Kombucha is one of the most prevalent fermented products to hit the high street. It is made when a specific live culture of bacteria and yeasts, known as a SCOBY, is added to sweetened green or black tea. The live cultures within this feed on the sugar allowing them to multiply and thrive.
The probiotic content of kombucha will vary from brand to brand. Although there is still no evidence for the probiotic benefits of kombucha, it contains several species of lactic-acid bacteria which may have probiotic function (13). When choosing a product make sure you choose one that has not been pasteurised, as this step will kill the live bacteria. Check the sugar content to ensure it’s not too high and aim for live cultures in the billions for maximum effect.
Kimchi & fermented veg:
Fermented vegetables such as Kimchi and sauerkraut are covered in good bacteria naturally. When you slice these vegetables, grate and squeeze them with salt, they ferment, releasing their juices, which mingles with the salt to create a probiotic rich brine. Again, no research has concluded these ancient veggies affect the microbiome but they are probiotic rich.
Based on in vitro and animal studies and preliminary human studies the potential therapeutic actions of kimchi include: Anticancer, anti-obesity and colorectal health promotion amongst others (14). Always check the salt content of these products as they tend to be high. Look for and check the label to ensure they are preserved in water and salt, with low vinegar.
The word “kefir” is derived from the Turkish word “Keif,” which means “good feeling”, alluding to the benefits of those who drink it.
Kefir is a cultured dairy product created when kefir ‘grains’, made from bacteria and yeast are added to milk (for up to 2 weeks) creating a creamy, tart flavour. It is a rich source of probiotics and calcium. This fermented food has slightly more research behind it with one study showing that consuming 200 ml of kefir daily for six weeks decreased markers of inflammation, a known contributor to the development of chronic diseases like heart disease and cancer (15). Kefir may also help enhance bone health. One study looked at the effects of kefir on 40 people with osteoporosis, a condition characterized by weak, porous bones. After six months, the group consuming kefir was found to have improved bone mineral density, compared to a control group (16). When picking this out compare brands and look out for how many strains of bacteria are in each drink (some are up to 16!) and make sure the live bacteria numbers are in the billions.
Tempeh is an Indonesian food made from fermented soybean and in the last couple of years it has been gaining popularity on our supermarket shelves. It is a great source of a complete protein, containing all nine essential amino acids. Although a fermented food, this product needs to be cooked before eating, which kills the live bacteria and so cannot be considered a probiotic. Discount it to help your gut microbiome but it’s a great source of protein and calcium for vegetarians.
- The effect of fermented foods on the human microbiome is still largely unconfirmed and only small trials have been carried out to date
- Read the label and ensure each product is unpasteurised
- Kefir has been slightly more explored, with research showing that 200ml of kefir daily for 6 weeks can reduce inflammation markers
- Eat more fibre, plant based, diverse foods to help our good bacteria to thrive and survive!
(1) Dash Sarah, et al. The gut microbiome and diet in psychiatry: focus on depression. (2015). Available at: https://journals.lww.com/co-psychiatry/Abstract/2015/01000/The_gut_microbiome_and_diet_in_psychiatry___focus.2.aspx
(2) Macpherson AJ, Harris NL. Interactions between commensal intestinal bacteria and the immune system. Nat Rev Immunol. 2004;4:478–485.
(3) Lai, H., Young, J., Lin, C., Chang, C., Lu, C., Martel, J., Ojcius, D. and Ko, Y. (2014). Impact of the gut microbiota, prebiotics, and probiotics on human health and disease. Biomedical Journal, 37(5), p.259.
(4) (Persistence Market Research Pvt. Ltd)
(5) Lai, H., Young, J., Lin, C., Chang, C., Lu, C., Martel, J., Ojcius, D. and Ko, Y. (2014). Impact of the gut microbiota, prebiotics, and probiotics on human health and disease. Biomedical Journal, 37(5), p.259.
(6) Science | AAAS. (2019). Babies get critical gut bacteria from their mother at birth, not from placenta, study suggests. [online] Available at: https://www.sciencemag.org/news/2019/07/bacteria-free-placentas-suggest-babies-pick-microbiome-birth [Accessed 1 Nov. 2019].
(7) Nature.com. (2019). Antibiotics alter the gut microbiome and host health. [online] Available at: https://www.nature.com/articles/d42859-019-00019-x [Accessed 2 Nov. 2019].
(8) David, L., et al. (2013). Diet rapidly and reproducibly alters the human gut microbiome. Nature, [online] 505(7484), pp.559-563. Available at: https://www.nature.com/articles/nature12820 [Accessed 2 Nov. 2019]. Pluznick, J. (2017). Microbial Short-Chain Fatty Acids and Blood Pressure Regulation. Current Hypertension Reports, [online] 19(4). Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5584783/ [Accessed 7 Jul. 2019].
(8) Marchesi et al. (2015) “The gut microbiota and host health: a new clinical frontier”. Gut, [online] 65(2), pp.330-339. Available at: https://gut.bmj.com/content/65/2/330.short [Accessed 7 Jul. 2019].
(9) Pandey et al. (2015) “Probiotics, prebiotics and synbiotics- a review” [accessed 2 Nov. 2019] 2019 via: https://www.ncbi.nlm.nih.gov/pubmed/26604335]
(10) Sanches et al. (2016) “Probiotics, gut microbiota, and their influence on host health and disease” [accessed 2 Nov. 2019] via: https://onlinelibrary.wiley.com/doi/full/10.1002/mnfr.201600240]
(11) Sanches et al. (2016) “Probiotics, gut microbiota, and their influence on host health and disease” [accessed 2 Nov. 2019] via: https://onlinelibrary.wiley.com/doi/full/10.1002/mnfr.201600240]
(12) Sanches et al. (2016) “Probiotics, gut microbiota, and their influence on host health and disease” [accessed 2 Nov. 2019] via: https://onlinelibrary.wiley.com/doi/full/10.1002/mnfr.201600240]
(13) Marsh, Alan J, et al. “Sequence-Based Analysis of the Bacterial and Fungal Compositions of Multiple Kombucha (Tea Fungus) Samples.” Food Microbiology, vol. 38, 2014, pp. 171–8, www.ncbi.nlm.nih.gov/pubmed/24290641, 10.1016/j.fm.2013.09.003. Accessed 4 Nov. 2019.
(14) Lai, H., Young, J., Lin, C., Chang, C., Lu, C., Martel, J., Ojcius, D. and Ko, Y. (2014). Impact of the gut microbiota, prebiotics, and probiotics on human health and disease. Biomedical Journal, 37(5), p.259.
(15) ADİLOĞLU, A., GÖNÜLATEŞ, N., İŞLER, M. and ŞENOL, A. (2013). The Effect of Kefir Consumption on Human Immune System: A Cytokine Study. Mikrobiyoloji Bulteni, 47(2), pp.273-281.
(16) ADİLOĞLU, A., GÖNÜLATEŞ, N., İŞLER, M. and ŞENOL, A. (2013). The Effect of Kefir Consumption on Human Immune System: A Cytokine Study. Mikrobiyoloji Bulteni, 47(2), pp.273-281.