What Do We Know About Probiotics?

Article by Julia Breden


The recent increased focus on the gut microbiome is more than just a trend and is among the most popular topics of research due to its central role in so many of the body’s functions and impact on our physical and mental health. Part of this research includes the use of probiotics and prebiotics, both of which have been shown to be significant in developing and sustaining a healthy gut microbiome. 

Probiotics vs prebiotics

Probiotics are a mixture of live bacteria and yeasts involved in restoring and supporting the balance of bacteria, and prebiotics are specialised plant fibres that feed these probiotics (1). They both exist in a number of foods and drinks and can also be obtained in supplement form but, with the ever-expanding information available in relation to gut health and probiotics available, knowing where to start can be confusing. 

This article will discuss the gut microbiome and its connection to the brain, nutrition, and prebiotics and probiotics and how they can be implemented within diet, as well as in supplement form. 

What is the gut microbiome and gut bacteria? 

The gastrointestinal tract is home to the gut microbiome which comprises a complex population of microorganisms, most abundant within the small and large intestines as well as the colon, which is made up predominantly by bacteria and yeasts, along with fungi, archaea, and viruses (2). Trillions of strains, and thousands of species of bacteria exist and are often perceived negatively, however not all bacteria are equal; where types involved in illness would be considered ‘bad’ bacteria, and ‘good’ bacteria are those that aid in promoting gut health. Probiotic bacteria are ‘good bacteria’, and extensive evidence shows their wide and diverse range of effects throughout the body, influencing both physical and mental health (3). 

The benefits of their consumption include restoring and balancing good bacteria in the microbiome, reducing inflammation, increasing nutrient absorption, improving digestion and bowel habit problems, and have been seen to benefit many gut disorders such as irritable bowel syndrome (IBS). IBS, which is one of the most common, incurs symptoms like disrupted bowel habits, bloating, and stomach pains, all of which can be worsened by lifestyle habits or foods, many being high fibre, prebiotic, and dairy foods therefore complicating gut health improvement (4). 

 Similar symptoms are also* seen in conditions such as Small Intestinal Bacterial Overgrowth (SIBO), which involves an abnormal increase in bacteria (5), and Leaky Gut syndrome which is characterised by damage to the intestinal barrier. This barrier protects the gut microbiome, aids nutrient absorption, and reduces gut inflammation, so its impairment can lead to bowel dysfunction, nutritional deficiencies, and a decline in energy and cognitive function.

Studies on the efficacy of probiotics in improving these conditions have shown predominantly positive results that have also enabled wider health advantages, such as those relating to cardiovascular disease, type 2 diabetes and other diseases which could have significant future impacts, however results are mixed due to varying factors and require further study (6). Research involved their key role in immune health due to the close relationship between the immune system and the gut, where it is thought that over 70% of it is located (7); The Bifidobacterium and Lactobacillus strains, which are perhaps most commonly known due to their abundance in supplements and food sources and many advantages including producing health-essential B vitamins, are highlighted as the most supportive to immune health through fighting off harmful bacteria and enhancing immune cell function (1). Evidence for the influence of the gut on wider health-impacts, such as cardiovascular diseases is also being researched 

The primary role of probiotic bacteria is the process of fermenting partly or fully non-digestible prebiotic resistant-starches and fibres which facilitates production of short chain fatty acids (SCFA) that have many important functions including supporting intestinal cells and the intestinal barrier (8). Bacterial species produce vitamin K as well as B vitamins, of which they also require alongside others such as vitamins A, C, D, and E (9), as well as omega-3 fatty polyunsaturated fatty acids which have been shown to enhance the probiotic population and GM and cognitive function (10).

The ‘Gut-Brain Axis’

It is now more commonly known that the gut is linked to our mood through its connection to the brain; Probiotics support the large network of bacteria that maintain a unique relationship with our bodies and support communication between the gut and central nervous system, commonly known as the ‘Gut Brain Axis’. As well as impacting intestinal and cognitive function, it is central to many roles within the body including the metabolic, endocrine, and immune systems, consequently influencing many aspects of our health and affects cognitive health, mood, and the development of psychological disorders such as anxiety and depression (11). 

Furthermore, studies have highlighted the involvement of bacterial species in the production of neurotransmitters including serotonin (often described as our ‘happy hormone’); Inflammation and bacterial imbalance disrupt its production in the gut, of which is thought to be highly proportionate (12), however the diversity of information causes much speculation about the accuracy of this.

A variety of internal factors, like psychological stress, and external factors, including antibiotic use, and poor activity, sleep, and diet, are linked to microbiome and gut-brain axis disturbances and further consequences (13). The essential support provided by probiotics highlights the importance of their consumption for good health and mood, of which studies show can be achieved through healthy, prebiotic and probiotic-rich diets or probiotic supplements (14). 

Probiotic sources and the role of nutrition 

Probiotics can be consumed through diet or supplements, however, it is generally advised that diet, as opposed to supplements, is both more effective and preferable, especially when generally healthy (15)(12). For some, such as those with particularly poor gut health, supplementing may be optimal due to high dosages or convenience, however, caution may be required for others, such those with an increased risk of illness (16). It is important to obtain professional advice before consuming supplements and consider key factors such as their quality, ingredients, number and variation of species and strains, and absorption. 

Probiotic foods are those with naturally occurring or added probiotic bacteria known as ‘live cultures’, and yeasts, which are found naturally in foods that have undergone the fermentation process of chemical breakdown by bacteria or yeasts (17). Increasing popularity of both prebiotic and probiotic foods means that they are now more favourable in relation to accessibility, affordability, and diversity as there are now more variations and flavours of these products and more information on ways to incorporate them into your diet as well as how to prepare, eat and make them at home. The significance of their impact requires further study; however, they are still great additions to the diet.

Good sources include:

  • Yoghurt - Only those that include ‘live’ or ‘active cultures’ are probiotic; this will be listed on the label and can now also be found in non-dairy yoghurts. 

  • Kefir - A fermented milk product which can be found in kefir drink and yoghurt products and can also be made at home.

  • Some cheeses - Mainly aged cheeses due to their production process and include aged cheddar, parmesan, edam, and swiss cheese.

  • Sauerkraut - Fermented sliced cabbage with additional seasoning which can be made at home.

  • Kimchi - Fermented vegetables in a spicy seasoning. Traditional kimchi includes cabbage, carrot, and radish although there are now multiple variations and can also be made at home. 

  • Tempeh - Similar to tofu in taste, texture, and appearance, it is also made from soybeans, however tempeh uses the whole soybean in a fermentation process.

  • Miso - A Japanese seasoning product also produced from fermented soybeans, used in paste-form such as in sauces, soups, and dressings.

  • Kombucha - A fermented black tea drink, usually sweetened. Can be bought or homemade in a variation of flavours.

Foods high in fibre, especially those containing prebiotic plant fibres are also highly beneficial and crucial for probiotic bacteria. 

These include: (18)

  • Vegetables

  • Fruits

  • Beans and legumes

  • Oats

  • Wholegrains

  • Nuts and seeds

  • Onions 

  • Garlic

  • Chicory root

Polyphenols, also gaining popularity, are compounds with antioxidant, inflammatory, and prebiotic properties that feed probiotic bacteria.

They’re in many of our favourite foods and drinks including:  (19)

  • Berries

  • Beans

  • Cacao

  • Coffee and tea

  • Olives

  • Herbs and spices


How much do I need?

Including a wide range of healthy foods is vital in gaining a variety of nutrients and their health benefits, particularly soluble and insoluble dietary fibre, so a healthy intake of fruits, vegetables, and wholegrains, many of which are prebiotic, is therefore recommended (20). Mindfulness around purchasing and consuming food products marketed as ‘gut healthy’ is also advocated because, despite their potential benefits, they’re often low in quality and nutrients and involve high amounts of processing, added sugars, saturated fats, and adverse ingredients (20). Foods with these properties can damage gut health by diminishing bacterial diversity and causing inflammation; limiting these foods can be advantageous (21), as well as those that induce digestive problems, or intolerance and allergy symptoms, of which probiotics have also been to improve (22). 

Summary

In summary, improving gut health has a wide range of physical and mental health advantages. Although some individuals may benefit from probiotic supplements, this can be accomplished, for most, through a diet that is varied and rich in nutrients, probiotics, and prebiotics, alongside healthy lifestyle habits that include good sleep hygiene and regular exercise. Furthermore, it is important to be aware that there is much misinformation around the topic of gut health, including the accuracy of research results, some of which will be used as health claims to market products and supplements. The quality and quantity of these will vary so caution in their purchase and consumption is advised, and as mentioned if you’re experiencing gut health concerns then it’s always encouraged to speak with a qualified healthcare professional.


This blog post was written by Julia Breden, who is currently in her third year of studying a Nutrition BSc, specialising in public health at the University of Brighton. She believes health should be an enjoyable part of life in a way that works individually, and that aiding understanding of the wealth of available health information, including misinformation and ‘diet myths’ is key. Julia is also passionate about how nutrition impacts our gut, as well as our brain and behaviour and how our relationship with food affects our food choices. You can find her on Instagram @juliaxb_

References:

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(4) Zhang, T., Zhang, C., Zhang, J., Sun, F. and Duan, L., (2022). Efficacy of probiotics for irritable bowel syndrome: a systematic review and network meta-analysis. Frontiers in Cellular and Infection Microbiology, 12.

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