Prebiotics are non-digestible compounds that lead to favourable changes in the intestinal microbiota, and synbiotics are defined as products that contain both probiotics and prebiotics.²  

Probiotics may mediate health effects through one or more of several identified mechanisms that affect the intestinal ecosystem, which can lead to the antagonism of potential pathogens, an improved intestinal environment, bolstering of the intestinal barrier, down-regulation of inflammation, and up-regulation of the immune response to antigenic challenges. These mechanisms:³  

1. Have an impact on mucosal immune responses.
2. Interact with commensal or potential pathogenic microbes.
3. Generate  metabolic end products such as short-chain fatty acids.
4. Communicate with host cells  through chemical signalling.

The use of bacteriotherapy dates back to 4th century China, which was used to treat patients suffering from food poisoning and severe diarrhoea. More modern history acknowledges Russian scientist and Nobel laureate, Prof Elie Metchnikoff, as the leading figure in the conceptualisation of probiotic use in medicine.^5,6

 He postulated that lactic acid bacteria offer health benefits that can promote longevity. According to his theory, ‘intestinal auto-intoxication’ and resultant ageing could be suppressed by modifying the gut microbiota and replacing proteolytic microbes responsible for producing toxic substances (eg phenols, indoles, and ammonia from the digestion of proteins) with saccharolytic microbes.²   

Over the last two decades, probiotics have become increasingly popular during as a result of the continuously expanding scientific evidence pointing to their beneficial effects on human health. Thousands of studies have investigated the potential benefits of probiotics on gut, vaginal, and skin health.^1,3,4,7 

Not all probiotics are created equally, cautions statuary bodies 

However, the American National Centre for Complementary and Integrative Health (NCCIH) and the World Gastroenterology Organisation (WGO) caution that all probiotics are not created equally.^3,4  

According to the NCCIH, different types of probiotics may have different effects. For example, if a specific kind of Lactobacillus helps prevent a condition or disease, that doesn’t necessarily mean that another kind of Lactobacillus-containing probiotics would do the same thing.^1,2 

According to the authors of the 2023 WGO Global Guidelines on Probiotics and Prebiotics ‘the quality of probiotic products depends on the manufacturer concerned. Since most are not made to pharmaceutical standards, regulatory authorities may not oversee adherence to quality standards’.³  

Important factors that need to be taken into consideration when recommending a probiotic include:³  

• Assurance of potency (maintenance of viability, typically indicated by colony-forming units, through the end of shelf-life) 
• Purity (manufacturing processes that sufficiently reduce any pathogens of concern) 
• Identity (current nomenclature used to specify the genus, species, and subspecies, if applicable, and a strain designation for each strain in the product). 

Purchasing products from reliable manufacturers is therefore essential, stress the guideline authors.³ 

What are probiotics good for? 

The WGO guidelines reviewed the evidence of the health benefits of probiotics and this is what they found:³  

Diarrhoea treatment and prevention

Treatment of acute diarrhoea 

Some probiotic strains are useful in reducing the severity and duration of acute infectious diarrhoea in children. Oral administration shortens the duration of acute diarrheal illness in children by about a day.  

Prevention of acute diarrhoea 

There is evidence that certain probiotics can be effective in some specific settings. A Cochrane meta-analysis found that early administration of probiotics is needed and has no benefit in diarrhoea lasting 48 hours or longer. 

Prevention of antibiotic-associated diarrhoea 

There is evidence of efficacy in adults or children who are receiving antibiotic therapy. Meta-analyses concluded that probiotics may provide a moderate effect in preventing antibiotic-associated diarrhoea in children, adults, and elderly adults. 

Prevention of C. difficile diarrhoea 

A 2017 meta-analysis concluded with moderate certainty that probiotics are effective in preventing Clostridium difficile–associated diarrhoea in patients receiving antibiotics. Probiotic use in patients who are not immune-compromised or severely debilitated appeared to be safe. 

Prevention of radiation-induced diarrhoea 

A 2013 meta-analysis concluded that probiotics may be beneficial in the prevention and possibly in the treatment of radiation-induced diarrhoea. 

H. pylori eradication

The 2022 Maastricht VI/Florence Consensus Report on the management of helicobacter pylori infection concluded that certain probiotics have been shown to be effective in reducing gastrointestinal side effects caused by H. pylori eradication therapies and thus have a beneficial effect on the treatment. However, there is no evidence to support the concept that a probiotic alone, without concomitant antibiotic therapy, would be effective. Instead, probiotics appear to increase the H. pylori eradication rate by reducing side effects related to eradication therapy, rather than through direct effects on H. pylori. 

Hepatic encephalopathy prevention and treatment 

A 2017 Cochrane meta-analysis found that evidence from three studies on the benefits of probiotics for people with hepatic encephalopathy was of low quality. Although no difference in the mortality rate was observed, the authors concluded that probiotics may improve recovery, quality of life, and plasma ammonia concentrations. 

Immune response 

Evidence suggests that several probiotic strains and the prebiotic oligofructose are useful in improving the immune response. Evidence suggestive of enhanced immune responses has been obtained in studies aimed at preventing acute infectious disease (nosocomial diarrhoea in children, influenza episodes in winter) and in studies that tested antibody responses to vaccines. 

Inflammatory bowel disease  

Pouchitis 

There is evidence for the usefulness of a probiotic mix in preventing an initial attack of pouchitis and in preventing further relapse after the induction of remission with antibiotics. The probiotic mix is recommended for adults and children with pouchitis of mild activity, or as maintenance therapy for those in remission. 

Crohn’s disease 

Studies of probiotics have indicated that there is no evidence to suggest that they are beneficial for the induction or maintenance of remission.  

Irritable bowel syndrome  

A reduction in abdominal bloating and flatulence as a result of probiotic treatments is a consistent finding in published studies. Some strains may ameliorate pain and provide global relief. The literature suggests that certain probiotics may alleviate symptoms and improve the quality of life in persons with functional abdominal pain.  

Colic 

 Lacticaseibacillus casei has been shown to reduce crying time in breastfed infants with colic. 

Lactose malabsorption 

Streptococcus thermophilus and Lactobacillus improve lactose digestion and reduce symptoms related to lactose intolerance. This was confirmed in a number of controlled studies with individuals consuming yogurt with live cultures. 

Necrotising enterocolitis 

Probiotic supplementation reduces the risk of necrotising enterocolitis in preterm neonates. Meta-analyses of randomised controlled trials have also shown a reduced risk of death in probiotic-treated groups, although not all probiotic preparations tested are effective. The number needed to treat to prevent one death from all causes by treatment with probiotics is 20. Special attention to adequate quality in the probiotic product is important for this vulnerable group of patients. There was moderate certainty for the reduction of the mortality rate and late-onset invasive infection, but no effect was observed on severe neurodevelopmental impairment. 

Non-alcoholic fatty liver disease 

The usefulness of certain probiotics as a treatment option to mitigate steatohepatitis has been proven through a number of randomized clinical trials in adults and children. Probiotics provided improvements in the outcomes of homeostasis model assessment, blood cholesterol, tumour necrotising factor-α, and liver function tests. Further studies are needed to confirm long-term benefits. 

Prevention of systemic infections 

Probiotics and prebiotics have been shown to affect several clinical outcomes that are outside the normal spectrum of gastrointestinal disease. Emerging evidence suggests that gut microbiota may affect several non-gastrointestinal conditions, thereby establishing a link between these conditions and the gastrointestinal tract. Numerous studies have shown that probiotics can reduce bacterial vaginosis, prevent atopic dermatitis in infants, reduce oral pathogens and dental caries, and reduce the incidence and duration of common upper respiratory tract infections. The net benefit of probiotics during the perinatal period in preventing allergic disease has led to a World Allergy Organization recommendation on probiotic use during pregnancy, breastfeeding, and weaning in families with a high risk of allergic disease. Probiotics and prebiotics are also being tested for the prevention of some manifestations of metabolic syndrome including excess weight, type 2 diabetes, and dyslipidaemia. 

References   

1. França K. Topical Probiotics in Dermatological Therapy and Skincare: A Concise Review. Dermatol Ther (Heidelb), 2021. 
2. Patel R, DuPont HL. New approaches for bacteriotherapy: prebiotics, new-generation probiotics, and synbiotics. Clin Infect Dis, 2015. 
3. Guarner F,  Sanders ME, Szajewska H et al. 2023 World Gastroenterology Organisation Global Guidelines Probiotics and Prebiotics. [Internet]. Available from: https://www.worldgastroenterology.org/UserFiles/file/guidelines/probiotics-and-prebiotics-english-2023.pdf 
4. NCCIH. Probiotics: What You Need To Know. [Internet]. Available from: https://www.nccih.nih.gov/health/probiotics-what-you-need-to-know 
5. Te Haar S. History of probiotics . [Internet]. Available from: https://www.optibacprobiotics.com/learning-lab/about/probiotics/history-of-probiotics#:~:text=What%20Metchnikoff%20discovered%20was%20that,health%20and%20increased%20their%20lifespan 
6. Tungland B. Chapter 9 - Dysbiosis of the Microbiota: Therapeutic Strategies Utilizing Dietary Modification, Pro- and Prebiotics and Fecal Transplant Therapies in Promoting Normal Balance and Local GI Functions. Human Microbiota in Health and Disease, Academic Press, 2018, Pages 381-419.  
7. Lehtoranta L, Ala-Jaakkola R, Laitila A, Maukonen J. Healthy Vaginal Microbiota and Influence of Probiotics Across the Female Life Span. Front Microbiol, 2022.