Probiotics and prebiotics

What are probiotics?

Probiotics are defined as "live micro-organisms that confer a health benefit on the host when administered in adequate amounts." The major source of probiotics for humans is dairy-based foods containing intestinal species of Lactobacillus or Bifidobacterium. The most common type used is Lactobacillus acidophilus (also known as one of the "friendly bacteria"), a species of Gram-positive, rod-shaped bacteria often found in the intestinal tract of humans and animals, the human mouth and vagina. It is an anaerobic organism that produces lactic acid which reduces the pH. This may have an inhibitory effect on other organisms, especially candida. The yeast Saccharomyces cerevisiae and some Escherichia coli and Bacillus species are also used as probiotics.

What are prebiotics?

Prebiotics are defined scientifically as "selectively fermented ingredients that result in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health." They are non-digestible carbohydrates (mainly oligosaccharides and non-starch polysaccharides) which act by promoting the growth and/or activity of probiotic bacteria in the gut. The most common are fructo-oligosaccharides (FOS), inulin and galacto-oligosaccharides. They are found in various vegetables and fruit such as tomatoes, onions, garlic, leeks, asparagus and bananas. Prebiotics are relatively stable and, unlike probiotics, can be relied on to arrive relatively unchanged in the gut despite the presence of digestive enzymes.

What are synbiotics?

Synbiotics contain prebiotics and probiotics in the same preparation.

Possible uses of probiotics

Many commercially available products (eg, yoghurt) are classed as foodstuffs. This means that they escape the rigorous testing for efficacy which is applied to medicines. They have biologically plausible modes of potential action as displacers of pathogens, immunomodulators or local antimicrobial agent secretors. Initial scientific investigation indicates some evidence of usefulness of probiotics in some areas and a definite impetus to continue research into their effects. Doses and recommendations/guidelines for their routine use, however, have yet to be established, pending ongoing research findings. Most benefit has been demonstrated, naturally, for gastrointestinal disorders.

Gastrointestinal disorders

• Prophylaxis of antibiotic-associated diarrhoea. Studies vary, and ongoing research into the dose of probiotics continues, but there is evidence that probiotics may prevent some antibiotic-associated diarrhoea. ^{1 2}

• Prevention of traveller's diarrhoea. ³

• Prevention of Clostridium difficile diarrhoea. There is evidence of moderate certainty that probiotics are safe and effective in preventing C. difficile diarrhoea.⁴ Public Health England guidelines on C. difficile management, however, do not yet recommend their routine use ⁵

• There has been interest in the use of probiotics to induce remission in inflammatory bowel disease and to treat pouchitis, but there is very little evidence for their benefit for these indications. ^{6 7 8}

• Irritable bowel syndrome (IBS). There is some evidence that probiotics may improve symptoms of IBS, although ongoing studies are needed to identify which patients benefit, and optimal regimens. ^{9 10} The National Institute for Health and Care Excellence (NICE) recommends that if patients wish to try probiotics they should take them at a dose recommended by the manufacturer for a minimum of four weeks. ¹¹ The more recent BSG guidelines suggest that they might be tried for up to 12 weeks, but agree with NICE that it is not possible to recommend a specific type of probiotic. ¹²

• Eradication of Helicobacter pylori. A meta-analysis concluded that fermented milk-based probiotic preparations increased eradication rates in patients on standard eradication therapy by 5-15%.^{13 14}

• Necrotising enterocolitis. There is only low to moderate certainty for the benefits of probiotic therapy for treating this condition in premature babies. ¹⁵

Other possible uses

Many studies are ongoing into the possible benefits of probiotics in areas including:

• Infantile colic.

• Bacterial vaginosis.

• Vulvovaginal candidiasis.

• Prevention of preterm labour.

• Prevention of recurrent urinary tract infections.

• Prevention of infant eczema. There is limited evidence for the use of probiotics in children with eczema, or by women who are breastfeeding infants with eczema. ¹⁶

• Allergic rhinitis. ^{17 18}

• Fibromyalgia - there is some evidence for a reduction in symptoms, but further large studies are needed to confirm this.^{19 20}

• Treatment of non-alcoholic fatty liver disease and non-alcoholic steatohepatitis. ^{21 22}

• Hepatic encephalopathy, where there is some evidence for the use of probiotics. ²³

• Reduction of risk of cardiovascular disease in those with type two diabetes. ²⁴

There is some evidence that probiotics can affect immune response, and therefore could have potential benefit in any number of clinical scenarios.^{25 26}

Possible uses of prebiotics and synbiotics ¹⁰

There is much interest in the potential for use of prebiotics and synbiotics. Research is being undertaken to look at possible benefit for an enormous number of areas, including:

• Immune response. There is some evidence that prebiotics in combination with probiotics may boost the immune response.²⁷

• Obesity.^{28 29}

• Type 2 diabetes mellitus.³⁰

Cautions

Evidence suggests probiotics are safe in the vast majority. However, there is a small risk of adverse effects, such as sepsis. It is therefore recommended that use of these agents be avoided in those who are immunocompromised, severely debilitated, critically ill or postoperative, as this population is most at risk.³¹ There are differences between probiotic/prebiotic agents and regimens both within clinical trials and the way they are used, and these are not likely to be equivalent. Therefore, there is much work to be done before specific clinical guidelines and recommendations can be made.

Meanwhile probiotics and prebiotics exist in everyday food products on supermarket shelves, as well as in capsules, powders and sachets, from a bewildering array of sources. As doctors, we are not yet in a position to give specific evidence-based advice on exactly which product patients should take in which situation.

Future research

There is no doubt that prebiotics and probiotics are an interesting group that warrants further investigation. Guidelines were produced in 2010 to guide ongoing research.³² Studies on one strain of micro-organism cannot be assumed to apply to others, and experimental studies have often not been extended to humans. Many brands of commercially produced probiotics and prebiotics exist, which are not standardised, and there is concern about the applicability of meta-analyses which extend to such heterogeneous groups of subjects, conditions and treatments. The reader should note that this is a fast developing area and new research is published regularly.