PUBLIC HEALTH added to them, as most of the natural probiotics found in yoghurt products die during processing. Commercial probiotic supplements are also available in the form of powders, tablets and liquids. Some fermented foods are natural sources of probiotics too, such as kefir (a fermented milk). So, where to start? Currently, there is no form of probiotic that has been proven to work better than others. What is important in commercial products, however, is that the particular strains have the correct encapsulation to survive transit through our gut. This is strain specific.1 Most probiotics are bacterial, however, other microbes (e.g. yeast, fungi and viruses) also make up the human microbiota.7 Probiotics are named by their genus, then species and finally their strain. The most commonly proposed organisms are Lactobacillus and Bifidobacterium strains. PREBIOTICS
What about prebiotics? Confused? Prebiotics are described as non-digestible, fermentable food components that result in the selective stimulation of growth and activity of one or a limited number of microbial genera/species in the GI microbiota that provide health benefits to the host.8 Prebiotics are resistant to digestion in the upper GI tract and are fermented by the gut microbiota. This in turn impacts on the growth and activity of specific bacteria. For those familiar with the low FODMAP diet, the term prebiotics may be ringing bells. This is because the most common classes of prebiotics are also FODMAPs – fructans (oligofructose, fructo-oligosaccharides) and galactans (galactooligosaccharides). Therefore, those following a low FODMAP diet for the management of IBS are in fact restricting prebiotics during the elimination phase of the diet. THE EVIDENCE
There are many conditions to which probiotics are thought to have a benefit, from a wide range of GI disorders and diarrhoea to conditions such as allergies, dental caries and vaginosis.1 However, proven evidence for the use of probiotics remains lacking. There are only a few conditions to which the use of probiotics has been proven to be beneficial, including the following: 9-12
• • • •
Acute onset of infectious diarrhoea Antibiotic-associated diarrhoea The prevention of traveller’s diarrhoea The prevention of clostridium difficile (C. diff) associated diarrhoea • Helicobacter pylori eradication (as an additional therapy) • The prevention of pouchitis Despite the studies supporting the use of probiotics for these conditions, varying studies provide different outcomes, with results differing depending, for example, on the specific strain or the duration they are taken. For IBS-D specifically, it is thought that a multistrain probiotic is best associated with significant improvement in symptoms in IBS-D patients and is well-tolerated.13 Results from this particular study indicate that probiotic supplementation confers a benefit in IBS-D and deserves further investigation. Currently, probiotics are not recommended when following a low FODMAP diet. However, a study by Staudacher et al14 concluded that probiotics in combination with a low FODMAP diet improve the effects of Bifidobacteria abundance and stool acetate. The study also notes that more research is needed on the effect of the reintroduction of FODMAPs on the gut microbiota before a low FODMAP diet and probiotic therapy can be advised conjunctively. Research on both live and bio yoghurts has also been unclear. For example, two different studies looking at probiotics and the prevention of antibiotic-associated diarrhoea have provided conflicting results. Conway et al demonstrated no benefit from taking standard or bio yoghurts, whereas Beniwal et al showed a reduction in the incidence of antibiotic-associated diarrhoea when yoghurts were introduced.15,16 A number of studies have looked at the effects of prebiotics on GI disorders. Randomised control trials looking at the effect of prebiotics on various diarrhoea-associated conditions concluded that prebiotics had no impact on the duration of antibiotic-associated diarrhoea, however, they may reduce the relapse rate of C. diff patients or reduce the incidence of traveller’s diarrhoea. These studies typically used placebo groups and an addition of a certain number of prebiotics to the diet per day.17-19 www.NHDmag.com October 2018 - Issue 138
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