A Body of Evidence

OUR digestive health is in part dependent on a microscopic battle for supremacy. It's almost a case of 'no guts, no glory' when it comes to the estimated 100 trillion beneficial microorganisms, or probiotics, representing more than 500 different species that inhabit every normal, healthy bowel. That's because at any time – with the wrong sort of food or lack of it, allergens, medication or even a change in environment – pathogenic microorganisms that co-exist in the complex ecology of the human gastrointestinal system.

Probiotics, which may occur naturally in foods such as yoghurt, kefir, cheese, soy sauce and other fermented foods, are intended to confer a health benefit when consumed. These gut-dwelling microflora keep pathogens in check, aid digestion and nutrient absorption, and contribute to immune function. Probiotics are also found in dietary supplements, dairy beverages and bakery products, which are formulated with potentially beneficial bacteria or yeast.

Current clinical studies and meta-analyses suggest that probiotic therapy can help treat several gastrointestinal ills, including the most recent that suggest that probiotics can stem diarrhoea in nutrient-deficient children and antibiotic-associated diarrhoea in adults.

Overcoming adverse effects of antibiotics
Antibiotics are intended to destroy pathogenic bacteria, but diarrhoea is a common adverse effect of such medications and afflicts as many as 30% of patients. This is because the use of antibiotics can disturb the gastrointestinal flora – more simply antibiotics disturb the natural balance of "good" and "bad" bacteria in the intestinal tract causing harmful bacteria to multiply beyond their normal numbers – and lead to antibiotic associated diarrhoea (AAD).

Consumption of probiotics can reduce the risk of diarrhoea caused by taking antibiotics by restoring the natural balance of bacteria, according to a recent review published in JAMA1. This potential to maintain or restore microbial ecology during or after antibiotic treatment is substantiated by results of the randomised controlled trials. "There is an increasing interest in probiotic interventions, and evidence for the effectiveness of probiotics in preventing or treating AAD is also increasing," the authors write.

Susanne Hempel, Ph.D. of RAND Health and colleagues conducted the metaanalyses to evaluate the available evidence on probiotic use for the prevention or treatment of AAD. Their review found sufficient evidence to conclude that adjunct probiotic administration is associated with a reduced risk of AAD. The majority of the trials used Lactobacillus-based interventions alone or in combination with other probiotics. Across 63 trials that reported the number of participants, including adults and children, probiotic use was associated with a 42% lower risk of developing diarrhoea compared with a control group not using probiotics.

An earlier review[2] of 16 studies by Johnston et al. point to the same evidence. The studies tested 3,432 children (2weeks to 17 years of age) who were receiving probiotics co-administered with antibiotics to prevent AAD. Analyses showed probiotics (Lactobacilli spp., Bifidobacterium spp., Streptococcus spp., or Saccharomyces boulardii alone or in combination) were generally well tolerated, and minor side effects occurred infrequently, with no significant difference between probiotic and control groups receiving placebos or other treatments thought to prevent AAD. The data reviewed suggest that L. rhamnosus and S. boulardii at a high dosage of 5 to 40 billion CFU/day may prevent the onset of ADD, with no serious side effects documented in otherwise healthy children. This benefit for high-dose probiotics needs to be confirAir Max