This paper addresses the use of systematic review and meta-analysis to evaluate the strength of evidence for health benefits of probiotic foods, especially relating to health claim substantiation in the European Union. A systematic review is a protocol-driven, transparent and replicable approach, widely accepted in a number of scientific fields, and used by many policy-setting organizations to evaluate the strength of evidence to answer a focused research question. Many systematic reviews have been published on the broad category of probiotics for many different outcomes. Some of these reviews have been criticized for including poor quality studies, pooling heterogeneous study results, and not considering publication bias. Well-designed and -conducted systematic reviews should address such issues. Systematic reviews of probiotics have an additional challenge - rarely addressed in published reviews - in that there must be a scientifically sound basis for combining evidence on different strains, species or genera. The European Food Safety Authority (EFSA) is increasingly adopting the systematic review methodology. It remains to be seen how health claims supported by systematic reviews are evaluated within the EFSA approval process. The EFSA Panel on Dietetic Products, Nutrition and Allergies deems randomized trials to be the best approach to generating evidence about the effects of foods on health outcomes. They also acknowledge that systematic reviews (with or without meta-analyses) are the best approach to assess the totality of the evidence. It is reasonable to use these well-established methods to assess objectively the strength of evidence for a probiotic health claim. Use of the methods to combine results on more than a single strain or defined blend of strains will require a rationale that the different probiotics are substantively similar, either in identity or in their mode of action.
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