Abstract

The human diet is integral part of overall health, and human response to foods and their components is often dependent on their dynamic interrelationship with microbes residing in the oral and gastrointestinal tract. Part of this dynamic relationship arises from the ability of bacteria to metabolize dietary components. This microbial involvement can alter the nutritional value of food components by generating specific compound(s) that are formed by gut bacteria. Thus, microbial metabolites may have a positive or negative influence on the risk of multiple diseases, including cancer. Soybeans were selected for this review, because there is considerable worldwide consumption and have been linked as cancer risk modifiers. Considerable evidence indicates that these soy foods are involved with cancer prevention, yet there is considerable variability in the response in terms of cancer risk and tumor behavior. Equol, an active metabolite of the soy isoflavone daidzein has been intensely studied in the last 25 years for its potential health benefits, not just for its estrogenic or anti-estrogenic activities but also for its antioxidant, anti-inflammatory or neuroprotective properties. The aim of this review is to assess the strengths of evidence that links microbially generated metabolite equol from soy foods with cancer risk and tumor behavior. Through a systematic analysis of existing evidence, the review focuses on biological consequences of soyderived equol on cancer-related processes as a function of the amount and duration of exposure, and when possible, human genetics and tissue specificity. While this evaluation specifically focuses on soy, the findings may also serve as a proof-of-principle for examination of food/disease/microbiome relationship with other foods.

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