“Polyphenols are secondary plant compounds present in plant based foods. More than 500 different molecular structures in plant foods have been identified and therefore they are a very heterogeneous group of compounds. The most interesting group of polyphenols are flavonoids, as they are found in a wide range of plant foods", explains the epidemiologist. This subgroup can be divided into different classes: Flavonols, flavanones, flavanones, flavones, anthocyanins and isoflavones. "We know from studies in animal models or cell cultures that polyphenols have antioxidant, anti-inflammatory, neuroprotective and anticancerogenic properties." However, the exact mechanisms of polyphenols in the human body are still largely unknown. It is currently assumed that the products of the human metabolism (metabolites) are relevant for possible health effects. “It is difficult to detect significant associations between polyphenol metabolites and endpoints in the human metabolism like cancer or diabetes, because the existing studies are very different. They differ in the investigated polyphenol metabolite or in the endpoint. In some cases, there are too few studies to make specific statements about the association of a particular metabolite with the prevention of chronic diseases", said Rienks.
For her research, Rienks particularly studied isoflavones. Isoflavones are mainly found in soy and soy products. People in Asian countries have the highest intake of isoflavones. “However, the intake in the western countries is underestimated, as convenience foods often contain soy protein or soy flour. The associations of isoflavones varies and depends on the individual isoflavones and their metabolites", explains Rienks. The main isoflavones are daidzein, genistein and glycitein. These can be metabolised by the gut microbiota into metabolites and detected as biomarkers in the blood or urine. As part of her doctoral thesis, the scientist has already published two meta-analyses. “For our analyses, we focused on observational studies investigating isoflavone biomarkers. From our point of view, biomarkers are the better data basis for determining the isoflavone intake of a person. Food frequency questionnaires, which are used in epidemiological studies to measure dietary habits, are not designed to accurately reflect polyphenol intake. The main problem is that dietary assessment methods rely on the self-report of participants. And in addition food composition tables are incomplete."
Her analyses showed that higher concentrations of daidzein and genistein in blood and urine are associated with a lower risk of breast cancer and diabetes. Rienks emphasizes that in order to draw any conclusions we first need more evidence. So further studies at the biomarker level are necessary.
Text: Dr. Maike Gutmann, DGE (TA6)