Association between dietary inflammatory or oxidative stress indices and biomarkers in cardiometabolic and related conditions: A systematic literature review

Inflammation and oxidative stress contribute to the progression of chronic diseases, and the volume of research in this area is rapidly expanding. Various dietary indices have been developed to determine the overall inflammatory or oxidative stress potential of a diet; however, few have been validated in cardiometabolic disease populations. This review aimed to explore the association between dietary indices and biomarkers of inflammation and oxidative stress in adults with cardiometabolic conditions. Four databases were systematically searched for literature in any language (Embase, CINAHL, CENTRAL, and MEDLINE) with 12,177 deduplicated records identified. Seventeen studies of adults with metabolic syndrome, cardiovascular disease, type 2 diabetes, non-alcoholic fatty liver disease or chronic kidney disease were included. Fourteen studies were observational studies, one study was a clinical trial, and one was a randomised controlled trial. Four dietary indices were reported on with most studies (n=11) reporting on the dietary inflammatory index. The most reported biomarker was C-reactive protein. The findings were narratively synthesised. Results were inconclusive due to the heterogeneity of dietary indices and their use, disease states, and biomarkers reported. Only one study reporting on the dietary inflammatory index assessed all 45 parameters. Observational studies, particularly retrospective designs (n=7) are subject to recall and selection biases, potentially presenting overestimated results. Further research is required to determine the relationship between dietary indices and biomarkers of inflammation and oxidative stress in cardiometabolic disease populations. Future research should be rigorous, prospective, assess the full range of index parameters, and examine biomarkers the tool was developed for.