Utilizing organic waste as a resource is made sustainable and efficient via anaerobic digestion. Direct Interspecies Electron Transfer (DIET), which facilitates the syntrophic conversion of different organics to methane, has recently gained attention through the use of conductive materials during anaerobic digestion. The most recent research on DIET processes with various mediating pathways is thoroughly summarised in this study. The impact of diet on the efficiency of anaerobic digestion as well as the underlying mechanisms affecting the lag phase, methane generation, and system stability are all being extensively investigated. Current issues are also thoroughly examined, including ambiguous biological mechanisms, the effects of non-diet mechanisms, the limitations of organic materials syntrophically oxidised by means of diet, and issues with the practical application of diet mediated by conductive materials. Finally, prospective research directions for the use of diet in practice are presented.
