Recent studies have linked ultra-processed foods with neuropsychiatric disorders, and behaviors of relevance to the criminal justice system. This nutritional epidemiology has been bolstered by mechanistic bench science, human intervention trials, addiction science, and advances in microbiome research. Here, we examine this burgeoning research through the lens of diminished capacity and criminal intent. We use recent legal decisions related to auto-brewery syndrome as a way to illustrate how intersecting diet and gut microbiome science is already finding its way to criminal courtrooms. The legalome—microbiome and omics science applied in forensic and legal psychology—is emerging as an important consideration for experts within the field of criminal justice and behavior. It is our contention that decisions related to auto-brewery syndrome are merely a prelude to the ways in which the combination of forensic microbiology and forensic psychology will challenge basic assumptions of free will and mens rea.