A randomized controlled trial found that adults with serious mental illness were able to maintain a self-prepared ketogenic diet with high adherence when supported by regular dietitian input. The feasibility signal supports ketogenic metabolic therapy as a realistic intervention design for severe psychiatric populations. The result matters for trial design because adherence and protocol survivability are often major bottlenecks for diet-based approaches in controlled settings. It also sets up future studies to test whether metabolic changes translate into improvements on psychiatric symptom endpoints. The trial’s framing—randomized feasibility with structured dietary support—provides an actionable template for investigators evaluating metabolic interventions in psychiatry.