Patients with metabolic acidosis often present with obscure, multifactorial etiologies, making efficient diagnosis and treatment key to preventing poor clinical outcomes. This case report describes a patient with severe metabolic acidosis in which the underlying cause was not immediately apparent. After a thorough work-up and history taking, the patient’s strict ketogenic diet was identified as the most likely source of his illness. Over multiple days, the patient improved as he resumed a normal diet and was treated for refeeding syndrome. This case highlights the importance of taking a comprehensive social and diet history when assessing a patient with metabolic acidosis. It also highlights the need for physicians to understand and be ready to counsel on the possible effects of fad diets, such as the ketogenic diet.