Introduction: Propionic and methylmalonic acidemia (PA/MMA) are rare inborn errors of metabolism characterized by accumulation of propionyl CoA and/or methylmalonyl CoA, resulting in potentially serious metabolic crises arid clinical complications. The gut microbiota contributes a significant proportion of total propionate production and provides a potentially modifiable target. Empiric use of oral antibiotics to reduce propionate production is a common approach but is hampered by possible drug resistance, perturbation of normal gut microbiota, and toxicity. Moreover, constipation, associated with low fiber intake, inadequate fluid intake, low gut motility, and other factors, is a chronic problem in this patient population and may influence propionate production. Newer management techniques that reduce the burden of propionate and address these clinical challenges are needed.