The dietary management of PROP consists of limiting complete (intact, natural) protein containing the propiogenic amino acids; valine (VAL), isoleucine (ILE), methionine (MET) and threonine (THR) to lessen the toxic accumulation of propionic acid. VAL, ILE, MET and THR are indispensable (essential) amino acids, necessary in adequate quantities for protein utilization, anabolism for growth and tissue repair. Early case reports of individuals with PROP treated with restriction of complete protein intake alone, showed poor growth outcomes and clinical signs of inadequate total protein intake. PROP medical foods (formulas) provide protein equivalents restricting propiogenic amino acids while still providing other essential amino acids and nutrients. Cohort studies over the past decades have elucidated ranges of total protein intake with variable proportions of complete protein (including human breastmilk) and PROP medical food protein equivalents. Individuals with more severe forms of PROP require greater restriction of complete protein and rely on additional PROP medical food protein equivalents in order to meet their daily total protein needs. Individuals with milder forms of PROP may tolerate their age-appropriate DRI AI/RDA from complete protein without requiring the addition of PROP medical food protein equivalents.  Should an individual's plasma concentration of ILE and/or VAL fall below the desired range, first consider an increase of complete protein due to a lack of evidence for the efficacy of adding single L-ILE and/or L-VAL amino acid supplements.

Limited data relating energy intake to protein intake and outcomes in PROP have been reported in case studies. In general, energy intake should meet the age-appropriate DRI EER. Energy intake should be adequate under all circumstances to prevent catabolism and the release of propiogenic amino acids from endogenous protein and odd-chain fats from lipid stores. Non-ambulatory individuals and/or those with decreased physical activity due to hypotonia or other neurological complications may need some caloric restriction to prevent obesity. There is no evidence that the recommended intake of fluids, essential fatty acids, vitamins, minerals, and other micronutrients for individuals with PROP differs from that for the general population. Careful and frequent monitoring of dietary intake, adherence to recommendations, and nutritional, clinical and biochemical markers that are essential for adjusting an individual’s PROP medical nutrition therapy is discussed in Question #2.   Additional information about supplementation is discussed in Question #3 and monitoring of nutrition therapy in Question #4.

Definitions of the protein terminology used throughout this guideline are listed in Appendix B.