A veterinary nutritionist is a veterinarian who has completed a residency in nutrition and earned diplomate status from the American College of Veterinary Nutrition (ACVN) or its European equivalent (ECVCN). The credential takes 4+ years of post-DVM training plus a written board exam; about 100 ACVN diplomates exist in the US. WSAVA's brand selection criteria require a manufacturer to employ at least one ACVN-certified nutritionist (or PhD in animal nutrition) on staff for formulation. Most pet food brands do not. "Formulated with veterinary input" is marketing language; an ACVN credential is verifiable.