anon101-
It’s really not about the big four to me. It’s about meeting the WSAVA guidelines. Namely, employing a team of experts, including a full-time board-certified veterinary nutritionist and doing feeding trials. The “big four” go over and above the AAFCO requirements in this area.
joannel- You are correct. Toxicity is one of the possibilities the researchers (FDA and several veterinary colleges) are looking into. You may find this interesting: https://avmajournals.avma.org/doi/full/10.2460/javma.253.11.1390
