but most often your dog or cat will develop sensitivity to one of the main ingredients in the food you're feeding – usually a protein or carbohydrate.
That should be amended to read "usually a PLANT protein..."; as in, SOY
Or maybe, "usually a plant or DENATURED protein..."; as in, some proteins are changed so drastically when cooked, that they can cause the immune system to react adversely to them.
ETA... Generally, a good article, didn't mean to sound snarky.