Food allergies for chewing feet, that seems a little strange. Tully's got a grass allergy so she's always licking her feet, grass allergies are very common in dogs here. I actually found phenergan more effective than benedryl. From all reports, anti-histamines are hit and miss with dogs, so if the benedryl doesn't work you may need to try another brand.
I use Wellness Simple - which has limited ingredients. Has the vet suggested an elimination diet? That's usually the first step with a food allergy. You start with limiting the number of ingredients you give and start with a form of protein they don't usually have and bland vegetables, that's usually a fish and potato diet, for 3 months. I've ended up keeping mine on a fish diet. The get the Wellness Simple fish and potato, and they get fish and vegetables for dinner.
Wow... first thing my vet suggested was allergies without a single, "try this first"... I will check out Wellness simple. Thanks

but I gladly pay