ELISA testing for soy antigens in dry dog foods used in dietary elimination trials

The use of elimination diet trials is necessary in the diagnosis of food allergies and intolerances. The objective of this study was to determine in vitro if four over-the-counter (OTC) dry dog foods carrying a "no soy" claim and seven veterinary therapeutic dry dog foods designed for food elimination trials were suitable for a soybean elimination trial. A 100 g sample of each diet plus one soy positive and one soy negative control diet were submitted for enzyme-linked immunosorbent assay testing to an independent food laboratory. The positive control diet contained >25 ppm soy protein antigens and the negative control contained <2.5 ppm. Three of the four OTC "no soy" claiming diets were positive for soy antigen. Two of the three soy-containing diets had >25 ppm. Three veterinary therapeutic diets had less than the lowest detectable limit of soy protein and four were positive (>2.5 ppm). OTC dog food diets that claim to contain "no soy" may contain high concentrations of soy protein and, therefore, should not be used in soy elimination trials in suspect food allergic dogs. The veterinary therapeutic diet selected for a soy elimination trial needs to be carefully chosen based on diet history.