What out for these pitfalls in commercial diets marketed for cats with allergies, says Dr. Heinze:
Diets “for cats with allergies” that aren’t. “The marketing can be inappropriate,” says Dr. Heinze. “The package may say something like ‘venison and potato’ but when you look at the ingredients, it’s venison and potato plus chicken and duck.” Even if the ingredients are limited, it may contain common allergenic foods such as chicken or fish.
Hypoallergenic diets that aren’t. “This term is often used inappropriately,” says Dr. Heinze. Some novel protein diets — such as rabbit and pea — are marketed as “hypoallergenic,” but “there’s no evidence that rabbit is less likely to cause an allergy than chicken. So if your cat is put on a diet that doesn’t contain that allergenic protein, he or she might do well. But it’s not hypoallergenic.” If your cat has already eaten food with rabbit, for example, he or she might be allergic to rabbit. But hypoallergenic diets with hydrolyzed protein are highly unlikely to cause an allergic reaction in any cat. True hypoallergenic diets containing hydrolyzed protein are only available by a prescription from your veterinarian.
“Novel” or “limited” protein over-the-counter diets that are cross-contaminated. “The best companies work hard to avoid contamination,” says Dr. Heinze. For example, in the pet food industry, manufacturers generally don’t clean their production lines between different formulations. They often just run the second product through the same line and toss the first however many pounds, assuming it’s mixed with the previous diet. But with special diets, particularly hydrolyzed ones, you need to be more careful. “With allergies, it doesn’t take much protein to contaminate a diet and cause symptoms.” Indeed, one study found that some over-the-counter diets labeled as containing only certain ingredients also tested positive for other ingredients that were not on the label.