Grain free diets are a newer trend in the pet food industry, but they may not be the right choice for most pets.  It is known that starches are less digestible and have more limiting protein availability than animal-based protein sources in general terms in addition to the belief that starches (grains in particular) are "filler" and sources of food allergies.  While some starches do show up on lists of potential food allergens in dogs and cats (corn, wheat, rice, for example), they are not common causes of food allergy as the protein source is the more likely culprit and a true food allergy is quite uncommon in dogs and cats.  I will note that there is a difference between a food intolerance and a food allergy as an allergy is a true immune response, which most dogs and cats do not actually have.  The other notion is that starches are "fillers" implying they have no nutritional value, which is also not true.

Some pets may need a grain free diet, but those would be animals that are truly allergic to the grain in the food or those that have a grain intolerance, gluten enteropathy has been found in some Irish Setters. A dog that does not have allergy or intolerance does not need to be on a grain free diet.

Recent studies have suggested that grain free diets could be dangerous. There has been an association of grain free diets with dilated cardiomyopathy in dogs.  Yet, the exact cause is poorly understood.  There is one publication documenting taurine deficiency associated dilated cardiomyopathy in golden retrievers eating grain free diets.  However, the study involved a small number of dogs and a limited number of grain free diets identified in that study relative to the number of grain free diets that are commercially available.  There is another study that showed echocardiographic changes (heart ultrasound) in dogs fed grain free diets; however, it was not linked to taurine or carnitine deficiency.

Veterinary nutritionists are left wondering why we are only now seeing these problems when grain free diets have been around for many years?   And if it is not a specific nutrient in terms of amount of the nutrient, such as taurine or carnintine, then what is it?  And perhaps it isn't the nutrients, per se, but the fact that these are processed foods and perhaps there is an issue with the processing and therefore production of conventional pet foods.  We do agree that further studies are needed to really understand the association.