This particular “myth” can be true for some animals - especially cats.  Again we must look at the teeth and digestive tract for clues here.  Humans and herbivores have flat molars that can move back and forth to grind grasses and grains into fine particles.  We produce the enzyme amylase in our saliva which begins to break down carbohydrates - even before they reach the stomach where the job is finished.  Dogs and cats do not produce amylase in their saliva.  Their teeth have sharp edges and do not move from side to side - they cannot “grind” anything in their mouth.

Dogs are considered omnivores of sorts - they can eat and digest grains and vegetables IF they have been somewhat pre-digested as they would be in an herbivore’s stomach or intestines.  Therefore cooked grains are an acceptable source of carbohydrates for most dogs - note that they are an acceptable carbohydrate source, NOT an acceptable source of protein.  Cats on the other hand are obligate carnivores.  They do not digest grains well and become far more easily dehydrated eating dry foods high in carbohydrates.  Cats in the wild tend to derive all their moisture from their prey - they rarely drink water.  Many holistic veterinarians believe the growing prevalence of obesity and diabetes and many other chronic diseases can be at least partially blamed on diets too high in carbohydrates for cats.

Grains should be whole or whole ground grains such as rice, oats, barley, millet, etc. Wheat is a common allergen, so is avoided in the top quality pet foods as is corn.  Wheat and corn are also less digestible for dogs.  Grain by-products such as corn gluten meal, brewers rice, cereal fines and others are less expensive and less nutritious options than whole grains.  Any time a food with grains is fed to a dog or cat digestive enzymes should be added to the food.  This helps improve digestion and enhance utilization of the nutrients in the food.  Digestive enzymes are one of the two most important supplements you can provide for your companion, along with essential fatty acids (fish oil).