So what exactly is a grain-free diet made with and why is it so important for dogs? A grain-free diet is a diet made free from wheat, corn, oats, and rice. Options for a grain-free diet exist in wet food, dry food, and treats. Although the typical domestic dog evolved from their ancestors to become more omnivorous, they still require a diet that is high in animal protein and lower in plant-based ingredients such as grains. Novel meat sources such as beef and chicken are great, but rabbit, venison, salmon, trout, and bison are also very high in protein.