Grains in home cooked food

This one at least has some truth to it. Compared to herbivores a dog's digestive tract is much less specialized for digesting grains, or carbohydrates in general for that matter - especially in their raw, unprocessed form. However, dogs are not true carnivores but opportunistic feeders and can digest and utilize the starch from grains in dog food that has been converted by the cooking process. Digestibility depends on quality and type of grain used: rice (72%) is for example more digestible than wheat (60%) or corn (54%). Dogs can absorb the digestible carbohydrates from rice almost entirely, of the other grains about 20% are not absorbed. Indigestible fiber from grains contribute to intestinal health.