He goes through the physical evidence that clearly indicates dogs are well-adapted to eat more than meat, from their ability to synthesize taurine to the relative length of their gut. He also looks at their ability to break down plant starches:
"The next issue is amylase, the enzyme that digests starch. Grains are mostly starch, so an animal would need to make amylase if it is going to digest starch. People have amylase in their saliva, so starch digestion begins when you chew your food. Dogs, like cats, don’t have amylase in their saliva. But this ignores the fact that dogs secrete large amounts of amylase from their pancreas. Since meat doesn’t contain starch, why would dogs need to make amylase in their pancreas? Obviously because they are equipped to eat and digest plant-derived starches. Foxes, which are closely related to dogs, eat just about anything in the wild, from bugs to birds, to fruits, grains and berries. They too are very adaptable 'carnivores'."
His conclusion: "Dogs not only can be healthy on a diet consisting of meat, grains and vegetables, they will do exceptionally well on one."
He must be right, as I completey agree with him (now tell the truth, isn't that how we all think?).
Remember, of course, that regardless of what you feed your dog the most important thing not to over-feed it.