From the tiniest teacup poodle to the most massive Great Dane, dogs' digestive systems are pure wolf. Fido's ancestors enjoyed a diet that was 45 to 50 percent protein, 40 to 50 percent fat, and less than 10 percent carbohydrates. Walk down the pet food aisle, however, and you'll find that typical commercial kibble is made mainly of starchy ingredients like peas, potatoes, corn, wheat, rice, and oats--nothing a prehistoric pup would dream of eating. This "healthy" mix is proving anything but: About 85 percent of dogs eat commercial dog food, and at least half of them are overweight or...