Positive externalities from dog ownership?

Evidence here that dog ownership reduces the risk of obesity and early signs of diabetes among the young…... to which we can add the well known positive effects as an anti-depressant for many of the elderly for whom dogs are incredibly important forms of companionship. On the flip side, I wonder how high is the canine carbon pawprint? A medium-sized dog eats around 360 pounds of meat and over 209 pounds of cereal a year…..