I'm just gonna copy/paste what I've written before, lol:
One thing is over feeding is a huge problem. People just feed entirely too much. Also, grainfree, higher quality food, you're going to have to feed less of, or you will definitely get runny stools and/or more poop. For example, Jackson, my 15lb'er eats 1/2 cup a day of Acana Grasslands (plus wet food and treats). If he was eating Purina, he would need 1 cup a day or more. Acana is a really calorie dense food. More calories = less you need to feed.
All dogs, including Yorkies, pretty much are wolves. They are taxonomically the same species, and physiologically and anatomically the same and actually share 99.8% of the same DNA. Size and appearance are in the less than .2% differences, therefore I like to feed a food that is 'close' to what the wolves eat in the wild (ok, we know wolves aren't getting served kibble in a bowl... but it's the closest you can get, IMO, besides feeding raw which many do).
High
plant based protein is not good for any dog, healthy or not.
High
animal based protein is good. The better high protein foods derive most of their protein from animal meat.
The early research that convinced people of the myth of high protein damaging dog's liver was done on rats which are omnivores and their digestive system works entirely different than dogs which are carnivores. Rat's bodies are not designed to handle high protein the way dogs are. I am not aware of any research on dogs that points to high protein damaging dog's liver.
Anyways, it's just my personal preference to feed grain free, low carb, meat protein rich foods. Ultimately, though, I think it's what works best for you and your dog.

I've done alot of research and have finally settled that this works best for Jackson!
Btw, I feed both Acana Grasslands and tried out a sample bag of Orijen Regional Red (38% protein) that he liked as well. After this Acana is finished, Orijen will be the next big bag we feed. I also feed Go! Endurance with great results. Those 3 foods are our rotation right now, but he's been eating Acana the longest with great success