This informative lady's site is more on the unbiased side (as far as diet). http://www.greatdanelady.com/articles/feed_program_for_diabetic_dogs_htm.htm
Great Dane Lady is the hero of a lot of us with giant breeds! Though I don't agree with ANY processed food being good for them, she's more up to date on most things with dog nutrition than anyone else. A person can take all of her nutritional-needs knowledge and make sure they're getting exactly what they need with a raw, human-foods-based diet.
I've been giving Vlad some of the Blackwatch supplements she lists since he was 5 mths old. (
He developed a limp [possible OCD according to vet] and we had to make him stop running. He quit the limp within a week, & the vet has been impressed with my choice of treatment. We'll revisit his type of exercise once he's 18 mths old.)If she says something works, I'd pay attention.