Dear SAS,
I am actually feeding my dear lab Topaz more vegies than meat. Research suggests that protein is associated with skeletal disease. So the lower meat content isn't about weight gain, just joint problems. If you would like, do a search on the internet and there is heaps of info on it. Hence, Topaz is on about 1/3 to 1/2 her meal is meat and the rest is vegies. To get calcium, plain yoghurt and goat's milk are options as are raw meaty bones such as chicken necks, wings or carcasses. The bones help with cleaning their teeth too.
Everything I have added (supplements) to Topaz's meals I have added gradually as the levels she requires are higher due to her hip dysplasia eg OmegaPet is approximately 60-80ml.