Veggies, fruits and nuts may be great for humans, but the same can not be said for dogs. The intestines of a dog is much shorter than that of a human, and has been adapted to process meats (proteins) much more effectively.
And while humans are omnivorous, have dogs since ancient times been primarily carnivorous. Domestication has of course forced dogs to consume a more omnivorous diet, but this is not very healthy to them; and forcing a vegetarian (or vegan) diet onto them, is harmful to their overall digestive system and health.
You will thus want to guard against purchasing dog food, especially for large breed puppies, claiming to be ‘vegan,’ ‘vegetarian,’ or ‘completely natural.’ Ensure your dog food contain a high level of protein, and not as much carbohydrates. (Carbs are actually mostly added to dog food for the binding process, and to add to the volume of the food, more than for nutritional value.)