The Bernese Mountain Dog should do well on a high-quality dog food, whether commercially manufactured or home-prepared with your veterinarian’s supervision and approval. Any diet should be appropriate to the dog’s age (puppy, adult, or senior). Some dogs are prone to getting overweight, so watch your dog’s calorie consumption and weight level. Treats can be an important aid in training, but giving too many can cause obesity. Learn about which human foods are safe for dogs, and which are not. Check with your vet if you have any concerns about your dog’s weight or diet. Clean, fresh water should be available at all times.
From the American Kennel Club