A full grown adult dog should be fed around 2-3% of the dog's ideal body weight per day, ideally spread over two meals. If your dog needs to lose some weight, try feeding slightly less than this quantity, or switch to a meat with a lower fat content, until the ideal weight has been achieved. Don't forget that exercise is essential too!
If your dog has been eating the same protein every day for months or years, there is a good chance he or she may develop an allergy to it. Contrary to popular belief, dogs need diversity in their diets just like humans do - so don't be afraid to mix up your usual order a bit and give your dog some variety!