You may not be able to teach an old dog new tricks, but you'll have to get it used to a new diet. Older dogs tend to become overweight. This is a natural result of a slowed metabolism that comes with age. It only contributes to the problem when pet owners fail to take account for this and don't adjust their dog's diet accordingly. It's understandable that some owners hate to think about the fact that their dog is getting on in years, but it's best for the animal to adjust its dietary needs.
Because of this slowed metabolism and reduced activity and exercise, older dogs require fewer calories. Specifically, they need about 20 percent fewer calories than the average adult dog [source: National Academies]. And, to aid their digestive system, they benefit from a diet with additional fiber. You may notice several senior dog foods that boast low amounts of protein. However, unless your vet recommends a low-protein diet for a condition like liver or kidney failure, don't assume that your dog will benefit from it. In fact, many experts say older dogs need even more protein than younger adult dogs to keep up their protein reserves. The need for high-quality protein is probably even more important at this stage of life, since it's more easily digestible.
Due to sensory loss that comes with old age, senior dogs may not have as big of an appetite as they used to. If this gets so bad that they're no longer maintaining a balanced diet, you can try tempting them with different foods or heating up their meals [source: Becker]. And because maintaining water balance gets more difficult for their aging bodies, always have water available to them [source: Kam].