[Patti S]

An adult dog can eat puppy food, if it does extreme physical activities (like sled racing), or it is ill and is trying to put on weight.

If your dog has a normal level of activity, then the puppy food will make him fat over time. Although protein is designed to maintain body tissues and can’t be stored as-is, eating more protein than your (or your dog’s) body requires can lead to extra body fat.