Many factors to consider. If your dog is perfectly healthy, there is no reason to switch to less calories, less protein, less anything. More vitamins and supplements actually. So this would be the time to do a full medical checkup. From oral, to kidneys to liver to thyroid, etc. Those are the issues for tweaking a canine’s diet. It’s like if you turned 65 and everyone took all your foods away, and slapped down some oatmeal.