Dogs that are overly heavy or dogs that are too thin are not healthy pets. There is a balance for each individual dog that typically falls somewhere within the average weight range of the breed. There are, of course, exceptions to this rule. Dogs that are mixed breed or dogs that are very large or small compared to the breed standard are doing to have different nutritional requirements. In addition the exercise level that your dog has will greatly impact his or her nutritional requirements.
Most dogs no longer have a job to do which means they are largely around the house most of the day. They may run around the backyard or go for a jog with you every morning, but that is the extent of any type of intensive exercise program they may have. Dog food manufacturers, when calculating the nutritional level of their foods, take this into consideration. On the side panel of the dog food bag, can, pouch or box you will see two different sets of information. One will include the guaranteed analysis and the other will show the ingredients.
The ingredients are listed by weight prior to processing. Many people just look at the first ingredient or two when they make their decision. They may miss several additives, preservatives or other less desirable items listed further down the panel. This is why looking down the list is just as important as what is at the top. The more active a dog is the higher the protein and fat content needs to be. This means that on the ingredient list you are looking for meat items, not meat by products. Fish meal or other types of meat meals is acceptable, but simply listing beef, chicken, salmon, fish or lamb is even better.
The guaranteed analysis lists the protein, fat, water and fiber. This is required by law on dog foods sold in North American and most other countries with some type of quality control. The amount of protein and fat your dog will need depends on their exercise levels and their environment. Dogs that are kept in heated homes in the winter and air conditioned apartments in the summer don't require a lot of energy to maintain their body temperature. On the other hand dogs staying outside in the heat of the summer or the cold of the winter are going to burn more calories just keeping their body temperature constant.
Dogs that have high energy levels and are prone to self exercising during the day will need a larger ration, but often not by much, than dogs that sit on the couch all day waiting for you to get home. Typically dogs that are good at self-exercise are not prone to obesity and weight gain, but the couch dogs are. Lowering the protein and fat content in the sedate dogs diet can help with weight management even if providing additional exercise isn't a viable option.