A dog's nutritional health depends on receiving the correct amounts and proportions of nutrients from the six required groups:

• Water: All animals depend on water for life processes. Water is found inside and outside cells, and is involved in most biochemical reactions within the body.
• Protein: Made up of amino acids, protein serves numerous functions in the body including muscle development and tissue repair. Protein also supports immune function, the synthesis of enzymes and hormone production, and can be utilized for energy.
• Fat: A concentrated form of energy, and can also be a source of essential fatty acids required by dogs for maintaining healthy skin and haircoat. Fat also serves as a carrier for fat soluble vitamins.
• Carbohydrate: Consists of sugars, starches and dietary fiber. Some can be readily burned as energy, while whole fiber provides health benefits in the gastrointestinal tract.
• Minerals: Inorganic elements that support many functions, including bone and cartilage formation, enzymatic reactions, maintaining fluid balance, transportation of oxygen in the blood, normal muscle and nerve function, and the production of hormones.
• Vitamins: Vitamins work in concert with other vitamins and nutrients to nourish the animal in various ways. Different vitamins play roles in maintaining the health of different systems in your dog's body.

With the exception of water, commercial dog foods identified as 100% complete and balanced contain all of these required nutrients per the stated life stage. These nutrients are also present in the proper proportions. Remember that nutritional requirements change with age and reproductive status.  Some foods may not be appropriate for all life stages so one should check the label for information regarding this.

The other crucial measure of a dog food is energy, measured in calories. Energy in the form of calories provides the driving force in metabolic reactions and supports the utilization of all other nutrients.

Depending on your dog’s age, breed size, environment and activity level, energy needs will vary. While you need to make sure you’re giving your dog enough calories, you also don’t want to give too many, or your dog’s body will store the extra energy as fat, which can lead to obesity.