Pets, like people, have dietary needs that change over the course of their lives.

Walking down the pet food aisle of your local store can be a dizzying experience. There is a multitude of choices, and with new products seeming to appear weekly, picking the right food can be extremely confusing for consumers. It’s understandable that pet food companies offer the selection that they do, given that pet owners in the United States spend approximately $20 billion annually feeding their animal companions. There are foods for growing pets, foods for adult pets, foods for senior pets, diet foods, hypoallergenic foods and even foods to improve your pets dental health. Figuring out what to feed and when to feed it can be an overwhelming task.

So how do you decide which food is right?

It depends on the age and condition of your companion. The life of your pet can be broken into three basic phases, each requiring different nutrition for optimal health.

1. The Growth Phase
Growing tissue requires a great deal of energy, so young animals require a diet high in protein and fat that can supply those energy needs. Example: Puppies do best on diets that, in addition to meeting other nutritional requirements, have a specific calcium-phosphorus ratio for appropriate bone growth. Because there are so many different sized dogs, some nutritionists recommend varying puppy foods, with assorted calcium-phosphorous formulations, based on breed. Foods specific to a growing animals needs are important until that animal is close to his adult height.

2. The Adult Phase
Adult animals do best on foods designed to meet their current nutritional needs while helping prevent development of potential health issues such as obesity and tooth decay.

3. The Senior Phase
Pets are considered seniors when they have lived approximately two-thirds of their life expectancy. As your pet ages, changes in his ability to eat and digest food may make choosing a food formulated especially for the mature pet a wise choice.

Regardless of which brand of food you select for your pet, keeping him slender is the best way to help him live a long and healthy life. A 14-year study completed by Purina in 2001 showed that dogs kept at a lean body weight lived almost 2 years longer than heavier dogs. A lean dog has ribs easily felt by light touch and a defined waist clearly visible when viewed from above. In the U.S., obesity is the number one preventable cause of death in companion animals. So when your pet begs for just a little more of that perfect food you’ve chosen, consider a belly rub instead. The health and well-being of your pet may be at stake.

Jennifer Arnold, The New York Times best-selling author of Through a Dogs Eyes and In a Dogs Heart. She is the Founder of Canine Assistants, a nonprofit organization that teaches service dogs to assist children and adults who have physical disabilities, seizure conditions, or other special needs. For more information on Jennifer and Canine Assistants, please visit canineassistants.org or facebook.com/Canine Assistants.