Can diet foods keep your four-legged friend fit?
Credit: Photography Thayer Allyson Gowdy / Dog: Brooklyn/ Bow-Wow

As you contemplate your health and diet, you might consider your pets, too. About 25 percent of cats and dogs in the United States are overweight, according to research studies -- and the possible health risks include diabetes and heart disease.

Fortunately, just as there are healthy low-fat items for humans, there are light alternatives for the four-footed. In order to qualify as a "light" pet food under industry regulations, a formula must contain around 20 percent fewer calories than the average commercial dry food. Most companies reduce calories in their products by decreasing fat, or adding fiber or (in the case of canned foods) water, according to William S. Swecker Jr., D.V.M., past president of the American College of Veterinary Nutrition.

But not all diet pet foods are created equal. One brand's light food may have the same number of calories as another line's regular food, says Craig D. Thatcher, D.V.M., Ph.D, professor and clinical nutritionist at the Virginia-Maryland Regional College of Veterinary Medicine. "So it's not as easy as just saying, 'If it's labeled diet, it's diet.' You need to compare its caloric density to the food that you're currently feeding your pet."

Swecker is unable to declare any one brand a winner but doesn't hesitate to reaffirm the universal weight-loss truth: "Weight reduction in pets, just like in humans, is best achieved with a change in diet and behavior." That means more walks for Fido, more catnip-mouse chasing for Fluffy, and less overfeeding for both.

Put Your Pet to the Test
To determine whether your pet needs to drop a few pounds, start by comparing its weight measurements from annual vet visits. Doctors Thatcher and Swecker also recommend the use of "body-condition scoring," which involves a visual and hands-on appraisal of how over- or underweight your pet is. Body-condition charts are available through pet food companies or -- better yet -- your veterinarian, who can also provide food recommendations and a weight reduction plan, as well as monitor your pet's progress between visits.