"Our dogs and cats are eating themselves to death," warns Evan Kirk of the Brewer Animal Hospital in Springfield, Ill. "Their lifespan is short enough already, without making them even shorter by allowing obesity to occur."
To meet the threat, pet-food manufacturers offer diet products almost as diverse as those for humans. One company produces Norwegian kelp for dogs; others promote "holistic dog food" that combines grains, vegetables, fruits and herbal supplements.
The experts recommend more exercise, low-fat diets and fewer snacks. It can be tough medicine for doting pet owners, let alone for their overweight pets.
Julie Churchill operates a weight-loss clinic at the University of Minnesota's College of Veterinary Medicine. "The average American dog these days is a couch potato," she says. "Our mental concept of a healthy puppy is a roly-poly overweight puppy," she says.
Churchill advises owners to reduce the quantity and richness of treats they offer their pets.
Some cat owners seem blase about their pet's waistline, according to a survey released last week by Ralston Purina, the pet food company.
Nearly half the 577 owners didn't know how to determine if their cat was too fat. About 40-percent of those who admitted owning a fat cat also said they were doing nothing about it.
Veterinarians say it's simple to recognize too much weight: Pets will have lost that hourglass figure, and it will be difficult to feel their ribs.
Kirk identifies overweight pets as gluttons who never seem to get enough and "easy keepers" who eat more moderately but have a slow metabolism.
Sedentary people tend to have sedentary pets, Kirk says, and owners who enjoy high-calorie diets tend to pamper their pets with high-calorie treats.
"Pets can have a lot of control over their owners," he says. "When people feed their pet, they see the response, and it makes them feel good.''
Pet owner Erica Fineberg says only one of her cats really needs to lose weight, "He does get his exercise, though,'' she says of Jack, a 20-pound Maine Coon. "My other two cats chase him because he's always after their food.''
Betty, a yellow Labrador, lost 15 pounds following a veterinarian's recommendation. Her owner Bill Deller's set up a regimen that included daily two-mile runs and a switch from canned to dry dog food.
"She wouldn't eat it at first she was looking for more,'' he says. "But it was either that or not eat.''
Like overweight humans, overweight pets are vulnerable to health problems like diabetes, arthritis, and heart disease. Some pets are especially prone to obesity, particularly those that have been neutered and those living in apartments.
"t's humanly impossible for most dog owners to exercise a dog the way they need to be,'' says Randy Klein, co-owner of a pet health-food store in New York City.
She adds that even regular pet food can keep your furry friend trim. "It's not so much what people are feeding their pets as how,'' she says. "A lot of people are leaving food in their bowls all day.''
Experts say pet obesity worsens as food gets tastier and busy owners grow lax. With dogs, exercise can be increased through longer or more frequent walks.
Cats are less likely to embrace such a program, but some enjoy strenuous play, and others can learn to walk on a leash.
"The earlier you start, the easier,'' says Churchill, who takes one of her cats on walks. "Trying to teach an old, obese cat to walk on a leash is pretty tricky.''