Story highlights The majority of adult dogs and cats are overweight, study finds

Part of the problem is the "fat pet gap" -- owners unaware pets are overweight, group says

39% of U.S. households own a dog; 33% of households own a cat, Humane Society says

Raleigh, a dog that topped scales at 187 pounds, cut his weight in half

Kim Stevens has a problem that affects tens of millions of Americans. If left untreated, it could lead to the death of someone she loves, someone who's part of the family.

Stevens' dog Dodger, a black and gray mixed breed, is obese. According to a new study, he's emblematic of a growing problem.

The majority of adult dogs and cats in U.S. homes are overweight or obese, and the problem has gotten worse over the past year, according to the Association for Pet Obesity Prevention . Fifty-three percent of adult dogs and 55% of cats were classified as overweight or obese by their veterinarians.

"I didn't notice the weight creeping on -- it was like all of a sudden he was just this fat dog," Stevens said as she and Dodger visited Atlanta's Centennial Olympic Park.

"His weight is about 82 pounds right now, and he should be 62 pounds." That means he needs to lose about a quarter of his weight -- equivalent to a 200-pound person needing to lose 50 pounds.

Photos: Photos: Overweight pets Photos: Photos: Overweight pets Overweight pets – Elizabeth Gutierrez of Pennington, New Jersey, says her 8-year-old cat, Tattoo, is so fat the family has renamed him "Fattoo." The cat should probably weigh 12 pounds, but he's gotten up to more than 22 pounds. The vet has told her Tattoo could develop diabetes and other health problems if he doesn't lose weight. Hide Caption 1 of 9 Photos: Photos: Overweight pets Overweight pets – After Jennifer Smith and her husband brought their basset hound home from the shelter, Buddy would eat to the point he threw up and at his heaviest weighed 92 pounds. It turns out Buddy had a thyroid problem. "Basically, Buddy has no 'stop eating' feeling when he's in front of his bowl," Smith says. They put him on a diet of portion-controlled feedings and trained him not to eat from their other dog's food. Hide Caption 2 of 9 Photos: Photos: Overweight pets Overweight pets – Travis Hux looks at his cat, Baby, with sadness, "knowing his life will probably be cut short." The cat, who should weigh 9 to 12 pounds, now weighs about 20 pounds and has high blood sugar. "I always thought I was doing the right thing because I only fed him cat food and water. I never gave my pets table scraps." He blames an abundance of cheap food and lack of exercise for the cats obesity, adding that it has been hard to force the cat to exercise. Hide Caption 3 of 9 Photos: Photos: Overweight pets Overweight pets – Faye Poirier of Columbia, South Carolina, admits her cat weighs 23 pounds because "I have spoiled her rotten." Poirier liked her fat cat just the way she was, and it was only after the pet became very lethargic and stopped cleaning herself that the owner took her to The Cat Clinic. "Turns out I was feeding her hard food that was full of fillers like paper. They said wet food is the best for them," Poirier says. Poirier followed the vet's instructions her kitty lost weight. Hide Caption 4 of 9 Photos: Photos: Overweight pets Overweight pets – Stacie Schafer says her cat, Sophie, has been overweight most of her life. "The first thing people say when they see her is, 'That is the fattest cat I have ever seen,'" she says. Schafer has tried diet cat food, portion control and exercise to keep her kitty's weight under control, but says Sophie just isn't that interested in running around like her other two cats. "But I do try to get her to go up and down the stairs whenever I can by calling her." Hide Caption 5 of 9 Photos: Photos: Overweight pets Overweight pets – Janie Lambert says she wasn't able to give her foxhound, Jeni, the exercise the dog needed, and within a year of being adopted, Jeni had put on 60 pounds. Lambert's son and daughter-in-law worked with Jeni to get the weight down by cutting her food to 1¾ cup twice a day, a grain-free diet and several walks a day. Hide Caption 6 of 9 Photos: Photos: Overweight pets Overweight pets – Meghan Smith says she knows she and her husband are responsible for their cat Mister's weight problem -- but every time they try to cut back his portions, he "meows a lot and it just seems like he's miserable." He is 8 years old and has ballooned from 12 to 17 pounds since they adopted him in 2006. They use a laser pointer as an exercise tool, "and it does work, but it only lasts a minute." The vet has warned that Mister is at greater risk of developing diabetes. Hide Caption 7 of 9 Photos: Photos: Overweight pets Overweight pets – Beth Spiess of San Marcos, Texas, says her sheltie, Daisy, had become so obese from over-feeding (64 pounds) that she couldn't walk anymore, and her original owners wanted to put the dog to sleep. The vet refused to put her down and surrendered the dog to a shelter in 2010 (Spiess adopted her in July 2011). Since May 2010, Daisy has lost nearly 30 pounds through a rigid diet -- 1/4 cup grain-free kibble, 1/4 cup frozen green beans twice a day and poached, boneless, skinless chicken bits as treats -- regular walks and no people food. Hide Caption 8 of 9 Photos: Photos: Overweight pets Overweight pets – Karrie Kelly of Ottawa, Canada, first noticed there was something wrong with her cat, Maverick, when he stopped jumping on the furniture. Maverick was diagnosed with arthritis and put on a reduced-calorie diet. But Kelly says Maverick lost weight too quickly and developed Feline Hepatic Lipidosis. She says Maverick was close to dying but had a "remarkable recovery" after treatment. She now tells everyone about "the dangers of unmonitored weight loss." (Maverick died in April due to another condition at age 13.) Hide Caption 9 of 9

The reason is pretty simple: "Too much food and not enough exercise," Stevens said.

The Association for Pet Obesity Prevention report shows not only that more pets are overweight, but also that those with the problem "are getting fatter," said Ernie Ward, the group's founder.

The annual study, to be released next week and given in advance to CNN, found that 25% of cats and just more than 21% of dogs are obese. Both those figures are up slightly from 2010.

About 41 million dogs and 47 million cats are overweight or obese, the study found.

About 41 million dogs are overweight.

A long list of health dangers comes with the excess weight. "It's not a matter of if, it's when" serious complications will strike, said Ward.

These can include high blood pressure, "crippling arthritis," diabetes and some cancers. "Their life is shortened by two or 2½ years," said Ward, a veterinarian in North Carolina.

The U.S. Food and Drug Administration's Center for Veterinary Medicine, which cites the association's annual study, said the diseases seen among obese pets "are eerily similar to those reported for people."

A central part of the problem, the pet obesity group found, is the growing "fat pet gap:" More and more owners are unaware their pets are overweight. The study found that 22% of dog owners and 15% of cat owners characterized their pets as normal weight when the animals were actually overweight or obese.

"In simplest terms, we've made fat pets the new normal," said Ward.

In many cases, the problem correlates to the obesity epidemic among people, he said.

"This is the sentinel for childhood obesity. When I see dogs who are overweight, I see a child that's at risk for excess weight, because nobody's exercising. The kid's playing video games all day, the dog sits around all day," and "everybody's eating poorly."

Stevens said she needs to shed some weight, too.

"We'll do it together," she said.

The fact that obesity has struck her dog is particularly telling. Stevens does some work as a dog trainer. "To have a dog this heavy when you know better ... is embarrassing," she said.

Thirty-nine percent of U.S. households own at least one dog, and 33% of households own at least one cat, according to the But she has a lot of company.Thirty-nine percent of U.S. households own at least one dog, and 33% of households own at least one cat, according to the Humane Society of the United States

About a third of U.S. households own a cat.

The pet obesity survey was conducted at 41 veterinary clinics across the country and included evaluations of a sampling of more than 600 animals. "Over the five years studied, these results have proven to be consistent and increasing at a gradual pace," the association said.

While the obvious advice -- eat less, exercise more -- is the right starting point, there's more that pet owners should understand, Ward said.

Pet foods these days are "more calorically dense" than they used to be, yet owners are feeding their pets more, he said.

If you're concerned your pet may be obese, it's important to work with a veterinarian, and not try to tackle the problem on your own, said Ward. "Diet is not about starvation or deprivation. It's about gradual weight loss."

In many cases, carefully measuring food and committing to exercise can do the trick. But more severe cases need more extensive work.

That's what helped Jane Whitehead's dog, Raleigh.

In February 2006, he weighed a whopping 187 pounds.

"I swear, we didn't overfeed him!" Whitehead said of Raleigh who, like Dodger, is a rescue dog.

"We would try giving him smaller and smaller portions of his regular food and he kept gaining and kept gaining."

A series of tests found nothing wrong with him, but "at a certain point when he had become so obese, he couldn't exercise at all. We would try to walk him a little bit and he would just stop," said Whitehead, CFO of a business in Duluth, Georgia.

A veterinarian switched him to "super low-calorie food" and put Raleigh on an underwater treadmill, which he loved.

"He lost enough that he could exercise on his own and go for walks with us." The energetic Raleigh she loved was back.

Within three years, Raleigh had cut his weight in half.

There are few truly lost causes, Ward said. And that's something critical for owners to know.

Beth Spiess of San Marcos, Texas, said her sheltie, Daisy, became so obese from over-feeding that she couldn't walk, and her previous owners wanted to put her to sleep. The vet refused and gave the dog to a shelter, where Spiess adopted her. Daisy has lost 30 pounds.

Daisy has lost nearly 30 pounds through a rigid diet.

"It's hard to believe she is the same dog," Spiess told CNN in an iReport, though Daisy still needs pills to help with arthritis caused by the obesity.

Cat owners can face more of an uphill climb in trying to get their pets to exercise, Ward said.

Stacie Schafer of Brunswick, Ohio, said people often remark that her cat, Sophie -- now nicknamed Meatloaf -- "is the fattest cat I have ever seen." Schafer has tried to get Sophie to run around like the other two cats in the home, but Sophie just isn't that interested.

"Cats don't jog," Ward said. "Cats by nature are anaerobic creatures. That means they use sugar as their primary energy source. ... They sprint, they pounce, they leap."

Schafer has tried diet cat food and portion control as well, with little results.

Ward recommends families facing trouble work with veterinarians to find ways to bring down the weight.

In the end, living a life in which you prioritize healthy eating and exercise for all members of the family, including domesticated furry friends, is the key, he said. That means no more treats -- "calorie grenades" -- every time your dog does a trick. "They want reward, praise, affection. We take the easy way out, reach into the cookie jar."

It also means snacking on single-ingredient treats like celery, broccoli and asparagus.

And it means moving to stay healthy and stay alive.

"Unless we really get a grip on this very quickly," said Ward, "We're going to see an entire generation of pets that don't live as long as the pets I had when I was a child."