Colorado is said to have the fittest residents in the U.S., but it has a secret underbelly. And it is fat and furry.

Denver ranks among the top five cities for most overweight pets, along with Minneapolis, Salt Lake City, Seattle and Boston, according to the State of Pet Health 2012 Report.

In Denver — which comes in fourth-fattest — 24 percent of dogs and 26 percent of cats were overweight or obese in 2011.

Just under 20 percent of Colorado humans were reportedly overweight last year, according to the federal Centers for Disease Control and Prevention.

Yet Colorado ties for seventh among states with the highest proportion of clinically fat dogs. Colorado’s fat cats also place among the top seven heaviest.

The report, compiled by Banfield Applied Research and Knowledge, or BARK, captured and analyzed medical data from the chain of Banfield Pet Hospital’s almost 2 million client dogs and 430,000 client cats.

The report shows that, nationwide, over the past five years, overweight and obesity have increased by 37 percent in dogs and 90 percent in cats.

Now almost 1 in 5 pets are too heavy nationally (1 in 4 in Denver and Colorado), compared with 1 in 3 human Americans, BARK reports.

Dogs match people poundage only in Minnesota, where Banfield reports 38 percent of dogs are overweight. And 41 percent of Minnesota cats weigh in too heavy. Me-ouch!

Rhonda Siegel said she’s watched family pooches get pudgier every year since 2005, when she opened the Canine Fitness and Fun Center in Denver.

“We do love them to death,” Siegel said. “A lot of dogs are really food-motivated. We use that too much.”

Banfield veterinarian Heather Howells said the pet obesity epidemic affects all breeds and all ages of dogs and cats, though mature animals and large-breed dogs are more at risk.

Overweight and obesity are primary concerns, Howells said, because of their association with serious chronic diseases, including arthritis, kidney disease, thyroid disease and heart disease.

“You can’t love your pet too much, but you can feed them too much,” Howells said.

And the trouble is often in the treat jar. Rawhide might look like cardboard, but it’s high in calories. Bully sticks have many more calories than sticks found in nature. Other treats are high in sugar.

“There are treats for your pets that aren’t food,” Siegel said. “Attention. Just attention works.”

It’s not as if dogs don’t like exercise. Most of them love it.

“Oh, no. Now I have something else to feel guilty about,” said Brenda Carlson, when asked whether she knew Denver pets were some of the pudgiest in the country.

Her nearly 9-year-old yellow Lab, Herc,

has been packing on the pounds the past couple of years, she said. She has no idea how much he weighs, but he can no longer jump into her SUV on his own, and she can barely help lift him. It embarrasses them both, she said.

But Friday, they enjoyed a great game of fetching tennis balls at a dog park.

“Every time we come (to the park), we have a really good time. I don’t know why we don’t come more. I’m just really busy,” she said. “I feel terrible.”

Pet obesity also is a problem of perception.

“Most of our clients believe their pets are just the right weight,” Howells said. “They’re surprised to hear they’re overweight.”

She talks to more clients concerned that their animals are too thin, when their pets are merely slender.

You can’t tell by looking at your pet, she said. Dogs and cats usually look just right to their owners. A pet is at an ideal weight if ribs are easily felt but not seen. There should be an obvious waist.

If overweight — 20 percent above ideal weight — a pet’s ribs eventually can be found and felt, and a waist is barely visible. If obese — 40 percent over ideal weight — a pet’s ribs and waist apparently are absent.

A pet can be too thin — ribs are easily visible and waist severely defined.

If you think your pets aren’t aware of how they look, Siegel offers this observation based on seven years of dog-day-care experience.

“When dogs get really bad haircuts, they just don’t act like themselves. They appear self-conscious,” she said. “We really praise them to try to get them over it.”

And when dogs can’t keep up with other dogs, she said, it bothers them.

Electa Draper: 303-954-1276 or edraper@denverpost.com