Jeanette Potter

Jeanette Potter, left, a veterinary technician, and Eric Pihl hold Bonnie, Pihl's shepherd mix, during a free swim before beginning her exercise on the underwater treadmill at TheraPET in Buffalo Grove. (Andrew A. Nelles/For the Chicago Tribune)

"We didn't get as good of compliance as we hoped for, but I think we will try it again this fall," Bishop said. "It's all about diet and exercise."

He cautions pet owners to go slow in exercising an overweight pet, and to talk to their vet about their animal's nutritional needs.

Charlene Numrych, of Chicago, takes her 9-year-old Labrador retriever mix, Cooper, twice a week to the Buffalo Grove clinic to walk and swim. She also has changed his diet and is pleased with the results.

Although plagued by numerous health problems, including hip dysplasia and cancer that required partial amputation of his right front leg, Cooper has dropped from 130 pounds to 107.

"You can see the bounce in his step again," Numrych said.

She has also replaced treats with attention, giving Cooper more massages and play time.

In 2006, Hill's Pet Nutrition Inc. approached Dr. Robert Kushnar, medical director for the Center for Lifestyle Medicine at Northwestern Memorial Hospital. The Topeka, Kan.-based pet food company was interested in having him conduct a study looking for a correlation between the parallel epidemics of human and pet obesity.

Kushnar's study found that people lost weight whether they owned a dog or not, but those who buddied up with their dogs got enjoyment from exercising and were more apt to continue.

The dogs, he said, often acted as a prompt or incentive and would be standing at the door, waiting patiently, nudging their owners to take them out, he said.

"We know that if exercising isn't fun, you aren't going to stay with it, and that part of losing weight is exercise," he said. "A dog is the best exercise machine on a leash that you can find."

Having Bonnie around has forced Pihl to take a walk after work, even on the days when he doesn't feel like it.

"We both benefit," he said. "There are great social benefits to having a dog. I work with people who say they don't know their neighbors. I can say I know my neighbors, and they know me and Bonnie."