Researchers analyzed nearly 1,000 photos of dogs between 2001 and 2013 which placed in the top five at Crufts, the U.K.'s national dog show.
While show dogs are supposed to be ideal specimens, the study authors estimated 25 per cent of the dogs were too chunky. The paper was published online Monday in the BMJ journal, Veterinary Record.
Previous studies have suggested more than half of Britain's pet dogs are too heavy, often just like their human owners.
The breeds most likely to be heavy were pugs, basset hounds and Labrador retrievers, while the skinniest were poodles, Rhodesian ridgebacks and Dobermans.
"Most people see dogs as another member of the family so if the owners are eating too much and not exercising enough, it's not surprising the dog will be overweight too," said Alexander German of the University of Liverpool, one of the study authors.
He said it wasn't clear why certain breeds are predisposed to being rotund, but noted that our perceptions about dogs' appearances have become skewed over time.
"If you're always seeing pugs with some extra padding, it becomes normal," he said. "But there are some slender pugs out there."
German said some of the criteria governing the Crufts show, set by the U.K. Kennel Club, should be revised, noting the standards for basset hounds says those dogs should be of "considerable substance" but gives no guidance on whether that means muscle or fat.
The Kennel Club said it takes dog obesity very seriously and that "judges are trained to only reward healthy dogs."
German said owners should take more responsibility for their dogs' bulging bellies. Though he isn't a dog owner, he did once have a Garfield-like cat named Clarence.
"There's no reason for a pet to be overweight," he said. "It's often just a case of reforming the owners first."