When your dog looks up at you hopefully with big, sad eyes, begging for a treat, it can be hard to say no — in spite of your best intentions for restricting your pet to a healthier diet.

And one dog breed tests their owners more frequently, with more persistent begging than other breeds, according to a new study.

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Labrador retrievers were found to be more inclined than other dog breeds to beg for treats, and to generally engage in behaviors related to getting more food. And the reason lies in their DNA, researchers found.

The study's lead author, Eleanor Raffan — a veterinary surgeon and geneticist at the University of Cambridge in England — told Live Science that she was inspired to explore labrador obesity because she was seeing an unusually high number of overweight labs in her veterinary clinic.

"When I speak to their owners, everybody says, 'My dog is really obsessed with food,'" Raffan said. "And whenever we see something that is more common in one breed of dog than another, genetics are implicated as a possible factor."

So Raffan set out to learn more about labrador biology and to see if there was a genetic explanation.

DNA evidence

For the study, Raffan and her colleagues first looked at 33 labradors — 18 that were fit and 15 that were obese — focusing on genes known to be associated with obesity. They found that the obese dogs were more likely to carry a variation of a gene called POMC that was "scrambled" in one spot, according to Raffan.

Labrador owners should be aware that their dogs are hard-wired to pester them more about food

The gene variant essentially omitted an "off" switch from hunger cues. "So, that 'off' switch doesn't work properly anymore, and the dogs are much more motivated by food," she said.

After studying more than 700 additional labs, they found the POMC gene variation in about 23 percent of the dogs — approximately 1 in 4 labradors is likely to carry this variant, the scientists noted. Not all of the labradors with the "scrambled" gene were obese, but Raffan and her colleagues found that those dogs with the gene were more likely to beg and scavenge for food, according to surveys provided by their owners.

An evaluation of 38 other dog breeds revealed this gene variation in only one other breed — flat coat retrievers, which are closely related to labradors.

"This is a common genetic variant in labradors and has a significant effect on those dogs that carry it, so it is likely that this helps explain why labradors are more prone to being overweight in comparison to other breeds," Raffan said in a statement.

"No magic wand"

Unfortunately, there is no "quick fix" for overweight labradors, Raffan said. If your dog is overweight — no matter what the breed — regulating food and increasing exercise are your best bets for a healthier pet.

But labrador owners should be aware that their dogs are hard-wired to pester them more about food, and are more likely to beg, Raffan added. That doesn't mean labrador owners should just give up on trying to control their dogs' food intake — but there will be somewhat more effort involved, in order to resist the more frequent begging.

"If they're overweight, it's not that you can't fight the biology — but it's more difficult," Raffan said. "Just recognize that it's much harder work for you than for someone who has a dog that isn't bothered about food."

The findings were published online May 3 in the journal Cell Metabolism.