A genetic mutation causes some Labradors and flat-coated retrievers to stay hungry while burning fewer calories, scientists say.
This “double whammy” effect means that dog owners must pay special attention to keeping their pets slim.
The mutation was found in one-in-four Labrador retrievers and two-thirds of flat-coated retrievers.
“This shows us the power of our genes to change how we feel about food,” said the lead scientist.
Dr Eleanor Raffan of the University of Cambridge said dogs, like humans, have genes that influence both food interest and metabolic rate.
“If we get a genetic hand of cards that makes us feel hungry or always want to eat, it takes a lot more effort to stay slim,” he told BBC News.
The study builds on previous research on a mutation in a gene known as POMC.
The POMC gene and the brain pathway it affects are identical in dogs and humans.
Dogs with the mutation not only get hungry between meals but also use about 25% less energy at rest, meaning they don’t need to consume as many calories.
“Dogs with this genetic mutation face a double whammy: not only do they want to eat more, but they also need fewer calories because they don’t burn them as quickly,” Dr Raffan said.
More than 80 pet Labradors took part in the study.
They were given a variety of tests, including the ‘sausage in a box’ test, where they were tempted with a hidden treat that they could see and smell.
Dogs with the POMC mutation tried harder to get the sausage than dogs without it, indicating greater hunger.
The dogs were then allowed to sleep in a special chamber that measured the gases they inhaled showing those with the POMC mutation burned about 25% fewer calories than dogs without it.
Kathryn Taylor has a “big chunky black lab” called Leo, who took part in the study.
He says he will eat anything, including a salad bowl off the table, runner beans from the vegetable beds and has been known to dig up carrots.
“You can feed him and he’ll still want more food,” she said, adding that they’re working to keep him slim with the use of a slow feeder bowl.
As many as two out of three dogs (34-59%) in rich countries are overweight.
Labradors have the highest rates of obesity and have been shown to be more obsessed with food than other breeds.
They make successful working and pet dogs because they are also relatively easy to train.
We may have inadvertently selected for Labradors with the mutation because they love food and will do anything for a biscuit.
The research, published in the journal Science Advances, was funded by the Wellcome Trust and the Dogs Trust.
Follow Helen on Twitter @hbriggs.
