A genetic mutation makes Labradors constantly hungry.
Some Labradors are always hungry due to a genetic mutation
Scientists say that the pooches are hard-wired to crave food while burning fewer calories, meaning owners have to beware of the "double whammy" effect to keep their pets slender.
The mutation is present in a quarter of Labradors and two-thirds of flat-coated retrievers.
University of Cambridge expert Dr. Eleanor Raffan explained that dogs, in a similar manner to humans, have genes that influence both interest in food and their metabolic rate.
The scientist told BBC News: "It shows us the power of our genes to change how we feel about food.
"If we get dealt a genetic hand of cards that makes us feel hungry or always want to eat, it takes greater effort to stay slim."
The research develops previous studies into a mutation in a gene known as POMC - which makes dogs hungrier between meals but means they use around 25 per cent less energy while resting.
Dr. Raffan added: "Dogs with this genetic mutation face a double whammy: they not only want to eat more, but also need fewer calories because they're not burning them off as fast."