According to data from the American Kennel Club, the Labrador Retriever is the most popular dog in the United States — for the 31st time in a row. Americans love their labs, just like labs love their chow. As dog owners can attest, labradors make for very loving, caring, and loyal pets. They’re also inclined to gain a lot of weight, which puts them at a great health risk. It’s not their fault though.

New research by veterinarians and geneticists at the University of Cambridge uncovered a genetic mutation that may explain this breed’s seemingly endless hunger and tendency toward obesity.

They’re not fat. It’s just genetic

The researchers led by Dr. Eleanor Raffan zoomed in on the pro-opiomelanocortin (POMC) gene, which plays a crucial role in regulating hunger and how they burn calories. Labradors, along with flat-coated retrievers, are more likely to carry a mutation in this gene.

Raffan and colleagues ran experiments with 80 Labradors, which underwent various tests. Among them was the ‘sausage box’ test, which tempted the voracious dogs with a treat they could smell and see through the transparent walls of a box. The labs with the POMC mutation were much more adamant about reaching the hidden treat than dogs without the mutation. All canines were fed a standard breakfast before the sausage-in-a-box task.

In another experiment, flat-coated retrievers slept in a special enclosure where a device measured the gases they breathed out. The flat-coats with the POMC mutation burned 25% fewer calories than dogs without it.

About one in four Labrador Retrievers and two-thirds of flat-coated retrievers have the mutation. Previous studies found that the Labrador has the highest obesity rate among all dogs.

Problems with POMC also affect humans. Babies with compromised POMC function are constantly hungry, and become obese at a very early age.

This genetic quirk results in a “double whammy” for affected dogs. They not only feel an increased urge to eat but also have a reduced rate of metabolism, meaning they burn fewer calories from the food they eat. Interestingly, the researchers found this mutation is a legacy from the St. John’s water dogs, an extinct breed that thrived on a high-calorie diet to survive the cold maritime conditions of Canada centuries ago. So what was once an evolutionary advantage is now a huge bane for labs — not that they don’t enjoy the food, of course.

Difficult but doable

“All owners of Labradors and flat-coated retrievers need to watch what they’re feeding these highly food-motivated dogs, to keep them a healthy weight,” Raffan said.

Despite these genetic predispositions, obesity in Labradors is not inevitable. Owners can manage their pets’ weight through diet, exercise, and mental stimulation. Strategies such as dividing meals throughout the day and ensuring ample physical activity can help keep these dogs at a healthy weight. That’s if you can resist their pleading puppy eyes.

“People are often rude about the owners of fat dogs, blaming them for not properly managing their dogs’ diet and exercise. But we’ve shown that Labradors with this genetic mutation are looking for food all the time, trying to increase their energy intake. It’s very difficult to keep these dogs slim, but it can be done,” Raffan said.

The findings appeared in the journal Science Advances.