In one dog breed, selection for utility may have selected for obesity
Selecting trainable dogs may have gotten us dogs that would do anything for a treat.
Labrador retrievers are common pets, but they also work as service dogs, aiding people with sight or hearing impairments. Unfortunately, the breed is particularly prone to getting overweight, and this tendency apparently is more severe in Labradors purpose-bred for service. To figure out the reasons behind this, researchers at Cambridge University investigated potential obesity genes in Labrador retrievers’ DNA.
It turned out increased obesity risk in Labradors was linked to the same genes and mechanisms that cause obesity in humans. These gene variants were more common in purpose-bred dogs we carefully selected, generation after generation, to maximize the results of the demanding training programs service animals must go through.
We thought we were picking the smartest Labradors to become guide dogs. But we might have been picking the ones that just wanted the snacks given as rewards the most.
Nature or nurture?
To figure out which genes were responsible for obesity in Labradors, Cambridge scientists did one of the first genome-wide association studies performed on canines. The technique works by studying small variations in over 30 million bases present in the dogs’ genome and correlating those variations with traits like obesity. “By testing some of those variants along the string of the DNA series we can map areas of the genome which have an association with obesity and within those areas we can spot which genes and what other changes might be responsible,” says Eleanor Raffan, a researcher at Cambridge University and co-author of the study.
Her team checked which genes showed the strongest correlation with increased body condition index, the dog equivalent of BMI, in 241 Labrador Retrievers. They identified the DENN1B as a key obesity gene in these dogs. DENN1B is responsible for, among other things, the regulation and trafficking of melanocortin 4 receptors. “When melanocortin 4 receptors are activated, they tend to turn down hunger,” Raffan explained.
Her team found that lower levels of the DENN1B expression led to more melanocortin 4 receptors, which consequently could turn down hunger for a longer time. Higher levels of DENN1B expression, on the other hand, caused the dogs to get hungry faster and perceive food as more rewarding. But DENN1B was just the most significant of a collection of genes that was correlated with obesity. To handle this complexity, the team created a genetic obesity risk score that took all of these genes into account and calculated values for all 241 Labradors.
The next step was to see how much of an impact genetic risk factors had on Labradors with different daily routines and diets. To estimate that, Raffan’s team used Dog Obesity Risk Assessment questionnaires. “These questionnaires have about 35 items—statements like ‘my dog would eat anything’ or ‘I’m very careful about how I feed my dog,’” says Raffan. Based on the responses of the owners of these Labradors, her team could assess how the dogs were fed, how much exercise they got, and whether they were working service dogs or were just kept at home as pets.
When the team compared the genetic obesity risk scores with the data gathered from the questionnaires, quite a few myths got busted.
Breeding and chocolate
The first conclusion Raffan’s team arrived at was rather predictable. Dogs with high genetic obesity risk were sensitive to how their owners handled their diet and their daily routines. “These high-risk dogs living in a permissive environment where they didn’t get much exercise and where owners were quite relaxed about feeding could gain quite a lot of weight. They could maintain healthy weight when the owners were mindful of their diet and activities,” Raffan says.
High-risk Labradors also tended to pester their owners for food more often. Dogs with low genetic risk scores, on the other hand, stayed slim regardless of whether the owners paid attention to how and whether they were fed or not.
But other findings proved less obvious. “We’ve long known chocolate-colored Labradors are prone to being overweight, and I’ve often heard people say that’s because they’re really popular as pets for young families with toddlers that throw food on the floor all the time and where dogs are just not given that much attention,” Raffan says. Her team’s data showed that chocolate Labradors actually had a much higher genetic obesity risk than yellow or black ones
Some of the Labradors particularly prone to obesity, the study found, were guide dogs, which were included in the initial group. Training a guide dog in the UK usually takes around two years, during which the dogs learn multiple skills, like avoiding obstacles, stopping at curbs, navigating complex environments, and responding to emergency scenarios. Not all dogs are able to successfully finish this training, which is why guide dogs are often selectively bred with other guide dogs in the hope their offspring would have a better chance at making it through the same training.
But it seems that this selective breeding among guide dogs might have had unexpected consequences. “Our results raise the intriguing possibility that we may have inadvertently selected dogs prone to obesity, dogs that really like their food, because that makes them a little bit more trainable. They would do anything for a biscuit,” Raffan says.
The study also found that genes responsible for obesity in dogs are also responsible for obesity in humans. “The impact high genetic risk has on dogs leads to increased appetite. It makes them more interested in food,” Raffan claims. “Exactly the same is true in humans. If you’re at high genetic risk you aren’t inherently lazy or rubbish about overeating—it’s just you are more interested in food and get more reward from it.”
Science, 2025. DOI: 10.1126/science.ads2145
Jacek Krywko is a freelance science and technology writer who covers space exploration, artificial intelligence research, computer science, and all sorts of engineering wizardry.
