Nano Girl Michelle Dickinson: Clues to obesity not only a dog's dinner

Photo / Greg Bowker

The Labrador retriever is our most popular dog breed, with over 41,000 registered in New Zealand.

I've house-sat for several Labrador owners and more than once made the mistake of leaving the dog alone, only to learn how quickly they can devour everything edible, and not-so edible, in sight.

Labs are renowned for having food-loving personalities and barrel-shaped bodies, but is this an actual behavioural trait within the breed or just a coincidence?

Science may finally have provided an excuse for some owners of extra cuddly Labradors this week, with research suggesting their greedy personality might partially be due to a genetic mutation.

DNA is a molecule containing the unique genetic code to humans and animals. It acts like a recipe book, holding the instructions for how to make the different proteins found in our bodies. The study published in the journal Cell Metabolism looked at the DNA sequences of three specific genes from 18 lean and 15 obese Labradors. These genes were chosen because two of them had already been linked to obesity in humans and mice.

They found that a single genetic variation within one of the three Labrador genes was found to be more common in the obese dogs than in the lean ones. This variation was responsible for disrupting the formation of two chemicals.

Chemical one was b-MSH, which is linked to the ability of an animal to sense the amount of fat it has stored. Chemical two was b-endorphin, which is thought to be involved in the brain's reward pathways.

More than 300 Labradors were then studied and after factors including age, gender and whether they were neutered were taken into account, it was found that dogs with one copy of the mutant gene were 1.9kg heavier than those without, and dogs with two copies of the mutation were around 3.8kg heavier.

This suggests that canine (and possibly human) obesity occurs due to lifestyle factors including lack of exercise and high calorie food intake as well as genetics. Because the gene studied was important in controlling how the brain chemically recognises hunger and the feeling of being full after eating, it could be connected to over-eating and weight gain.

Although we know obesity and over-eating are bad for both our own and our dogs' overall health, we may inadvertently be breeding this gene into our Labradors. Labs are the most common breed used for service, and assistant dogs go through intense training, often using food as reward to reinforce the correct behaviour.

One suggestion is that those dogs most motivated by food might be more likely to work for a treat, thus completing the vigorous selection process and passing on these mutated genes when used to breed other service dogs.

Interestingly of the 81 Labrador assistance dogs studied, 76 per cent of them had at least one copy of the mutant gene implying that service dog exam success and a love of food were related.

However, we can't all blame the extra kilos on genetics as some of the Labs with the mutation were still nice and trim thanks to good diet and plenty of exercise. Also, several other dog breeds were studied and although they did not have the genetic mutation, the groups still contained dogs that were overweight.

So how much of our endemic obesity is a battle against our genes and how much of it can be managed with healthy food and active lifestyles?

This study seems to imply that with diet and exercise, there may be a way to fight your genetics. At least, if your diet is mostly dog food.