Gluttonous labradors carry a greedy gene
Interview with
Anyone with a labrador will probably describe their dog using one word: greedy. The breed is notorious for being a bottomless pit; but now science can write them a sick note excusing their gluttony! Because Cambridge researchers have found that a genetic change or mutation in a gene called POMC carried by many members of the breed makes them hungrier; it also makes them burn 25% fewer calories, so they’re more likely to put on weight, even with compensatory exercise. To find out more, I went walkies to meet Cambridge University’s Eleanor Raffan, black labrador Eddie who was hungrily eyeing up my microphone, and his owner, Rowena Edmondson…
Rowena - So we get up in the morning, he gets fed, and then a little bit later we go for a walk. Much of the day he will sleep. If we are eating, he'll come and look hopefully, but he knows there's not much hope.
Chris - A few obvious questions as a co-owner, an owner in common with you, there's never any food left in the bowl. Correct? True or false?
Rowena - True. The other dog's bowl gets licked clean too.
Chris - The bowl would be emptied multiple times if it were refilled?
Rowena - It would, yes. He will never leave any food.
Chris - Hello Eddie. He liked the smell of the microphone, then quite quickly realised he was not going to be able to eat it. What was the background to the study, Eleanor?
Eleanor - We knew this gene was important in how the brain controls appetite and eating behaviour and possibly energy expenditure, but we needed to test whether that was true and whether that really was what was driving the obesity we saw in affected dogs.
Chris - So you put out a call for people with hungry dogs?
Eleanor - Very specifically we didn't actually, what we did was put out a call for people with Labradors and we made no reference at all to whether they were hungry or overweight. In fact, what we did was recruit dogs like Eddie who've been slim throughout their lives.
Chris - How did you test dogs like Eddie?
Eleanor - They all came into our research area in Cambridge and we tested their eating behaviour in a couple of different ways and also their energy expenditure, what their metabolic rate was doing and how many calories they were burning up during their day-to-day lives.
Chris - And then married that up to their DNA profile?
Eleanor - Exactly. And we took slobber samples to get DNA from them all.
Chris - How did you appraise dogs like Eddie's eating behaviors, then?
Eleanor - We tested what we call satiety, the point at which you feel full after a meal, by offering these guys cans of dog food every 20 minutes until they stopped eating. And it turns out that labradors will stop eating in the end, but usually not until around the two kilogram mark, which is an awful lot of food.
Chris - It is an awful lot of food. But that presumably tells you that it's not that they can just accommodate massive great meals that makes them hungry all the time. They will stop. So therefore it has to be a sort of fullness.
Eleanor - Exactly that, and so many people came in and said, 'My dog's never going to stop eating.' But it turns out they do, and that reflects the fact that there are pathways in the body that say, no, that's enough. But the third thing we looked at was hunger. We did that using something we call the sausage in a box test. We showed these guys a sausage and put it in a plastic box that was clear so they could see through it and they could smell it because it had holes in the lid. Then, we videoed what they did, and when we did that we found that dogs like Eddie who had the mutation we were studying were far more attentive to the sausage in the box and paid so much more attention to it and got so much more excited compared to the dogs without the mutation.
Chris - And what about the point you made about burning more energy off? Are they really hungry all the time because they're just getting through huge numbers of calories or are they just greedy?
Eleanor - The other part of our study was to look not just at the amount of energy they might be getting in from their food, but also how much energy they were burning off in maintaining their body's functions. We were astonished by the results which say that dogs like Eddie, who have two copies of the mutation, burn off about a quarter fewer calories every day.
Chris - Tell us about the gene, then: what it does and how it's doing that to dogs like Eddie.
Eleanor - So POMC is a gene that we've long studied as having a role in how the brain controls body weight. It makes sense to have some energy reserves in the body in case there's a period where there's nothing to eat, and so the body has a system to get an appropriate amount of fat mass, and POMC is integral to that system by acting in the brain to dial up and down hunger and energy expenditure. What this mutation is essentially doing is sending the dog's body a starvation signal and the body is responding very sensibly by increasing food intake and also by dialling down how much energy they're burning off to keep the body running. If they really were starving, that would be a very sensible thing to do but, because it's due to a mutation and actually they've got plenty of food, it will tend to make them put on weight if they're given a chance.
Chris - And is that because we've bred them to have a certain set of traits? We've inadvertently bred that in?
Eleanor - Possibly. I'm slightly reluctant to answer this question. In our original study, we had this really intriguing finding that the mutation was more common in guide dogs than it was in pet dogs. That leads to this very tantalising, very tempting hypothesis that maybe we have inadvertently bred our high performing dogs to be a bit foodier because, if you are foodie, you'll do anything for a biscuit and it makes you a bit more trainable. I have tried to test that scientifically and I can't prove it yet. I'm a little bit cautious about talking too much about it, but I think that may still have legs as a hypothesis and may still be true.
Chris - When you tested Eddie, we've heard that he likes his food, what did you find genetically? Where does he sit on this spectrum?
Eleanor - Eddie has two copies of our mutation, so he's at the worse end, he's got a double dose of this. Of course it matters what's in his other genes as well and we have by no means explained why all labradors are greedy. We've just got a bit of it in a quarter of them and we are working very hard on what the other things that are important are too.
Chris - Were you pleased, Rowena, to have an answer to why Eddie is a slave to food?
Rowena - Yes, it's nice to have an explanation, but it didn't really change my behaviour towards him.
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