Why can't dogs eat chocolate?

Chris Smith asked vet Stuart Eves from Cambrudge University to break down this question from Caoibhe on Twitter. Then panellists Jacob Dunn and Eleanor Drinkwater had a question of their own.

Stuart - Well it's quite timely given that Easter is coming and, certainly for vets, that's the big time when these things tend to happen. The fact is that chocolate contains an active ingredient, theobromine, which is relatively toxic and it has a certain kind of toxic element to us but we metabolise it. We break it down into various compounds rapidly. And while we have some activity it’s much less so. On the other hand, unfortunately, dogs have this enzyme pathway, this way of breaking it down which creates a lot of very active components.

And what that usually means is - I think the numbers go something along these lines - if we would break it down, it should be half gone after in about six hours, whereas for dogs, it is something like eighteen. It just stays too high too long for them. Now the one thing to say is it does depend on the chocolate and, every vet out there will know, we will have these anecdotes of a Jack Russell which ate a large bar of chocolate and seemed fine and then we have one of a great dane which ate a small amount of chocolate and there was a problem. So the dose varies massively and the quality of the chocolate really matters.

Chris - What does it do to the dog? How would you know if your dog had got chocolate poisoned? Obviously, you'll see the wrapper left on the floor.... But how might you spot this?

Stuart - Absolutely. It's a stimulant so it's actually very similar to caffeine in coffee or something called theophylline which is in tea. So heart rate goes up, blood pressure changes all over the place. The usual response, and we've already been on vomiting so I feel okay to now broach this, the usual response of dogs is to vomit and actually hopefully that's the best thing if they have brought it up. But they're the kind of signs you see.

Chris - Jacob?

Jacob - I was just gonna ask whether dogs are lactose tolerant because quite a lot of cats are lactose intolerant, aren't they? Presumably it's milk chocolate, that might be another cause of tummy is getting a bit funny.

Stuart - Yes, tummy is going funny? Yes, in theory, absolutely. That's kind of okay. I'm more worried about you get these nice chocolates now that contain raisins. Now there's a problem with raisins and dogs and coffee beans.

Chris - Really?

Stuart - Yeah, that was the tannins in raisins are another risk factor. Raisins themselves are quite toxic.

Chris - I had a dog that loved grapes and, of course, a raisin is just a dried grape.

Stuart - Yes, so they’re concentrate if you dry them so it's the difference between grapes and wine I guess so it's just the combination that you have.

Eleanor - What about other types of pets, what about cats? Can cats eat chocolate or is it the same story?

Stuart - It would be the same story but they don't. And the underlying reason is actually that cats have a defect in one of their two taste receptors. When they actually taste sugar and when we taste sugar it's made up of two halves of a receptor. Cats actually have a defect in one of them which means they don't taste sweet stuff so they won't eat it. I hope I'm right on that one but that's certainly what was said.

Chris - So you’re saying, if you gave them a choice between something sweet and something not sweet they would not be able to discriminate?

Stuart - No, because they can't taste sweet. They live on protein bars of mice then it doesn't matter. You don't need to, so no.