Christmas is the time of the year when I struggle most with being a vegetarian. I gave up meat when I was 18, and it was an ethical decision. I loved the taste, and went on holiday to Greece, fairly gorging myself on lamb souvlaki before taking the plunge into a meatless existence. I was a fairly strict vegetarian – I ate eggs and dairy products but nothing that would involve killing an animal to furnish the food on my plate. (Although Hugh Fearnley-Whittingstall once reminded me that the dairy industry involves quite a bit of death, if you’re a male calf, and it’s not all sweetness and light for the female calves and their mothers, either. Thanks for that, Hugh).

Eighteen years later, pregnant with my first child, I started eating fish. Oily fish in particular contains plenty of long-chain omega-3 fatty acids, essential for neural development. Later, I found it too hard to give up, and so I’ve continued eating fish and other seafood, while trying to ensure it’s sustainably sourced. This means I’m now one of those vegetarians I used to frown at – one who occasionally eats fish. And everyone knows that this is a fundamental biological error: fish are not vegetables.

For some time, I pondered whether I could make a meaningful phylogenetic distinction between what I would and wouldn’t eat. Could I draw a line through the tree of life on the planet and decide that one side of it would be fair game, while the other was out of bounds? A natural split seemed to be that between vertebrates and invertebrates. This would mean eating mussels and scallops while eschewing fish. This looked like a logical and meaningful distinction, especially as fish have brains and nerves quite similar to our own, and experiments suggest that they do feel pain. I doubted that mussels and scallops, which possess various clusters of nerves, or ganglia, but lack a true brain, would be aware of pain in the same way (although, intriguingly, scallops do possess up to 100 tiny eyes, which peer out at the world between the two halves of their shells). But what about octopuses? They are invertebrate – and pretty intelligent. The nature of convergent evolution – with similar traits appearing in quite disparate branches of the tree of life – meant that my attempt to base my diet on a phylogenetic distinction didn’t, in the end, make much sense.

I’ve settled for being a lapsed vegetarian. The cognitive dissonance is there, along with a little guilt, but I can live with this level of hypocrisy. After all, I should be accruing some benefits that go beyond the ephemeral enjoyment of eating this delicious stuff. Oily fish is good for heart health, and the NHS recommends eating two portions of fish a week.

On the other hand, there are no health reasons that would persuade me to take up eating red meat again. Quite the opposite. Back in October, 22 scientists met at the WHO International Agency for Research on Cancer, in Lyon, to discuss how unhealthy it might be to eat a lot of red meat and processed meats. They looked at the results of more than 800 studies that had set out to test a possible association between meat-eating and an increased risk of cancer, especially colorectal cancer. The majority of the scientists in Lyon agreed that there was enough evidence to say that processed meats – such as salted, cured, fermented or smoked meats – were indeed carcinogenic. For unprocessed red meat, the evidence was less compelling, but the group still thought it presented a possible risk.

Their deliberations translated into a new WHO classification of red meat as “probably carcinogenic to humans”, while processed meat “is carcinogenic to humans” – in the same category as asbestos and smoking. The new classification hit the headlines, of course. “Bacon, burgers and sausages are as big a cancer threat as cigarettes,” warned one newspaper. But in fact the WHO classification isn’t about how big the threat or the risk is, it’s about whether there’s convincing evidence of carcinogenicity – and for processed meat, there is. But the danger posed by red and processed meat is much less than the risk presented by smoking, and far fewer deaths can be attributed to meat than to tobacco. Globally, around a million people a year die from cancer caused by smoking; about 600,000 die from alcohol-related causes; and about 34,000 deaths are caused by diets high in processed meat.

Still, eating 50g of processed meat every single day increases the risk of colorectal cancer by about 18%. To put that in context, about six people in 100 develop bowel cancer in their lifetime. If they were all to eat a few rashers of bacon, or one sausage, every day, the incidence of bowel cancer would be expected to increase: now seven out of that 100 people would get it.

It’s a sad thought, isn’t it? One or two of those pigs-in-blankets could have cost you a metaphorical hour off your life. And do you know what? I can remember how good they tasted. I’ll just have another glass of buck’s fizz to take my mind off it…