Could a vegan diet prevent cancer?

We put this to Giles Yeo, from the MRC Metabolic Diseases Unit in Cambridge...

Kat - So this is a really, really complicated question because, unlike a behaviour like smoking or even drinking alcohol, everyone has a different diet. Everyone eats different amounts of food, all sorts of different types of food, it's different in different parts of the world and, as we heard earlier from Giles, different people have different genetics, and respond differently to the food that they eat. So it's really, really hard to unpick all of this.

Now there are a couple of massive studies that are going on. There's a huge study called EPIC, which is the European Perspective Investigation of Diet and Cancer. I know that Cancer Research UK is helping to fund a big part of that and there's sites in Oxford and Norfolk where they're looking at thousands of people, and in total I think it's half a million people in Europe where they're saying, OK what do you eat, how do you live, how does this affect your risk of cancer and other diseases as well? They're looking at things like diabetes and heart disease.

Now there are a few broad brush things that EPIC has pulled out in terms of diet. So in terms of specific types of foods it has shown that the more red meat, and particularly the more processed meat you have in your diet, the higher your risk of certain types of cancer, and particularly bowel cancer is one of them. If you eat more fish, you have a lower risk of bowel cancer. If you eat more veg, more fibre in your diet, broadly that reduces your risk of certain types of cancer, particularly bowel cancer, and also there's a big part of just your overall body weight. So we know that the more obese you are that does increase your risk of cancer too.

The exact components of the diet and whether being specifically a vegetarian or a vegan is a lot more hard to unpick, particularly because in the studies there aren't that many vegetarians and vegans. So one of the things we do know is that there seems to be a link between a particular growth factor. Something called IGF or insulin-like growth factors and your risk of cancer. That may be linked to animal products, may be linked to dairy. There's a lot of work trying to go on and unpick this but you hear a lot about stuff about - oh there are places in the world where they're completely vegan and they have no cancers at all - that's probably not true

The link between diet and cancer is very complex but broadly, the main things we can say is the more fruit and veg you eat , the more fibre you eat, the less red and processed meat you eat, fish is good, less alcohol is better. Those will broadly help to reduce your risk of cancer as well as keeping physically active and trying to keep a healthy body weight.

Chris - What about smoked fish because I love that?

Kat - Oh yes, so.

Chris - I couldn't not have that.

Kat - So there's a couple of interesting things about. I think smoked fish comes under processed.

Chris - Because, you know, someone did write to me and they said "Chris, I don't understand why smoking is bad for you if it cures salmon."

Kat - Ha has - the cure for salmon! Yes, I mean certainly that comes under processing. We do know that, for example, particularly in Japan where they have a lot of very salty foods and a lot of pickles, that certainly does seem to be associated with an increased risk of stomach cancers. And also, stomach cancer's really interesting because the rates of that, particularly in the West, have gone down massively because a lot of that is linked to 'gone off' food, and the sort of nasty chemicals produced when food goes off. And as everyone has a fridge now, you're much less exposed to those kind of nasties and that's helped to reduce the risk, particularly of stomach cancer.