Transcript:

Buddhini: Hi everyone and thanks for joining this next Cancer Research UK and Science on Google+ hangout on air. Today we’re talking about the links between processed meat and cancer which came about in the wake of the recent announcement from the IARC – that’s the International Agency for Research on Cancer (part of the World Health Organisation). They announced that processed meat has been classified as a definite cause of cancer and red meat is a probable cause of cancer, which led to the headlines we saw saying bacon will kill you, burgers will kill you. But what exactly is the risk, and should we be giving up bacon and burgers? Is it really as bad as smoking? To find out we’re joined by Dr Kathryn Bradbury and Professor Owen Sansom. If you two can please introduce yourselves and say what you work on then we can dive straight into the questions.

Kathryn: I’m Dr Kathryn Bradbury from the Nuffield Department of Population Health at the University of Oxford and I look at dietary risk factors of disease and large population studies.

Owen: I’m Professor Owen Sansom from the CR UK Beatson Institute in Glasgow and my lab works on trying to understand the early changes of epithelial cancers, particularly bowel cancers.

Kat: I’m Dr Kat Arney, I’m Buddini’s colleague from the science communications team at Cancer Research UK. So if we kick off and start with you Kathryn, because this is your area of expertise – you’re someone who studies how things in our diet are linked to cancer. How do we actually go about finding that out, how do you figure out what in all the different kinds of things that people eat actually increase the cancer risk and how do we know that this sort of research is reliable?

Kathryn: Most of the knowledge we have about diet and cancer comes from these large population studies. So typically we recruit hundreds of thousands of people from the general population and we ask them questions about their diet and about their lifestyle. And then we follow them up over many years to see who develops cancer. And then what we do is we look back and if we’re talking about meat, for example, we’ll look back at the people who said they ate quite a lot of meat and compare them to the people who said they ate less meat and then we’ll look at how many cases of cancer occurred in both of those groups of people and then we can calculate the risk of cancer.

Kat: This is about risk isn’t it? It’s not about saying “OK, you ate meat so you did get cancer, you didn’t eat meat so you didn’t get cancer”?

Kathryn: No, so we group people into categories and then we look at in each category how many cases occurred and then we look at the risk from that. I think that the main issue with these types of studies is that people who eat a lot of red meat for example, or a lot of processed meat, they’re also more likely to smoke, to drink alcohol, more likely to be overweight, less likely to exercise. So these things also will give them a higher risk of getting cancer so it can be a bit difficult to see whether they have more cancer, there are more cases of cancer in this group, it’s bit difficult to see whether it’s actually the meat itself or these other lifestyle factors. So when we analyse the data we’re very careful to try and make sure that we take these other lifestyle factors into account, just trying to look at the effect of meat on cancer risk, although it can sometimes be hard to completely rule out these other factors.

Kat: And the terms of the reliability of the studies, you think well, what did you eat 20 years ago? How do we know that these kinds of studies are actually giving us reliable information about people’s diets?

Kathryn: In a lot of the studies for the questionnaires on people’s diets a lot of care was taken in the questionnaire, the way it was used to make sure that is a valid tool and it really is assessing what people eat. In some of the studies – it varies bit from study to study – but in some of the studies the diet information we ask them is not just the start of the study, but numerous time points throughout so that information is updated as we go along as well.

Kat: So you’re not asking people to remember what they had for breakfast five years ago, it’s what are you eating now?

Kathryn: Yes, so at the start of the study we ask them what they’re eating at that time, and then we look forward and follow them through time so we have to wait many years for cases of cancer to develop, so it doesn’t rely on people’s memory.

Buddhini: Not all meat is created equal right? So what exactly do we mean by red meat and processed meat? And what about chicken and fish? Where does that come in?

Kathryn: So red meat is beef, lamb and pork, these are red meats. There are other meats that we don’t eat much of the UK like goat or horse meat – not intentionally, anyway – and those are also counted as red meat. And then processed meat, that’s meats that have been salted or cured or had preservatives added or smoked. So they’re things like bacon, salami, pastrami, ham, sausages, beef jerky. And one of the confusing things when I’ve been talking to people is that they think that minced pork or minced beef is processed, but actually if you just buy that from supermarket it’s not – it’s red meat. It doesn’t matter that it’s been minced up, it just counts as red meat.

Buddhini: And does it matter how the meat is actually cooked?

Kathryn: Yes, Owen might talk a bit more about this, but in terms of the mechanisms of how it might cause bowel cancer in terms of barbecuing or grilling at high temperatures there are some compounds that can form which might be important.

Kat: In terms of meats – red meat, processed meat particularly – what sort of scale of risk are we talking about for these types of food? For example will one bacon sandwich increase your risk by a lot? What sort of scales are we talking about?

Kathryn: The World Health Organisation, when they did their recent summary of all the evidence, what they summarised was that an extra 50 grams of processed meat a day -which is about two rashers of bacon, what you’d have in a bacon sandwich or 1 to 2 slices of ham – they said that an extra 50 grams per day increases your risk of bowel cancer by 18 per cent.

Kat: Is that a lot? Is 18 per cent a lot? Owen, do you have something to add here?

Owen: If you say 18 per cent that might sound quite a lot as an individual value but if you think about in terms of a relative risk it’s still relatively small. So we’re not talking about a massive increase in risk, which is why there’s been so many studies over the years that have said is it or isn’t it bad? It’s just because it’s a small increase in risk is the problem really. It’s taken us a while to work it out.

Buddhini: And I guess it doesn’t help when you get difficult-to-interpret press releases from the World Health Organisation that fan these fires of misconception. So what do we mean by definite and probable? Because that was really interesting – bacon is definitely bad, burgers are probably bad? What do we mean by that? And they compared it to tobacco, which is definitely a cause of cancer – is it as bad as tobacco?

Kathryn: I did see a lot of misleading headlines – now bacon is as bad as smoking! – which isn’t really right. So what the World Health Organisation does is that they put components or things like tobacco and processed meat into categories. So what they’ve said is processed meat is group 1, which is the same category as tobacco. And that means that they concluded when they summarised the evidence that there is enough evidence to say that it does cause cancer in humans. But with red meat there is a bit more uncertainty, so it’s in group 2A, in that it probably does cause cancer. In terms of comparing tobacco and processed meat, what we know is that they’ve said that they both do cause cancer, but the level of risk is much greater for tobacco. So we estimate that about 20 per cent of all cancers in the UK are caused by tobacco smoking, whereas about 3 per cent are caused by red and processed meat – that’s our estimate. And if you look at the number of cases of cancer a year, if you look at it this way, if no one in the UK smoked we think we would prevent about 65,000 cases of cancer, whereas if no one ate red or processed meat we think we would prevent about just under 9,000 cases of cancer a year.

Kat: That’s still a reasonable number, but I think what didn’t come across in the news stories was that is the strength of the evidence that people are talking about rather than the size of the risk, wasn’t it?

Kathryn: Exactly, yeah. So they look at whether there is enough evidence that something does cause cancer – it doesn’t matter by how much. So that’s why processed meat and tobacco are in the same group.

Kat: So moving on bit, Owen – we heard all the stories that bacon will increase your risk of cancer. What kinds of cancer are we talking about, because there are many different types of cancer?

Owen: There are many different types of cancer and really the best evidence is for bowel cancer. There’s a little bit of discussion and if you look at the studies there’s a little bit of evidence that there might be an increased risk of prostate and pancreatic cancer, and with processed meat a little increased risk of stomach cancer, but predominantly all the evidence is in bowel cancer and I think the other studies are still relatively small in those other tumour types, which is why the WHO did clarify that it’s really bowel cancer that we’re talking about here.

Kat: I did see a study last year that was looking at the link between red meat and breast cancer but I think that link didn’t really stack up did it?

Owen: No, and I think that if you look across the literature there are many different studies pulling out many different risks and they can be quite different, and that often relies on the size of the study and when and where they were done. So I think we can say that for red meat and processed meat, the links really are with bowel cancer and not with any other cancers. Does Kathryn agree with that?

Kathryn: Yes, I think, definitely. You’ll find that there is a study about red meat and almost every type of cancer, but the evidence really is for bowel cancer – there’s a lot of studies on bowel cancer and red meat and they do generally show the same story, especially when you put them together.

Buddhini: Owen, I’m really curious about the mechanism, because how does red meat cause cancer? What’s going on in the cells lining our gut?

Owen: I think the thing here is just as we know that there is only a slight increase risk with red meat and bowel cancer, one of the things that does mean is that when you try and understand the reasons why red meat causes bowel cancer, it’s that it’s very difficult to really pull out exactly why. So if you think of your bowel, it’s an amazing tissue which turns over every 3 to 5 days and your tumour cells have to hold on. And also your bowel is then exposed to many different carcinogens, so what is thought in terms of red meat and processed meat is that you can increase basically your chance of carcinogens – these N-nitroso products – these can cause mutations to DNA and probably might cause more mutations in some of the key colon cancer tumour suppressor genes. So there’s also roles for haem iron which is also in red meat, this is been shown to be damaging as well.

Kat: This is the chemical that’s in blood that captures the oxygen, that’s the iron component of the blood?

Owen: Yes, so there has been some suggestion that the high levels of that can be bad for the bowel. And then there are other discussions such that generally higher levels of iron generally might be bad cause DNA damage and cause mutations. And then the other thing that people have suggested is that we now know in our intestines there are many different bacteria, so therefore what you eat could easily change types of bacteria…

Buddhini: This is the microbiome link with cancer?

Owen: Absolutely. So there are a whole number of mechanisms which it can be, and you can go through and read papers, there are many different studies saying this component or that component. So again I think most people if you are going to go for the most evidence would be discussing about the haem iron or the mutagens in the meat, in the processed meat, but really there’s still a lot to learn. If you just have small increase in risk, it’s not as easy to work out as tobacco for example.

Buddhini: You talked about tumour suppressor genes. So these are genes that normally prevent cancer, but when mutated that means they can no longer prevent cancer, so cancer happens. Can you talk a bit more about that?

Owen: So within the intestinal epithelium there is one key tumour suppressor called APC – this is the adenomatous polyposis coli gene. So patients that have one copy of this faulty gene will all develop bowel cancer, and then just as cancer sporadically occurs, you get mutations in this gene, and this gene is thought to be very important for the very early initiation of colon cancer. It is a very large gene and there are lots of places where mutations can happen. So anything that causes an increase in the mutations in this gene – let’s say some mutagens in the colon hitting that gene – will predispose you to cancer. When we’re thinking about something such as an increase in risk, we’re generally thinking an increased chance of cancer initiation, rather than cancer progression. Although I would say we really need to work that out little bit more, but we would say probably that this has caused an increase start of cancer, and if you increase the chances of starting cancer you then increase the chances that the cancer will progress.

Buddhini: It’s also important to understand how bowel cancer starts because that means you can develop better tools to catch it early, and early diagnosis is a big part of bowel cancer cures.

Owen: Absolutely and also in terms of screening. If you do have an agent that increases your risk of cancer, if you catch it early – and we now have the test in the UK to check for bowel cancer – then you can just cut out those small early lesions and your risk then goes back to the same risk as the general population, so I think that’s the other thing to say that although we may be increasing risk there’s a lot of things we can do to stop this and overcome this risk.

Kat: That’s what I wanted to ask. Perhaps Kathryn, you talked about how many cases of cancer we could avoid in the UK if everyone just stopped eating red and processed meat – but bacon tastes good, some people are vegetarians they still get cancer, some people eat lots of meat and they don’t get cancer. But what is the best advice to people to cut their cancer risk from red and processed meat? Is it better to not eat a tour?

Kathryn: I think you’ve hit on some things that people eat not just for health reasons. There’s a lot of things to take into account – what they like, obviously, whether they’re willing to give up bacon sandwiches, the price of food, what their family will eat. So there’s lots of reasons why people do or don’t want to eat meat. So if you think about how much processed meat you eat, if it’s every day or nearly every day it’s a good idea to think about cutting down.

Kat: We have evolved to eat meat – because I know there are some people who say we shouldn’t eat meat at all – but as a species we have evolved eating red meat, certainly. Maybe not bacon, but definitely meat. How does that fit into the picture, given that we do need sources of protein?

Kathryn: We do need to eat protein, our body does require it, but if you actually look at how much protein people on average are eating in the UK, they’re actually eating more than our bodies need. So I don’t think generally people in the UK need to worry about getting enough protein. Their diets usually contain a lot more protein than they need.

Kat: Owen you talked about some of the mechanisms by which some of the components of meat, some of these chemicals, the iron, maybe these DNA damaging molecules might increase the risk of cancer. Are there any ways perhaps the effects of those chemicals could be reduced? I’m thinking for example breast cancer we have some drugs like Tamoxifen that reduce the amount of oestrogen in the body and helps breast cancer risk by reducing that female hormone. So is there anything similar on the cards for bowel cancer and some of the products in meat?

Owen: I suppose there’s always been that discussion and Kathryn can come in on this that some of the earlier studies suggest that if you eat high fibre that can neutralise many of the effects of high red meat, high haem. So we can also think the idea of a balanced diet – although it’s not as targeted as trying to do Tamoxifen there is evidence for that. And there is also good evidence that in terms of aspirin and some of the vitamin D that there are also links in terms of colon cancer risk there, so we have to put this in the context of other studies. One of the other interesting things is that we’re also starting to learn that individual people’s risks might be different depending on their DNA, so therefore they may carry other changes that might make them either more or less risk. So what we’re talking about here is a population risk rather than an individual risk.

Buddhini: Moderation and a balanced diet is so much more boring than miracle antioxidants.

Kathryn: I would agree with Owen that generally the population studies, especially when you pull them together and look at them altogether, they do tend to show that if you have eat lots of fibre that is associated with a lower risk of bowel cancer, so that’s one thing on the protective side I guess. If you eat lots of whole grains, oats and wholemeal bread then that might help you reduce your risk.

Buddhini: How exactly does that work, what’s the mechanism of that?

Owen: People are still trying to work that out. With high fibre you change your bacteria in the gut, and again you’re thought to have better bacteria that then break down [food] and cause less damage. And there’s also data about how quickly – imagine that if your intestinal epithelium, your small intestine in your bowel, is like an epithelial escalator, anything that increases the time or quickens cells falling off might stop cancers holding on, so there’s a lot of work that decreasing transit time and how long things sit within the bowel decreases risk so having regular movements might be good but there’s a whole science behind it.

Kat: Without wishing to be too graphic – it is nearly teatime – but there is some pretty nasty stuff in the end products of what your food turns into and I can’t imagine that stuff hanging around on the cells is particularly good for them.

Owen: There is evidence, and Kathryn probably knows better, that your transit time seems to be fairly important.

Kat: One of the things that is always difficult to talk about when we talk about diet and cancer risk is that everyone has to eat. We don’t have a choice necessarily in not eating like there is with smoking – you can choose to smoke or not to smoke – but then a lot of the information in some of the papers comes out about very isolated things. How do we start to piece together all the information about all the different components of the diet? Are there studies that are really starting to pull that all together? Kathryn?

Kathryn: I think that in terms of looking at all the evidence one of the most important things to think about is that tobacco outweighs everything else in terms of cancer risk. So if you smoke it is definitely a good idea to focus your efforts on trying to give up smoking. In terms of diet, yes there are headlines that come out saying coffee is good you, something else is bad for you, and it is hard to figure out are these things just one isolated study that found something that has been picked up by the media, or is it something a lot of studies have found? I think with the World Health Organisation, what they have really done is summarised all the available evidence and really concluded that there is a small increased risk of cancer with processed meat, so I think that is probably why it’s got a lot of media attention as well, because it really is looking at all the evidence together.

Buddhini: Based on that, what do you think a healthy lifestyle looks like? We know that four out of ten cancers are linked to preventable causes, so what can a person do to minimise the risk of cancer – be that diet and any other factors. How do we think it all links up?

Kathryn: I think if you smoke definitely stop smoking. That would have a big effect on your risk of getting cancer. And even if you give up before you’re 40 you actually have a little bit more of a risk of cancer than someone who’s never smoked, but you really do reduce your risk of getting cancer. The other thing is trying to be a healthy body weight. So if you’re really overweight that increases your risk of quite a few different types of cancer. If you’re a woman it increases your risk of postmenopausal breast cancer but also other cancers and for men as well. So stopping smoking and trying to make sure you’re a healthy body weight are the two important things. And then in terms of diet, I would say cutting back on processed meat, making sure you have a high fibre diet, plenty of variety.

Owen: It’s kind of the boring balanced diet stuff. There’s no superfood that’s going to help you balance out the bacon.

Buddhini: I’m curious because it’s coming up to Christmas season as well, what role does alcohol play, and does it compound the issues of red meat and bacon risks?

Owen: So there’s been in terms of some certain cancers you can find that I think for pancreas, drinking and smoking is bad together. So I think there are certain things, but again alcohol is also a risk factor and if you look at the World Health Organisation website it is a proven risk. So again moderation is important.

Kathryn: Alcohol does increase your risk of breast cancer, and also cancers of the oral tract, the throat and so on. So moderation with alcohol as well.

Buddhini: We’re removing all the fun!

Kat: Moderation doesn’t necessarily kill fun. We’re running out of time now, I just wanted to ask each of you, Owen and Kathryn, if you had any final comments, closing thoughts or maybe where you think the future of this kind of research is going to go. Starting with Owen.

Owen: I think we still as I say have a small relative risk and we’ve still got to understand a lot better how red meat causes cancer, and I think if you then start understanding which components of it does affect cancer and which is the carcinogenic part we can then start putting these risks into a proper context and then we can start understanding what we can do. A lot of the – not that it’s pseudoscience, because there’s a lot of science behind it – we’ve been very good at studying mechanisms of other processes, but things that affect epidemiology, things that affect risk, we probably haven’t studied them in quite so much depth before and I think that’s one of the things that as a community we need to start doing.

Kat: Kathryn, what’s the future for you?

Kathryn: I do work on large population studies but I’m actually thinking that for the meat I agree completely with Owen that we really need to know more about the mechanisms, we really need to understand what it is about the meat. So the population studies are fairly consistent in that they do tend to show especially when you look at them all together that eating processed meat increases your risk of bowel cancer, but we really do need to understand what it is exactly. Is it the iron? Is it the nitrates, the preservatives? Is it cooking them at high temperatures? Or is a combination of all these things? I think that will really help us and I think that is really important. And I think in general looking at diet and cancer, more of this getting all the studies together, summarising them altogether, and then you generally do get a clear idea of what is associated with cancer.

Kat: Thanks very much so we have lots of information about diet and cancer and risks and red and processed meat and all these kind of things on the Cancer Research UK blog and on our website, and we have been live tweeting some links to those (I hope my colleagues have been!). I like say thank you very much to our guests that’s Owen Sansom from Beatson Institute in Glasgow, Kathryn Bradbury from the University of Oxford, my colleague Buddhini Samarasinghe from Science on Google+ and I’m Kat Arney. I’d like to say thank you very much for watching. We would love to know your ideas for what you would like us to discuss. We have access to some absolutely incredible experts across the UK and perhaps even further afield talking about the latest cutting issues in cancer, in cancer prevention, in cancer research and cancer treatment. So please do drop us a message under this video – let us know what you’d like to hear about. So thank you very much for watching and I wish you a very pleasant evening or day – enjoy your bacon sandwich!

Buddhini: With caution and in moderation! Thanks for joining us and goodbye.