Q&A follow up – A closer look at: diet and mouth and gastrointestinal cancers

Thank you to everyone who attended our recent live webinar on diet and mouth and gastrointestinal cancers, run in collaboration with World Cancer Research Fund. Below are the responses to the questions posed by the audience during the live event that we did not have time to answer. We hope this is a useful resource and once again extend our thanks to our attendees and our speakers, Bridget Benelam (British Nutrition Foundation), Susannah Brown (World Cancer Research Fund International) and Rachel Clark (World Cancer Research Fund), for their time.

For the World Cancer Research Fund top 10 Recommendations, why is tobacco only given such a passing mention?

Rachel: World Cancer Research Fund specializes in the links between diet, weight and physical activity and cancer. We fund research into these areas and raise awareness of global research findings. We don’t include smoking prominently in the 10 Recommendations because this isn’t an area we specialize in, but we do always mention it.

We also know that most people are now aware of the link between smoking and cancer, but there are still gaps in knowledge when it comes to the other lifestyle risk factors. One of our aims is to make people as aware of these other lifestyle risk factors as they are with smoking.

However, we realize that quitting smoking is the most important thing people can do to reduce their risk of cancer, and we are planning to talk about it more often so that we give people the full picture when it comes to risk. We have started to take steps towards this and have just published this webpage, which looks at all the different lifestyle risk factors.

5% of bowel cancer cases could be prevented with lifestyle changes around red meat consumption, is that a UK statistic?

Rachel: Yes, all the statistics in my presentation were UK stats. You can find all our UK preventability statistics here.

You mention the amount of time carcinogenic materials are in contact with the lining of the bowel. Does this mean that if an individual holds onto feces instead of going to the toilet they have an increased risk of bowel cancer?

Susannah: The studies we analyze do not collect this type of data so we cannot investigate a link between time feces is in the colon and risk of colorectal cancer; however, we do know that the longer you hold the stool in your colon, the more water is absorbed and the harder it becomes meaning it could potentially cause colon damage due to the effort and strain of expelling it later on. As you noted, by not going to the toilet, waste materials will be in contact with the bowel for longer than necessary and while we don’t have data looking at this relationship we would recommend people to visit the bathroom as and when they need to and can.

Some interesting information on colorectal cancer is available here.

And all our findings from our Continuous Update Project can be viewed here.

You mentioned that sausages from the butchers would not be classed as processed meat, what about ones from the supermarket e.g., Wall’s?

Rachel: Processed meat has been smoked, cured or had salt or chemical preservatives added rather than having just been cooked or reformed (like most sausages and burgers). This includes bacon, salami, chorizo, corned beef, pepperoni, pastrami, hot dogs and all types of ham.

Wall’s sausages would be classed as red meat as they haven’t been processed by smoking, curing, salting or by adding chemical preservatives. One way to check if shop-bought sausages count as processed meat is to look for Nitrites or Nitrates on the ingredients list. This would count as processed meat.

Have you looked into any possible link between simple sugars and cancer risk?

Susannah: As part of our Continuous Update Project we look at the components of diet, weight and physical activity that may increase or decrease the risk of cancer. Sugar is one of the risk factors we look at.

Currently there is no strong evidence to link sugar directly with cancer risk. It is challenging to capture the data partly because of the inconsistency of the classification of sugars – sometimes ’sugar’ is equated with sucrose, which has been the chief sugar in human diets, but now is less so, and some studies investigate only ‘packet’ sugar purchases for use in the home; this is in general a relatively small and diminishing proportion of total sugars consumed as now much of people’s sugar consumption is from food that has it added to it. However, we do know that having a lot of sugar in our diets can lead to weight gain, and being overweight increases our risk of cancer. Being overweight or obese increases the risk of 11 cancers (more information can be found here)

In 2015, the Scientific Advisory Committee on Nutrition, advised sugar intake should be drastically reduced. Consuming foods high in sugar is likely to push people in to positive energy balance (this is where they are consuming more calories than they are expending and are likely, over time, to put on weight).

You talked about the 30g fiber per day recommendation and the importance of having both sources (insoluble and soluble) – is there a ratio that is beneficial? 

Rachel: The research on fiber and bowel cancer looked at total dietary fiber rather than its subgroups, so we don’t know if there is a beneficial ratio. We know that the more fiber the better for reducing bowel cancer risk and that people should aim for 30g a day. You can read our full report on bowel cancer here – page 8 looks at the evidence on fiber and bowel cancer risk.

As a lot of the evidence is based on association, can we assume causation? As the 10 steps seem very definitive i.e., AVOID alcohol for cancer prevention.

Susannah: As you correctly noted we use observed associations from epidemiological evidence; however, as discussed in the webinar, for a link to be considered ‘strong’ and for the picture to be more complete, there must also be evidence for plausible mechanisms that explain how something might be causing or preventing cancer. This usually comes from animal or experimental studies. The appendix in all our published reports details the criteria for grading the evidence (see pages 5659 of the esophageal cancer CUP report).

For a judgement of ‘strong evidence’ (convincing or probable), the evidence must demonstrate a causal association and therefore can be used to inform the recommendations where guidance is given.

I think the healthy living plate is a helpful visual aid but I wonder as eating habits change to more rice- and pasta-based meals whether it will become less relevant?

Bridget: I’m assuming that your question relates to the fact that rice- and pasta-based meals tend to be composite foods including a number of food groups together, rather than a traditional British ‘meat and two veg’ type meal where the food groups are separate and perhaps more easy to identify? I agree this is a challenge in communicating the Eatwell guide but I think the messages about balancing food groups, as visualized in the Eatwell guide, remain relevant. They key issue is to provide information so that people can identify the key food groups within a composite dish so that they can relate this to the messages on the Eatwell guide and to the balance of the diet overall. We have some information about linking the Eatwell guide messages with composite dishes on our website.

Rachel, following on from the question about alcohol and smoking, is that same process involved if you, for example, consume alcohol and then follow it with some processed meat (e.g., a bacon sandwich?). Is it worse if alcohol is involved?

Rachel: As mentioned in the webinar, smoking and drinking alcohol together is more harmful because alcohol may function as a solvent, enhancing penetration of other carcinogenic molecules into mucosal cells. We know that alcohol and smoking both increase the risk of mouth, pharynx, larynx and esophageal cancer.

When it comes to processed meat, we don’t have any evidence on its interaction with alcohol. Processed meat is linked to an increased risk of stomach and bowel cancer and it is the digestion of processed meat, rather than its direct contact with mucosa cells, which may increase our risk of these cancers.

You can read the full reports for stomach and bowel cancer here:

Do you have evidence regarding vitamin D and gastrointestinal tract cancers/other cancers?

Susannah: With regards vitamin D there is limited evidence to suggest it may decrease colorectal cancer but more research is required in this area and we do not have enough evidence to make any recommendations. Vitamin D is complicated exposure to look at as it is challenging to measure intakes from foods and even when looking at the biomarker we know that plasma/serum vitamin D status can be influenced by sun exposure, obesity, seasonality, smoking, and measurement error. We haven’t seen any other cancers associated with vitamin D.

As correctly noted by you we don’t have a recommendation specifically for oily fish. This is because we haven’t seen strong links between fish intake and cancer risk. We do recommend that for those who eat meat, the amount of red meat consumed can be limited by choosing poultry and fish instead. Oily fish are  source of retinol and vitamin D and contain important long-chain unsaturated fatty acids and so are important as part of a healthy, balanced diet.

Do you provide certificate for CPD?

Rachel: We don’t provide a certificate for the webinar as there was no formal assessment. However we do provide a certificate for our online cancer prevention training which is free for health professionals. You can access the training as part of our free cancer prevention package here.

Do you agree with these responses, or have additional insights? Please share your comments below. Also, you can view the webinar on demand at your leisure.