What do we know about cancer?

I have spent today in Sheffield at the Nutrition Society’s Cancer Networking Conference. A fascinating day bringing together molecular scientist, behavioral change experts through to cancer surviving lobbyists to present their research and opinions to form a cohesive picture from across a wide range of expertise of what to do.

What is known irrevocably is that following healthy dietary patterns and being a healthy weight reduces the risk of cancer. The obesity message is being shouted very loudly by Cancer Research UK in their recent campaign – OBESITY causes cancer. But why are people not taking notice? For example, only 1/3 of people in the UK eat 5 portions of fruit and vegetable a day. Over half of the UK population are overweight or obese. Behavioral change is complex, but here I am focusing on two elements – knowledge and environment. Information to build knowledge is widely available on diet and cancer risk if people choose to look for it, however on diagnosis of cancer nutritional advice from experts is sparse. It is on diagnosis that people are most receptive to making change. Very few people are referred to a dietitian and due to limited resources patients with wasting cancers tend to be the only ones given appointments. On average a cancer unit has 2 minutes per year of dietitian’s time per patient; this gets pooled and given to who are perceived as the neediest. Whilst important that patients with wasting cancers are provided with dietetic support, overweight patients with metabolic cancers would also benefit. So, there is still some work to do on building knowledge at the time a person is most receptive to change. But why is the information that is widely available not being implemented? Behavioral experts are pointing very hard at the environment i.e. availability of processed food, the amount of sugar in foods, advertising, cost of healthy food vs unhealthy food. Cancer Research UK launched a campaign in the Westminster area last year aimed at lobbying MPs for changes in the UKs obesogenic environment. It has been successful with 23% of MPs in February 2018 being aware of the link between cancer and obesity to 48% being aware in March 2019. Cancer Research UKs message is that overweight and obesity causes cancer, but this is a societal problem not an individual problem and needs to be tackled as such.

Being overweight and alcohol intake above recommended levels increasing the risk of cancer have sound evidence backing these messages. But as can be seen from the table at the link below beyond that evidence is lacking and this is the problem, practitioners do not want to give advice that is not evidence based, so they say nothing. The table found at the link was produce in 2018 by World Cancer Research and the American Institute of Cancer research summarising evidence on the relationship between different cancers and diet. Red and orange show increased risk and green decreased risk. Note though how many gaps there are which means there is no evidence either way and also that findings are different across the cancers.

Once diagnosed what can influence the outcome? Firstly, receiving the full recommended dose of chemotherapy. Obese patients receive reduced dosages of chemotherapy due to the associated risks. I did not know that! And patients that receive >85% of full dose have better outcomes. Also chemotherapy has better outcomes in patients with lower body fat and high lean body mass (muscle). The importance of muscle mass was mentioned a number of times during the day including in a discussion on whether patients should undergo pre – hab before treatment. Pre hab being muscle building exercise and nutrition intervention designed to remove deficiencies. Undernourished patients are two times more likely to get chemotoxicity and spend 2 days longer in intensive care after surgery.

Weight (fat) loss during treatment for overweight patients has been proven to improve outcomes in breast cancer with a 24% reduction in new and recurring cancers after 5 years and 16% reduction over 19.6 years. There is some evidence emerging that the 5:2 diet maybe particularly effective, timing the low days with treatment. There is still much work to do in this area before any conclusion can be formed but findings from a rat study (but none in humans) found that fasting can reduce the toxicity of chemotherapy to healthy cells and provide more targeted treatment to cancer cells. But fasting is not for everyone and patients need to do what they can to get through treatment, weight loss using any healthy method is beneficial.

When it comes to nutrients there is confusion. Cancer treatment changes metabolism and what is thought to reduce the risk of primary cancer is struggling to be proved after cancer and in preventing secondary cancer. It is also known that people with certain types of cancer are more likely to be deficient in certain nutrients suggesting that not being deficient reduces risk, but this is not always the case. For example, vitamin D deficiency is seen more commonly in some cancers but supplementing a cohort has not resulted in these groups getting less cancer. Plus how much to give; vitamin E is thought to be cancer preventative but too much is thought to be cancer causing. And what happens if just looking very narrowly at the outcomes of supplementing? Supplementing with vitamin E has 947 metabolic factor changes – it affects 947 things, and what do they then affect? Research is just not there yet.

Everyone is individual and reacts differently, for example insulin resistance reduces the effectiveness of chemotherapy. Research in gut microbe and cancer is increasing and links are starting to be made but a recently study published found that giving a group the same diet aimed at making the same changes resulted in different gut microbes, because everyone is different and metabolises differently. Therefore, advice needs to be personalised depending on an individual’s response. Then dietary advice is different for different cancers. It’s complicated and resources are not available within the NHS for such personalised advice.

In summary there is a massive unmet demand for information; patients are frustrated, they want nutritional advice from experts but are not getting it. Practitioners do not have robust scientific evidence to base advice upon. Cancer preventative lifestyle recommendations that are evidence backed are not being implemented by the general population and often by patients after diagnosis highlighting the need for support in behavior change. Also, everyone is individual, responding differently to diet and treatment. It is a blurry picture. There are some strong takeaway messages; being a healthy weight, following a balanced diet and exercising regularly is beneficial. And that experts from different fields are starting to talk, share knowledge and are starting to put the pieces of the jigsaw together to create a complete picture. There is hope.