Diet, lifestyle and breast cancer
By Dr Shireen Kassam
Cancer in general shares common features. There are 3 main stages of cancer development – initiation, promotion and progression. Damage to cells and DNA occurs all the time during the phase of initiation. However, the body has an amazing capacity to correct this damage or remove the damaged cells. Some cells will linger and if given the correct growth environment they will start to divide and increase in number during the phase of promotion, with some becoming cancerous. At a certain point, these damaged and cancerous cells gain the ability to travel around the body away from their site of origin and lodge in other organs – progression.
The main opportunity to prevent cancer is during initiation and promotion, when we can help the body avoid damage to cells and prevent these damaged cells from surviving, dividing and becoming cancerous. Factors that contribute to cells becoming damaged and cancerous include, low grade chronic inflammation, an unhealthy gut microbiome, increased levels of growth hormones and an immune system that is not functioning adequately. All these adverse factors can be prevented or modified to a significant degree by adopting healthy lifestyle behaviours as outlined in the World Cancer Research Fund (WCFR) guidelines on cancer prevention.
Important lifestyle factors for preventing breast cancer
Be a healthy weight: Being overweight or obese is a significant risk factor for developing breast cancer. Although the determinants of body weight are complex and multi-factorial, diet and lifestyle factors are very important. People eating the most plant foods and lowest amount of animal-derived and processed foods tend to maintain a healthier body weight. On a basic level, we all eat the same volume of food everyday – around 4 pounds. The easiest way to maintain a healthy weight is by choosing foods that are low in calories but high in nutrients thus paying attention to the calorie density of foods.
The good news is that if your weight is higher than it should be but you successfully lose weight, you can significantly reduce your risk of breast cancer. Unfortunately, if you are overweight or obese and do develop breast cancer, treatments seem to be less effective and the chances of surviving are lower.
Eat more fruits and vegetables: Eating more fruit and vegetables is a good way of reducing the risk of cancer in general and specifically breast cancer. Aim for at least 10 portions a day (800g). Including cruciferous (kale, cabbage, broccoli, cauliflower) and yellow/orange vegetables (high in carotenoids) may be particularly beneficial, but overall you should aim to eat a wide variety of colourful fruits and vegetables.
Increase fibre in the diet: Fibre is an essential and hugely beneficial component of the diet, yet less than 10% of adults in the UK meet recommendations for consuming 30g per day. Fibre is only found in whole plant foods i.e. fruit, vegetables, whole grains, beans, nuts and seeds and these foods should make up the majority of the diet. There is a consistent association between fibre consumption and a lower risk of breast cancer. Diets high in fibre are associated with a healthy gut microbiome, improved immunity and lower level of inflammation.
Eliminate processed and red meat: In 2015, the World Health Organisation classified processed meat as a group 1 carcinogen (causes cancer) and red meat a group 2a carcinogen (probably causes cancer). This classification was based on data related predominantly to the risk of colorectal cancer. However, processed and red meat consumption is also associated with an increased risk of several other cancers, including breast cancer.
Limit consumption of ultra-processed foods: There are emerging data on the link between the consumption of ultra-processed foods, sugar-sweetened beverages and cancer. Studies suggest that ultra-processed foods may increase the risk of cancer and in particular breast cancer. One study showed that for every 10% increase in the amount of ultra-processed foods in the diet, there is a 10% increase in the risk of developing breast cancer. The mechanism by which these foods increase cancer risk is not entirely clear, but it is likely a combination of factors, including the presence of food additives, contamination from plastic packaging, the lower quality of these foods (low in fibre and high in salt, sugar and fat) and the fact that they displace healthier, whole foods from the diet.
It should be remembered that not all foods meeting criteria for being ultra-processed are considered unhealthy. Most of the adverse health impacts are associated with the consumption of processed meat, sugar-sweetened beverages and foods that are high in saturated fat, sugar and salt (cakes, pastries, fried snacks). Some foods considered ultra-processed, such as whole grain breads and cereals, are associated with health benefits.
Swap cow’s dairy to soya milk and foods: The link between dairy consumption and breast cancer risk is complex. Intuitively you may think that dairy would increase the risk of breast cancer as it is high in saturated fat, cow’s oestrogen and growth hormones such as IGF-1. However, this is not the case in every study. What does seem to be more certain is that replacing cow’s dairy for soya milk and foods can reduce the risk of breast cancer. In general, regular consumption of soya can reduce the risk of breast cancer by around 13%. Swapping dairy milk for soya milk could reduce the risk by up to 32%. It might be important to start soya consumption in childhood and adolescence to reduce the risk of developing breast cancer later in life.
Healthy diet patterns: It is more useful to consider the whole diet rather than the individual components. The consensus from the WCRF guidelines for cancer prevention is that a healthy diet is one that is composed predominantly of whole plant foods – fruits, vegetables, whole grains, beans, nuts and seeds – and may contain some fish and low fat dairy. But avoids/limits red and processed meat, ultra-processed foods in general and sugar-sweetened beverages. This sort of plant-based dietary pattern may reduce the risk of breast cancer by around 11%, with some but not all of the benefit due to improved body weight and adiposity. It’s worth noting that diet quality matters, with healthy plant-based diets centred around whole foods, rather than more processed plant-based foods, are associated with lower rates of breast cancer, including more aggressive forms.
Be physically active: Regular physical activity has so many benefits for health, including cancer prevention. For breast cancer, regular physical activity could reduce the risk by at least 13%, and the more active you are the better. Regular exercise shares all the benefits of a healthy diet, including helping to maintain a healthy weight, reducing insulin resistance, lowering oestrogen and IGF-1 levels and reducing inflammation, turning off cancer promoting genes and improving the function of the immune system.
Avoid alcohol: Alcohol is a group 1 carcinogen (it causes cancer) and probably contributes directly to around 5.5% all cancers globally each year. The link between alcohol consumption and breast cancer is particularly strong. A large, observational study of 105,986 women suggested that drinking three to six drinks per week increased the risk of breast cancer by 15% compared to women who did not drink. Even ‘light’ drinking (0.5 drinks/day) was found to increase the risk of breast cancer by 9%.
Diet and lifestyle after a diagnosis of breast cancer
It’s never too late: Changing lifestyle behaviours can be hugely beneficial even after a diagnosis of breast cancer. Adhering to the WCRF guidelines can significantly reduce the risk of cancer recurrence and improve survival, with greatest benefits seen from avoiding smoking, regular physical activity, eating plenty of fruit and vegetables and limited consumption of sugar-sweetened beverages. In one of the largest nutrition intervention studies of all time, women who developed breast cancer and who were eating a reduced fat diet with increased amounts of fruit, vegetables and whole grains had a 21% reduced risk of dying from breast cancer compared to those who had not changed their diet. Similarly, women who undertake regular physical activity after breast cancer could reduce their risk of dying by up to 40%.
There are limited intervention studies in people receiving treatment for breast cancer. One study in people with breast cancer undergoing chemotherapy randomised women to a home-based diet and exercise intervention, in line with the WCRF guidelines, or to continue usual care. The dietary intervention supported participants to adopt a more plant-based diet and minimise alcohol consumption. The results showed that women in the intervention group were more likely to achieve a pathological complete response.
In general, plant-based diets may improve outcomes after a diagnosis of breast cancer with soya and green tea being particularly beneficial additions to the diet. Ensuring adequate vitamin D intake is sensible. Although it is not clear that drinking alcohol after a diagnosis of cancer impacts prognosis, there are plenty of reasons to avoid drinking, including adverse effects on cardiovascular health and brain health.
All six pillars of lifestyle medicine are important after a diagnosis of breast cancer. For example, all forms of stress can adversely affect prognosis due to negative impacts on the immune system and may explain some of the differences in cancer outcomes between different ethnic and racial groups. Some integrative approaches, such as acupuncture, mindfulness-based activities, yoga, reflexology, may also be useful for managing common symptoms including pain, anxiety and depression and fatigue.
Preventing chronic conditions and second cancers
People with cancer have an increased risk of cardiovascular diseases and type 2 diabetes and an increased risk of a second primary cancer. This can be a consequence of the cancer itself or its treatment. Focusing on healthy habits can reduce these risks significantly.
There are many benefits of adopting healthy habits for reducing the risk of breast cancer and for improving cancer-related outcomes.To get started on your journey of a healthy diet and lifestyle, check out our Plant-Based Eatwell Guide. For those with a diagnosis of cancer, read our factsheet on lifestyle strategies.
Footnote: It goes without saying that smoking tobacco causes cancer. Breast cancer is no different. Never smoke cigarettes.