By Rachel Clark, Health Promotion Consultant, World Cancer Research Fund
In recognition of Breast Cancer Awareness Month this October, we’ve invited Rachel Clark from the World Cancer Research Fund to explore recent evidence related to dietary patterns and risk of breast cancer. The blog delves into key findings from a recent study, highlighting a reduced risk of post-menopausal breast cancer in vegetarian and vegan women, while also examining the broader role of diet, physical activity, and lifestyle in cancer prevention and survivorship. As plant-based diets gain evidence for their health and sustainability benefits, Rachel looks at their potential role in reducing breast cancer risk.
Breast cancer is the most common cancer in the UK – 1 in 8 women develop the disease at some stage in their lifetime.1 It is estimated that 27% of UK breast cancer cases could be attributed to dietary and lifestyle factors.2 As with all cancers, the risk of developing the disease depends on several factors and varies from person to person.
In recent years it has become clear that an integrated lifestyle pattern of a healthy balanced diet, physical activity and healthy weight has a greater impact on cancer risk than the sum of the individual parts. Research on different dietary patterns and cancer risk is growing, however more is needed before we can make recommendations on which diets offer the best protection against specific cancers.
Could a vegetarian or vegan diet reduce the risk of breast cancer?
A recent study concluded that vegetarians and vegans are less at risk from breast cancer than fish or meat eaters.3
World Cancer Research Fund, Cancer Research UK and Oxford Population Health published results from the new study in which low- and non-meat-eaters had a lower risk of being diagnosed with several types of cancer, including breast cancer, in comparison with regular meat-eaters.
The researchers analysed the diets of more than 450,000 people and categorised them into diet groups depending on their meat intake. Regular meat-eaters were classified as those who consumed processed meat, red meat or poultry more than five times a week; and low meat-eaters less or equal to five times a week. The study also analysed people who didn’t eat meat but did eat fish (pescatarians), and the final vegetarian group included a small number of vegans who never consumed meat, fish, eggs or dairy products.
Overall, they found that compared with regular meat-eaters, the risk of developing any type of cancer was 2% lower in low meat-eaters, 10% lower in fish-eaters, and 14% lower in the vegetarian and vegan group.
Vegetarian and vegan women had a lower risk of post-menopausal breast cancer (18%) in comparison with regular meat-eaters, which appeared to be largely due to the lower body mass index observed in vegetarian and vegan women.
Cody Watling, from Oxford Population Health’s Cancer Epidemiology Unit and lead researcher, said:
“Previous evidence has suggested that vegetarians, vegans and pescatarians may have a lower risk of developing cancer. However, the evidence for a lower risk of developing specific types of cancer has been inconclusive. Being overweight after menopause is known to increase the risk of breast cancer and so the reduced risk of post-menopausal breast cancer in vegetarian and vegan women, due to lower BMI, was unsurprising.
Our group in Oxford is doing further research, funded by World Cancer Research Fund, to assess the risk of cancer across diet groups with larger numbers of vegetarians and pescatarians, as well as looking at vegans separately from vegetarians, to further explore potential explanations for differences in risk of specific types of cancer.”
Dr Giota Mitrou, Director of Research and Innovation at World Cancer Research Fund International, said:
“The results of this study suggest that specific dietary behaviours such as low meat, vegetarian, vegan or pescatarian diets can have an impact on reducing the risk of certain cancers. The findings support our Cancer Prevention Recommendations to limit red and processed meat and increase intake of wholegrains, vegetables, fruit and pulses.”
Diet, lifestyle and breast cancer risk: the strong evidence
World Cancer Research Fund has reviewed the evidence on diet, weight, physical activity and the risk of breast cancer.4 In total, we analysed 119 studies from around the world, comprising more than 12 million women and over 260,000 cases of breast cancer. The findings are separated into pre and postmenopausal breast cancer, as the effects of nutritional factors on breast cancer can depend on menopause status.
Postmenopausal breast cancer
There is strong evidence that:
- being physically active (including recreational physical activity and walking) DECREASES the risk of postmenopausal breast cancer
- breastfeeding DECREASES the risk of breast cancer (menopausal status unspecified) in the mother
- being overweight or obese in young adulthood (between the ages of about 18 and 30 years) DECREASES the risk of postmenopausal breast cancer
- being overweight or obese throughout adulthood INCREASES the risk of postmenopausal breast cancer
- greater weight gain in adulthood INCREASES the risk of postmenopausal breast cancer
- consuming alcoholic drinks INCREASES the risk of postmenopausal breast cancer
Premenopausal breast cancer
There is strong evidence that:
- undertaking vigorous physical activity (such as running, fast cycling and aerobics) DECREASES the risk of premenopausal breast cancer.
- being overweight or obese in young adulthood (between the ages of about 18 and 30 years) DECREASES the risk of premenopausal breast cancer
- being overweight or obese in adulthood before the menopause DECREASES the risk of premenopausal breast cancer
- breastfeeding DECREASES the risk of breast cancer in the mother
- consuming alcoholic drinks INCREASES the risk of premenopausal breast cancer
Practical advice for patients and clients
Based on the strong evidence available we advise women to take the following steps to reduce their risk of breast cancer.
- Don’t drink alcohol
There is strong evidence that drinking alcohol is a cause of breast cancer. We recommend not drinking any alcohol at all. For those who choose to drink, they should follow national guidelines.
- Be a healthy weight
The relationship between weight and breast cancer at different stages of life is complex and more research is needed. Surprisingly, there is evidence that being overweight or obese in young adulthood (between the ages of about 18 and 30) can reduce the risk of pre-menopausal breast cancer. However, being a healthy weight and avoiding weight gain throughout adulthood are important in decreasing your risk of breast cancer after the menopause, which is the most common type of breast cancer, accounting for about 80 per cent of cases. Our recommendation is to maintain a healthy weight throughout all stages of life as being a healthy weight helps to prevent post-menopausal breast cancer and 12 other common cancers, as well as other conditions such as Type 2 diabetes and heart disease.
- Be more active
Vigorous physical activity lowers the risk of premenopausal breast cancer and every type of physical activity (moderate and vigorous) helps protect against postmenopausal breast cancer. We recommend at least 150 minutes of moderate intensity activity or 75 minutes of vigorous activity a week, and to sit less. The more active you are the better.
- If you can, breastfeed your baby
Breastfeeding can help protect mothers against breast cancer. We recommend breastfeeding exclusively for the first six months of life, if able to do so.
What about diet during and beyond breast cancer?
Last month we published a new report summarising the latest research on diet, nutrition, physical activity, and body weight for people living with and beyond breast cancer. The report shows how nutrition, physical activity and body weight affect survival and recurrence and quality of life. For people living with and beyond breast cancer, there is strong evidence that a physically active lifestyle improves health-related quality of life. There was limited evidence of an association that following healthier dietary patterns reduces the risk of all-cause mortality.5
The reports also discuss the limitations of the existing research and make recommendations for future research to strengthen the evidence base. The findings were translated into practical guidance developed with experts including patients and oncologists and oncology dieticians.
Summary of the evidence and guidance
Dietary fibre
There was limited evidence that people who eat more dietary have better health outcomes after a diagnosis of breast cancer. We suggest that people living with breast cancer consider gradually increasing their dietary fibre intake. Foods containing dietary fibre include vegetables, fruits, wholegrains, nuts and seeds.
Soy
There is limited evidence suggesting that people who eat more soy foods have better health outcomes after a diagnosis of breast cancer. There have previously been concerns over soy foods increasing the risk of developing breast cancer, but systematic reviews show no consistent evidence of a link between soy foods and breast cancer risk, or for their harm after a breast cancer diagnosis. The current evidence does not support guidance to consume more soy foods (or to introduce soy foods if these are not currently part of the diet) after a diagnosis of breast cancer, but for those who already consume them, there is no need to stop.
Vitamin D
This review found limited evidence suggesting that those with higher vitamin D status have better health outcomes after a diagnosis of breast cancer, but there was no evidence of any benefit from vitamin D supplements. Therefore, we are not making specific guidance about vitamin D supplements to improve outcomes after a breast cancer diagnosis. People should take any supplements advised by their health care team, but should be cautious of taking over the counter vitamin D supplements if they are already being prescribed vitamin D or calcium supplements.
Body weight
There was strong evidence that those with body weight in the healthy range (measured by BMI, waist circumference and waist-to-hip ratio) after a diagnosis of breast cancer have the best health outcomes. While it is uncertain that deliberate weight loss after a diagnosis by people with overweight or obesity improves these outcomes, we suggest that people who are not underweight aim to avoid gaining weight during and after treatment.
Physical activity
Increasing physical activity improves health-related quality of life after a diagnosis of breast cancer. People who are more physically active have better health outcomes after a diagnosis of breast cancer, but it is uncertain whether increasing physical activity will improve these outcomes. We therefore recommend that people are physically active. However, physical activity should be increased under the supervision of healthcare professionals.
We recommend that individuals living with and beyond cancer speak to their healthcare team before making any changes related to diet, nutrition, physical activity or body weight. Any healthcare professionals using this guidance should consider where a patient is in their cancer journey and interpret the guidance appropriately to suit each person’s individual needs.
As the quality of the evidence-base continues to develop, we hope to expand our guidance to include information for different cancer types.
Take home message
More research is needed to assess the risk of breast cancer across diet groups with larger numbers of vegetarians and pescatarians, as well as looking at vegans separately. In the meantime, we have strong evidence that consuming alcohol and living with overweight or obesity increases the risk of breast cancer. We also have strong evidence that being physically active, and breastfeeding lowers the risk of breast cancer.
There is growing evidence that consuming fibre and soy, being physically active and maintaining a healthy body weight can lead to better health outcomes after a diagnosis of breast cancer. Increasing physical activity also improves health-related quality of life. However, more research is needed before we make specific dietary recommendations for this group.
Useful resources
Diet, nutrition, physical activity and breast cancer report by World Cancer Research Fund and the American Institute for Cancer Research
Diet, nutrition, physical activity and body weight for people living with and beyond breast cancer report by World Cancer Research Fund and the American Institute for Cancer Research
Women’s Health Guide by World Cancer Research Fund
Diet and Breast Cancer by Breast Cancer Now
If you would like to keep up to date with the latest research on lifestyle and cancer, World Cancer Research Fund’s free package for health professionals includes an online cancer prevention course, free resources, and our cancer prevention newsletter.
The Nutrition and Living with Cancer Helpline – we believe everyone who has been diagnosed with cancer should be able to access up-to-date and reliable information about the role of nutrition from diagnosis through to treatment and beyond.
World Cancer Research Fund’s helpline, staffed by Oncology Specialist Dietitians, provides reliable information about the role of nutrition from diagnosis through to treatment and beyond.
Tuesdays: 12pm–2pm Thursdays: 6pm–8pm Call: 0333 034 1988 Email: helpline@wcrf.org
References
World Cancer Research Fund. UK cancer statistics. Published in 2019. Available at: https://www.wcrf-uk.org/preventing-cancer/uk-cancer-statistics/
British Journal of Cancer. The fraction of cancer attributable to modifiable risk factors in England, Wales, Scotland, Northern Ireland, and the United Kingdom in 2015. Published in 2018. Available at: https://www.nature.com/articles/s41416-018-0029-6#Sec9
BMC Medicine. Risk of cancer in regular and low meat-eaters, fish-eaters, and vegetarians: a prospective analysis of UK Biobank participants. 2022. Available at: https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-022-02256-w
World Cancer Research Fund/American Institute for Cancer Research. Diet, nutrition, physical activity and breast cancer. 2018. Available at: https://www.wcrf.org/wp-content/uploads/2021/02/Breast-cancer-report.pdf
World Cancer Research Fund/American Institute for Cancer Research. Diet, nutrition, physical activity and body weight for people living with and beyond breast cancer. 2024. Available at: https://www.wcrf.org/wp-content/uploads/2024/09/CUP-Global-breast-report-0924.pdf
