The role of diet in breast cancer
Breast cancer has been at the scientists’ centre of attention for many decades. It’s not only one of the most frequent types of cancer but it can be hormone sensitive which makes the treatment more difficult. Diet has been linked not only to the prevention and treatment of breast cancer but also to natural regulation of hormone levels. In the case of breast cancer, diet is of high importance both because of nutrient content and due to its effect on body weight. Being overweight is one of the risk factors for breast cancer.
What does the science say?
During the Shanghai Breast Cancer Study (Cui et al., 2007), a wealth of data from breast cancer patients and healthy women of similar age was collected and the risk of breast cancer in relation to diet evaluated. The authors noticed there were two dietary patterns – ‘vegetable-soya’, characterised by fruit and vegetables, pulses and grains; and ‘meat-sweets’ characterised by meat, fatty foods and sweets. The analyses of the data revealed that the ‘meat-sweet’ pattern was significantly associated with increased risk of estrogen receptor-positive breast cancer among postmenopausal women and this association was even stronger if the women were overweight.
Another large study was conducted in Singapore where 34,000 women’s dietary patterns and health were followed for the average period of ten years (Butler et al., 2010). Similar to the study above, the researchers identified two dietary patterns, ‘meat-dim sum’ and ‘ vegetable-fruit-soya’. And the results revealed a direct relationship between diet and breast cancer risk in postmenopausal women - the greater the intake of the foods from the vegetable-fruit-soya category, the lower the risk of breast cancer. More specifically, the risk was 30 per cent lower in women who had the highest intake of these foods.
And when a long-term study followed women’s health and diets in Italy, it arrived at a comparable conclusion (Sieri et al., 2004). Women with mostly plant-based diets high in raw vegetables had up to 36 per cent lower risk of cancer than women who ate more animal-based and processed foods. The risk reduction was even higher for women who maintained a healthy weight.
Brennan et al. (2010) reviewed a myriad of studies on dietary patterns and breast cancer risk and reached a foreseeable conclusion - women consuming a diet high in plant-based foods, healthy fats and low in alcohol have a lower risk of breast cancer than women eating typical Western diets high in meat and animal fats.
As a part of the enormous Nurses’ Health Study, a Harvard scientific team investigated whether there is any link between the risk of breast cancer and dietary protein source (Farvid et al., 2014). During the 20 years of follow-up, it emerged that higher intake of red meat was associated with an increased risk of breast cancer. When the effects of different protein sources were estimated based on the dietary data, the scientists arrived at the conclusion that substituting one serving a day of red meat for one serving of pulses would mean a 15 per cent lower risk of breast cancer among all women and 19 per cent lower risk among premenopausal women.
Ferrari et al. (2013) focused on a different dietary component in their analysis of the EPIC (European Prospective Investigation into Cancer and Nutrition) study data. They investigated the relation between dietary fibre, its main food sources and breast cancer risk. The data showed that higher intake of fibre lowers the risk of breast cancer and the association was particularly strong with fibre from vegetables. This risk reduction was independent of the women’s menopausal status or cancer hormone sensitivity. The UK Women’s Cohort Study brought similar results - an increased fibre intake was linked to a lower breast cancer risk among British women (Cade et al., 2007).
To assess the influence of a radical diet change and exercise on women at risk of breast cancer, Barnard et al. (2006) enlisted volunteers on a two week program. The women, who were all postmenopausal and overweight, agreed to follow a very low-fat, high-fibre diet consisting mainly of fruits, vegetables and wholegrains with very limited amounts of animal protein and daily aerobic exercise. At the end of the two-week period, their hormone levels decreased, including IGF-1 which dropped by as much as 19 per cent. The women also lost weight which is an important factor in breast cancer prevention and their blood sugar control improved. The serum isolated from the participants’ blood samples before and at the end of the trial was used on breast cancer cells in a cell culture to see if there would be any difference in the cell growth. The results were of major importance as the after the intervention, the cancer cell growth was significantly slowed down and considerably more cancer cells died compared to pre-intervention.
Probably the best known case study of diet change and breast cancer is Professor Jane Plant who had conducted extensive research on diet and breast cancer to treat her own condition. What she found out and the hundreds of studies she based her decisions on led her to a conclusion that a vegan diet is necessary for successful breast cancer treatment (Plant, 2007). Her advice has since helped thousands of women and has been supported by many experts.
For references and more information, see The Incredible Vegan Health report. For practical guidance on how to improve your diet in order to help prevent or recover from breast cancer see Viva! Health's breast cancer resources.