Breast cancer is the most common cancer in Irish, UK and European women, with 367,000 new cancer diagnoses and 91,500 deaths across EU countries in 2012.¹ Incidence rates increase with age, with most breast cancers occurring in women in their 60s and 70s, resulting in high levels of breast cancer associated morbidity and mortality in the elderly. Given the ageing of our European populations and secular trends in reproductive and lifestyle patterns,² breast cancer is likely to become an even more pronounced public health problem in the coming decades. Identifying determinants of breast cancer progression is critical for the development of risk-based management programmes that will be required for affordable and cost-effective control of this disease.

The World Cancer Research Fund (WCRF) published guidelines in 2014 based on global research on how diet, nutrition, physical activity and weight affect breast cancer survivors.³ The report is the most rigorous, systematic, global analysis of the scientific research currently available on breast cancer survivors, and how certain lifestyle factors affect how likely it is that a person will survive after developing the disease. The report specifically focuses on:

• Female breast cancer survivors who are living with a diagnosis of cancer, including those who have recovered from the disease

• The link between diet, weight, physical activity and the likelihood of female breast cancer survivors dying from breast cancer, second primary breast cancer (ie. a new cancer occurring in the same breast after treatment or in the opposite breast), or any other disease.

Obesity and breast cancer

There is consistent evidence of a positive association between greater body fatness and all-cause mortality, breast cancer mortality and development of a second primary breast cancer. 

Compared to normal weight women, obese women have a 75% increased risk of overall mortality. Obesity has been repeatedly shown to be a risk factor for breast cancer recurrence^4,5 and poor survival,^6,7,8 particularly in post-menopausal women. 

A recent review by Azrad and Demark-Wahnefried⁹ summarised data from retrospective studies, secondary analyses from clinical trials and population based studies and concluded that obesity and in some cases being overweight, contribute to negative clinical outcomes in breast cancer patients. Indeed, the association between obesity and breast cancer progression is apparent in several ethnic populations as shown from analyses of the After Breast Cancer Pooling Project clearly demonstrating the scale of this problem globally.⁶

Obesity epidemic

Obesity has become a public health issue of global proportions in recent years. Currently, one-third (33%) of women over 50 years in Ireland¹⁰ are obese and a similar percentage (24%) is found in the UK.¹¹ These rates are among the highest in Europe.¹² Furthermore, there is predicted to be a 33% increase in obesity prevalence over the next 20 years¹³ which in turn is fuelling cancer rates.¹⁴ Therefore, there is an unmet clinical need for appropriate management strategies to be devised for patients with pathologies including cancer that develop in the context of obesity. For example, in the UK currently 53% of breast cancer patients are overweight or obese,¹⁵ while 72% of Irish postmenopausal breast cancer patients are either overweight or obese at the time of diagnosis.¹⁶ There is an urgent need to develop strategies for lifestyle-based management of overweight and obesity in breast cancer patients and to offer guidance at all stages, from diagnosis through treatment and beyond, in terms of weight management for women with breast cancer.

Dietary intake

Dietary patterns: From an epidemiologic perspective, foods and nutrients are never eaten in isolation and their effects are likely to interact. This has led to the adoption of a more holistic approach to identify patterns of dietary intake which represent the complex interaction between foods and nutrients and avoid confounding effects, which may mask true associations between diet and disease. An analysis of dietary patterns in a cohort of 2,522 postmenopausal breast cancer patients in Germany has shown that a prudent dietary pattern (ie. high in vegetables, fruits, vegetable oil, sauces/condiments, and soups/bouillons) before diagnosis decreased risk of overall mortality and recurrence by about 30%. 

Not surprisingly, consumption of the Western/unhealthy pattern (ie. high in red meat, processed meat, and deep-fried foods) resulted in a three-fold increased risk of mortality from causes unrelated to breast cancer.¹⁷

Additionally, the Nurses’ Health Study and Life After Cancer Epidemiology Study in the US have shown similar results when a prudent diet is followed after a diagnosis.^18,19 Practitioners should therefore recommend a prudent dietary pattern to breast cancer survivors encouraging a high vegetable, fruit and fibre intake.

Total fat and Saturated fat: The research group conducted a systematic review and meta-analysis of the evidence to date regarding fat intake and breast cancer survival.²⁰ The association between dietary fat intake (total fat and/or saturated fat) and all-cause, and breast cancer specific survival, has been reported in 15 studies to date and were included in the meta-analyses.

Researchers showed no evidence of an association between total fat intake and risk of breast cancer specific death (Hazard Ratio (HR) = 1.14; 95% confidence interval (CI): 0.86, 1.52) or all cause death (HR = 1.73; 95% CI: 0.82, 3.6). There was, however, evidence of a 50% increased risk of breast cancer death for women in the highest versus lowest category of saturated fat intake. 

Additional research by Hebert et al²¹ has shown that there is a positive association between intakes of butter, margarine, lard, red meat and bacon, foods high in saturated fat, and breast cancer recurrence.  Dietary modification, at the time of diagnosis, to reduce saturated fat intake may therefore be warranted. There are a number of biologically plausible mechanisms whereby saturated fat intake may influence breast cancer progression. It is thought that saturated fat may promote breast cancer growth by increasing low-density lipoprotein and cholesterol levels, by promoting an inflammatory response and by reducing tumour cell death.  

Fibre: The WCRF³ identified three studies that examined the association between fibre intake and all- cause mortality in breast cancer patients. The results showed that fibre intake both before and after a diagnosis of breast cancer was protective against all-cause mortality. For example, all-cause mortality was reduced by 32% for each 10g per day increase in fibre intake before diagnosis; and was reduced by 12% for each 10g per day increase after a diagnosis.³ Breast cancer patients should therefore be advised to meet current dietary recommendations for fibre intake (32g/day).

Other nutrients which are significantly associated with a reduced mortality following a breast cancer diagnosis include folate, vitamin C, and carotenoids.²² These results suggest that in women diagnosed with breast cancer, reduced dietary fat, particularly saturated fat and increased fibre, vegetable, fruit, and other nutrient intakes associated with a plant-based, high-fibre diet improves overall survival after breast cancer diagnosis.²²

Physical activity

Higher recreational physical activity and total physical activity before and after a diagnosis of breast cancer has been shown to decrease risk of death from any cause in breast cancer survivors. For example, a pooled analysis of 22 cohort studies, which included 123,574 women, showed that compared to those who reported low/no lifetime recreational pre-diagnostic physical activity, participants who reported high lifetime pre-diagnostic physical activity levels had a significantly lower risk of all-cause (HR = 0.82, 95% CI 0.70-0.96) and breast cancer-related death (HR = 0.73, 95% CI 0.54-0.98).²³

Similar risk reductions were demonstrated for more recent pre-diagnostic recreational physical activity (HR = 0.52, 95% CI 0.43-0.64), and post-diagnostic physical activity (HR = 0.59, 95% CI 0.45-0.78).  Both pre-diagnostic (lifetime and more recent combined) and post-diagnostic physical activity were also associated with reduced risk of breast cancer events (breast cancer progression, new primaries/recurrence) (HR = 0.72 95% CI 0.56-0.91). Interestingly, the impact of physical activity is greater in breast cancer patients with oestrogen receptor-positive tumours than negative tumours (3). In summary, women with breast cancer should be encouraged to be physically active and meet the recommended guidelines for physical activity ie. 30 minutes of activity (this includes brisk walking) five or more days per week.

Discussions and conclusions

As the number of breast cancer patients in Ireland continues to increase and as survival rates improve, a focus on modifiable lifestyle factors such as diet, body fat and physical activity is essential. 

Breast cancer survivors are at increased risk of developing second primary cancers and other chronic diseases such as cardiovascular disease, osteoporosis and diabetes. Environmental factors such as diet and physical activity are likely contributors to this increased risk and it has been shown that unhealthy behaviours tend to cluster in the population at large and specifically among cancer survivors.²⁴ For example smokers are less likely to be physically active or have a healthy diet. 

There is substantial evidence that healthy lifestyles, including maintenance of a healthy body weight, consumption of a healthy diet, and regular physical activity, have beneficial effects for breast cancer survivors, including prevention or a delay in cancer recurrence, and overall mortality, improvement in co-morbid conditions, quality of life and body composition, and it may also help to alleviate long-term side-effects such as fatigue, anxiety and stress.

Furthermore, a cancer diagnosis is often referred to as a ‘teachable moment’ when patients are motivated to make changes to their lifestyle and practitioners should use this opportunity to provide their patients with guidance in terms of weight management and dietary modification.

References

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