In recent decades, progress in the early detection and treatment of cancer has led to a dramatic increase in the number of cancer survivors, defined as all people who have been diagnosed with cancer, including before, during and after treatment.
Survival rates vary for different cancers but are highest for colorectal, prostate, melanoma, endometrial and breast cancers. The research focused on aspects of cancer survivorship has grown in parallel to the prevalence of cancer survivors.
There is clear evidence for the role that diet, nutrition and physical activity play in cancer prevention and although survival research is more recent and lesser in volume, there are clear indications that some of these factors are related to outcome.
However, more research is needed to fully understand the impact of interventions that change body composition, dietary intake and levels of physical activity.
Diet, nutrition and physical activity
Historically, dietary advice to cancer patients focused on maintaining a patient’s energy intake and micronutrient sufficiency and on mitigating the effects of nausea and gastrointestinal toxicity.
Prospective research on the role of diet, nutrition and physical activity in people living with and beyond cancer has typically been of short duration, of small size and focused on specific food items or in highly selected populations that do not necessarily represent typical experience. The evidence for the beneficial or adverse effects of specific foods or nutrients is limited.
Diet also plays a role in symptom management. Patients undergoing treatment experience a multitude of symptoms, including fatigue, pain, difficulty breathing, nausea, appetite loss, unintentional weight change and loss of muscle mass.
Physical activity, and specifically various forms of exercise (including cycling, weight training, walking and aerobic exercise), after treatment has been proposed to confer diverse benefits on cancer patients. There is good evidence that these benefits include increased aerobic fitness, reduced fatigue, reduced depressive symptoms, improved quality of life, reduced therapeutic toxicity and improved tolerance.
There is evidence to suggest elevated body fatness is a predictor of poor outcome in breast cancer survivors. The exact cause of this association is unclear. Chronic inflammation associated with obesity may enhance the progression of disease and the impact of overweight and obesity on the risk of other chronic diseases such as diabetes and cardiovascular disease may contribute to reduced overall survival in cancer patients.
In contrast, there is evidence that women who are overweight or obese display adverse tumour characteristics (size, grade) that might affect outcome. It has also been proposed that reduced treatment efficacy might be due to under-dosing of chemotherapy treatment.
Currently it is not possible to conclude with confidence that interventions aimed at reducing body fatness would necessarily improve outcome in breast cancer survivors.
Furthermore, associations have been found between being overweight at diagnosis and longer survival in patients with certain types of cancers, including colorectal and lung. The association between higher body mass index (BMI) and improved outcome is currently unexplained.
Patients who are overweight might have sufficient lean (as well as adipose) tissue to provide resilience against the metabolic side effects of cancer and its treatment. A crucial limitation of the studies reviewing weight is the ability to distinguish between intentional and disease-related (unintentional) weight loss.
While the evidence remains inadequate to make specific Recommendations for cancer survivors with confidence, the Continuous Update Project Expert Panel judges that following the Cancer Prevention Recommendations is unlikely to be harmful to survivors who have completed treatment.
Therefore, cancer survivors are encouraged, if appropriate to their circumstances and unless otherwise advised by a health professional, to follow the general advice for cancer prevention:
- be a healthy weight
- be physically active
- eat more wholegrains, vegetables, fruits and legumes (such as beans)
- avoid sugary drinks and limit consumption of ‘fast foods’ and other processed foods high in fat, starches or sugars
- limit consumption of red meats (such as beef, pork and lamb)
- avoid processed meats and alcohol
- do not rely on supplements