There is clear and consistent evidence about the benefits of physical activity for cancer survivors, as acknowledged in recent US and Australian physical activity guidelines for cancer survivors.11,12 However, evidence for weight loss and specific dietary interventions is still an emerging area of research.4 The purpose of this article is to summarise the current evidence and recommendations for providing appropriate body weight and nutrition support for cancer survivors.
Few lifestyle differences exist between individuals diagnosed with cancer and the general population – a population marked by inactivity; overweight and obesity, and suboptimal fruit and vegetable consumption.13,14 Similar to international findings,9 Australian data from the National Health Survey indicated no difference between cancer survivors and those without a cancer history on levels of physical inactivity and fruit or vegetable consumption.15 However, cancer survivors were more likely to be overweight or obese, to have higher levels of alcohol consumption, and to report a range of chronic co-morbid medical conditions.15
Body weight
Obesity has been shown to contribute to the risk of cancer recurrence and survival independent of diet and physical activity.16 Being overweight or obese has been associated with an increased risk of dying of cancer - 14% of cancer deaths in men and 20% in women were attributed to obesity in an American cohort study.17 There was an increased risk of death (30-50%) in heavier women with breast cancer compared to women in the healthy weight range.17 As well, a high body mass index or body fatness before or at the time of a bowel cancer diagnosis appears to be associated with higher all-cause mortality and recurrence.18
Weight gain after a cancer diagnosis has been suggested as a significant contributor to cancer recurrence and decreased survival. In breast cancer patients, weight gain after diagnosis is common in the year following diagnosis.19 In breast cancer patients, for each five kilogram increase in weight, breast cancer mortality increased by 13% and in contrast there was no increase in mortality for women who lost weight.20 Results from the Nurses Health Study indicated a gradient of risk between weight gain and risk of breast cancer recurrence, with the largest weight gains resulting in a 64% increased risk of recurrence.21
The Women’s Intervention Nutrition Study, a randomised control trial of women with early stage breast cancer, highlighted the importance of weight management for cancer survivors. The intervention resulted in significantly lower dietary fat intake among the intervention group, and a corresponding reduction in body weight over five years of follow-up.22 This resulted in a 24% lower risk of recurrence among intervention participants, compared to those in the control group.22 The low fat diet was most beneficial in women with oestrogen or progesterone-receptor negative tumours. Further analysis is required to determine if it was the decrease in fat intake, the change in fatty acid profile, or weight loss that was responsible for the benefits.
Interestingly, another randomised control trial of breast cancer survivors, the Women’s Healthy Eating and Living study, did not show an improvement in survival or breast cancer recurrence.23 Unlike in the Women’s Intervention Nutrition study, the Women’s Healthy Eating and Living study women in both the intervention and control groups experienced small increases in weight, and this may be a factor in the different results.23
In addition to the links between overweight and risk of cancer recurrence and mortality, there is evidence that supports an association between body weight and health-related quality of life, with both body mass index and physical activity contributing independently.24 Healthy weight and overweight cancer survivors reported significantly better physical functioning than those cancer survivors who were obese.24 Lifestyle interventions that prevent weight gain, encourage participation in physical activity, and a healthy diet show some potential to impact on health, survival and quality of life outcomes for cancer survivors.25
Dietary factors
After treatment, some cancer survivors may have residual metabolic and structural damage, exemplified for example by gastrointestinal surgery or xerostomia. These survivors may require individualised medical nutrition therapy with ongoing medical and dietetic support.5
Cancer survivors have reported high levels of interest in dietary interventions and a preference for these interventions to be initiated at diagnosis or soon after.9 A recent review has suggested that changes in health behaviours occurring after the cancer diagnosis may be important determinants in cancer survivors’ wellbeing.26 Although some cancer patients make healthy lifestyle changes after diagnosis, these changes may not be seen in all populations of cancer survivors or, when they do occur, may only be temporary.
There is considerable research on the association between diet and cancer incidence, however there are fewer studies that have looked specifically at cancer survivors.27 Studies of cancer survivors are difficult to compare, as it is such a heterogeneous group with inconsistent definitions for cancer survivors. For example, studies can include one or a number of cancer types and may involve people who have been diagnosed but not yet treated, those with ongoing treatment and those who have been free from disease for years.5 Most studies that have examined diet and cancer survival have been conducted in breast cancer survivors. To date, these studies, as well as those in other types of cancers, have had conflicting results, with some studies indicating a benefit and others suggesting no benefit.27
The results of the two randomised control trials referred to in the body weight section provided conflicting results about the effect of dietary intervention in survivors. The Women’s Intervention Nutrition study found a small improvement in secondary breast cancer events in the intervention arm that followed a reduced fat diet, however this group also lost a significant amount of weight.22 The Women’s Healthy Eating and Living study suggested dietary information for a healthier diet, encouraging five serves of vegetables, two cups of vegetable juice, three serves of fruit, 30g fibre and 20% energy from fat. Yet the study found that dietary intervention made no difference in the incidence of breast cancer recurrence or all-cause mortality. However, both intervention and control arms gained weight in the study.28
The American Cancer Society’s Study of Cancer Survivors-II found an association between meeting fruit and vegetable recommendations and increased health-related quality of life. Breast, prostate, melanoma and bowel cancer survivors who met the recommendations reported significantly higher quality of life than those not meeting fruit and vegetable recommendations.29 While recommendations on diet and cancer survival remain conservative, a healthy diet remains one of the most important lifestyle behaviours for survivors to reduce the risk of other chronic diseases to which survivors are particularly susceptible.6-9,15
Micronutrient supplements
The use of micronutrient supplements is common in cancer survivors. A systematic review of supplement use in cancer patients in the United States reported that an estimated 64–81% of cancer patients and survivors use a vitamin or mineral supplementation, with up to a third of these cancer patients starting micronutrient supplementation after diagnosis.30
Despite the widespread use of supplements in cancer survivors, there are few studies assessing the effect of nutritional supplements on cancer recurrence and survival.5 The World Research Cancer Fund assessed 39 randomised control trials of micronutrient supplementation in cancer survivors including retinol, β-carotene, vitamin B6, multi-vitamins, vitamin E, selenium and isoflavones. It concluded that the evidence “does not show that micronutrients supplements have any benefits in cancer survivors”.5
While not specific to cancer survivors, large-scale randomised control trials on the efficacy of dietary supplements to reduce the risk of cancer have raised serious safety concerns.31 Most water-soluble vitamins are thought to be harmless at pharmacological doses, but there are some concerns about the safety of some nutrients such as selenium, β-carotene, magnesium and chromium which are known to be toxic at pharmacological doses.32
A systematic review of 68 randomised trials of antioxidant supplements in the general population found no significant effect on mortality. When the meta-analysis was restricted to only the high quality trials (47 trials), there was a slightly increased risk of mortality from antioxidant supplements.33 The conclusions drawn were that vitamin C and selenium had no significant effect on mortality and required further study, while treatment with β-carotene, vitamin A, and vitamin E may increase mortality.33
Of particular concern to many breast cancer survivors is soy and phyto-oestrogen. Evidence to date is inconclusive about the role soy foods might play in preventing cancer or cancer recurrence, however high-dose phyto-oestrogen supplementation is not recommended, especially in women with existing breast cancer.34 Soy foods can be encouraged as part of a varied and nutritious diet, consistent with recommendations to consume a diet rich in plant-based foods.
While it appears that people who eat more vegetables and fruit, which are rich sources of antioxidants, may have a lower risk of cancer, the specific components which provide the cancer protective effect are not definitively known.5 As it is not possible to replicate the nutrient combinations found in foods in supplement form, and due to the potential adverse effects high-dose supplementation may have, whole foods appear to be the most beneficial. The World Cancer Research Fund states that dietary supplements are not recommended for cancer prevention and people should aim to meet their nutritional needs through diet alone.5
Some cancer survivors may require micronutrient supplementation due to the late effect of cancer treatment or unrelated co-morbidities. Supplements should only be given when clinically indicated. Instances where lower-dose micro-nutrient supplementation may be indicated for cancer survivors are: biochemically confirmed nutrient deficiency; where dietary approaches have been inadequate; nutrient intakes persistently below recommended intake levels; to meet public health recommended levels of intake if not contraindicated due to cancer therapy; and known health sequelae related to cancer therapy or other co-morbidities such as osteoporosis.31
A daily multivitamin supplement in amounts equivalent to 100% of the recommended dietary intake is a good choice for those cancer survivors who are not able to eat a healthy diet. As high doses of dietary supplements may be associated with toxicity, the use of vitamin and mineral supplements in higher doses should be assessed and discussed on an individual basis.31 Box 2 provides a checklist for cancer health professionals to discuss with survivors who are considering supplementation.