Can an optimal diet or high doses of one particular food help breast cancer patients? Here, we take a look at what influences the outcome after diagnosis.

Body Weight

There is consistent evidence of an association between general overweight and obesity and post-menopausal breast cancer. To add to this, sedentary living is associated with an increased risk for weight gain, overweight and obesity, and subsequently increased cancer risk. Latest research shows that body fatness has contributed to the levels of hormones and growth factors that can promote the growth of cancer cells. As this raises the inflammatory response, increases insulin resistance, and the circulation of estrogen that is associated with cancer promotion and risk, it has been suggested that the prognosis from increased weight on survival after breast cancer is low. Currently, we don’t know if intentional weight loss can reduce these cancer risks.

Dietary fat

One randomised clinical trial (RCT) tested the hypothesis that a low fat diet would increase the relapse-free survival rate. This study determined that this intervention on women with early-stage breast cancer can influence body weight and decrease breast cancer recurrence. In a 5 year follow-up, there was a 24% reduction in recurrence or new contralateral breast cancer. In a 15 year follow-up, overall mortality decreased by 36% in ER negative patients, and 56% in triple negative patients.

Alcohol

There is consistent evidence that consumption of any type of alcoholic drink is associated with cancer. It is suggested that the effect of alcohol on cancer has been attributed to a variety of factors that include:

• The production of carcinogenic substances of alcohol that, once consumed, enhances the penetration of carcinogens into the cells
• Altering chemical compounds, resulting in alterations in regular cell function and activity
• Nutrient deficiencies making tissues susceptible to carcinogenesis.

Though there has been a positive association with breast cancer risk, a causal relationship has not been established, and the factors described above are still speculative.

Fruit and Vegetables

Though very high fruit and vegetable intake may improve overall health, it does not improve the outcome of recurrence or overall survival. This was compared between 5-6 servings per day to 10-12 servings per day.

High and Low-fat Dairy

For recurrence and mortality, studies have found that breast cancer risk increases with high-fat dairy, with survival being halved when consuming low-fat dairy. This is a very general statement, as some studies were not consistent with their classification of dairy foods. Some studies included ice cream and butter, which, according to the Australian Guide to Healthy Eating, are not true representations of dairy products, which are milk, yoghurt and cheese, as they are rich sources of calcium, minerals, protein, and vitamins, including B12. Some other dairy products, such as ice cream, butter and cream can be relatively high in saturated fat and added sugars, so are classified under discretionary choices.

Soy

A versatile bean that is found in foods – soy milk, soy sauce, miso, tempeh, tofu and edamame. In theory, soy may be protective or harmful. Studies have found that soy is associated with a reduced breast cancer risk. However, this association may be modified by menopausal status, BMI, population studied (Asian vs. Western) and age of exposure – childhood, adolescence, and adulthood. There was also a lack of a consistent dose-response relationship between studies. With these factors and conflicting results, there is no definitive conclusion that consuming very little or a lot of soy products will increase or decrease the risk of breast cancer. To date, there is no evidence that soy foods or products cause harm or reduce the effects of chemotherapy, though it may reduce hot flushes and lower cholesterol. Eating soy as part of a healthy balanced diet is safe, but cannot be promoted as protective.

Antioxidants

There is limited data relating to breast cancer. However, an RCT tested the effects of antioxidant supplementation, alongside radiation therapy and three years after, in head and neck cancers. It was found that high doses of Vitamin E and beta carotene reduced the toxic side effects of radiotherapy by a third. The dose involved was 17 times the recommended dietary allowance (RDA) for vitamin E, and 7 times the RDA for beta carotene. These patients were also followed up (6.5 years) and results show that long term supplementation of high doses of antioxidants is associated with adverse effects such as recurrence and increase mortality. Vitamin E, in particular, may displace other antioxidants, which may then increase the risk of free radicals in the body. The results seem beneficial during radiotherapy, but detrimental in the following years.

Other food nutrients

The World Cancer Research Fund (WCRF) supports a Continuous Update Project (CUP) which is an ongoing program that examines studies and literature from around the world. It is reviewed, and reports on each type of cancer are released intermittently. The latest information regarding breast cancer was released in a 2018 report. You can download the full report from the WCRF website.

The future

Ongoing randomized controlled trials (RCTs) are exploring the impact of diet after diagnosis in early-stage breast cancer. Results from some studies may be available in 2022, with others expected by 2024.

In summary, there are no special foods or diets that have been scientifically proven to prevent cancer or improve prognosis. It is just advised that a well-balanced diet of all food groups is followed.

• Keep your weight within the healthy weight range
• Be physically active for at least 30 minutes everyday
• Limit high-calorie foods and avoid sugary drinks
• Eat more vegetables, fruits, wholegrains and legumes
• Limit red meat and avoid processed meats
• Limit alcoholic drinks to 1 standard drink for women, and 2 for men on any given day, with 2 alcohol free days within a week
• Limit consumption of salty food

Written 2017 – last updated December 2023