Over the past few decades, many studies have investigated the relationship between single foods and nutrients and breast cancer risk.

The results have strongly suggested that some dietary components (e.g., vegetables, fibre) are protective while others (e.g., red meat, alcohol) can increase the likelihood of developing breast cancer.

These studies, though, don’t consider the combined effects of an overall dietary pattern in which foods, nutrients and other dietary components interact with each other.

While researchers have studied dietary patterns and breast cancer risk, the World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) concluded in their 2018 joint expert report that the evidence for a link between the two was inconclusive.

Meanwhile, research suggests a combination of healthy habits offers even greater protection against breast cancer than isolated healthy lifestyle behaviours.

Now, findings from a comprehensive updated research review add to growing evidence that this is the case, especially for postmenopausal women. Here’s what to know.

The latest research

The updated review was part of the global Continuous Update Project (CUP), an ongoing program that analyzes research on how diet, nutrition and physical activity affect cancer risk.

Evidence from new research is constantly added to CUP. An independent panel of experts then evaluates and interprets it to make judgments and conclusions for cancer prevention.

The new CUP review, which was published online last month in the American Journal of Clinical Nutrition, included 84 studies spanning 22 years, most conducted in North America and Europe.

The researchers evaluated the relationship between breast cancer risk and adherence to a dietary pattern alone or in combination with lifestyle behaviours.

Evidence of breast cancer risk was determined for all females (i.e., studies in which menopausal status was not specified) and also separately for premenopausal and postmenopausal females.

Healthy lifestyle pattern offers greater benefits

Overall, higher adherence to healthy lifestyle patterns that included a healthy diet and other lifestyle factors was consistently associated with lower breast cancer risk and the evidence was graded “strong-probable.”

Findings from studies on dietary patterns only were less consistent and the evidence was deemed limited, meaning it was either suggestive or not conclusive.

Combined dietary and lifestyle patterns were based on advice to maintain a healthy weight, be physically active, follow a healthy diet and consume moderate-to-zero alcohol.

Lifestyle patterns specific for cancer prevention (e.g., WCRF/AICR and American Cancer Society lifestyle scores) included certain dietary components linked to a lower cancer risk.

Only higher adherence to the WCRF/AICR and American Cancer Society lifestyle patterns, however, was consistently tied to lower breast cancer risk in all and in postmenopausal females; the evidence was graded “strong-probable.”

Fewer studies on lifestyle patterns and breast cancer risk in premenopausal females were available; the evidence was graded limited, but suggestive.

How diet can help guard against breast cancer

Healthy dietary patterns are thought to lower inflammation and oxidative stress in the body, factors thought to play a role in the initiation and progression of breast cancer.

Adhering to a healthy dietary pattern may also help control insulin and insulin-like growth factors, hormones implicated in breast cancer risk.

What’s in (and not in) a cancer-prevention dietary pattern

An eating pattern tied to a lower overall cancer risk is focused on plant foods – vegetables, fruit, whole grains (at least half your daily grains), beans (including soybeans) and lentils.

When it comes to vegetables and fruit, the American Cancer Society advises eating 2.5 to 3 cups of vegetables and 1.5 to 2 cups of fruit each day. That’s similar to the Canadian Cancer Society’s recommendation to fill half your plate with vegetables and fruit for each meal.

Variety is important too.

To consume a wide range of nutrients and protective phytochemicals, include dark green (e.g., spinach, rapini, arugula), orange (e.g., carrots, sweet potato, winter squash), cruciferous (e.g., broccoli, cauliflower, Brussels sprouts) and allium (e.g., garlic, onions) vegetables. Vary the types of fruit in your daily diet.

A diet rich in plant foods is also high in fibre. The WCRF and AICR recommend consuming at least 30 g of fibre each day from whole foods.

Red meat is limited to three servings a week (12 to 18 ounces in total). Processed meat should be eaten sparingly, if at all.

Ultra-processed foods (e.g., fast foods, commercial baked goods, ready-to-eat or ready-to heat foods) are to be limited. Sugar-sweetened drinks should be avoided.

For cancer prevention, it’s best not to drink alcohol. If you choose to drink, the Canadian Cancer Society advise no more than two standard drinks per week (one standard drink is 5 ounces of wine, 1.5 ounces of 40-per-cent spirits or 12 ounces of 5-per-cent beer).

Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD