Breast cancer and a high-fiber diet

Imagine if everyone in Chula Vista, Calif., developed breast cancer this year. For perspective, that’s the 15th largest city in California and 75th largest in the United States. … In 2020, an estimated 276,480 new cases of invasive breast cancer are expected to be diagnosed in women – possibly your mom, wife, aunt, sister, or daughter. The number is staggering.

Even more sobering, about 42,170 women are expected to die this year from breast cancer. There is good news: Overall, the breast cancer death rate has decreased by 1.3% per year from 2013 to 2017. The decreases are thought to be, according to the American Cancer Society, the result of treatment advances and earlier detection through screening.

Still, for women in the U.S., breast cancer death rates are higher than those for any other cancer, besides lung cancer.

About 1 in 8 women (about 12%) will develop invasive breast cancer throughout their lifetime. As of January 2020, more than 3.5 million women have a history of breast cancer, including those currently being treated and those who have finished treatment.

(And guys, don’t think it can’t happen to you. The ACS predicts about 2,620 new cases of invasive breast cancer are expected to be diagnosed in men this year. A man’s lifetime risk of breast cancer is about 1 in 883.)

However, despite the facts and figures, research continues to shine a light of hope. Everything from treatments to diet is being studied, and yes – food can make a difference. A recent study that examined dietary fiber intake and breast cancer showed the risk could be reduced by 12%.

So, if you are what you eat, what should that be (hint: bone up on the Mediterranean diet)? We’ll dig into that and also share why cruciferous veggies should become a staple in your everyday meal planning.

As we dive in, remember that less than 15% of women who get breast cancer have a family member diagnosed with it. However, a woman’s risk of breast cancer nearly doubles if she has a first-degree relative (mother, sister, daughter) who has been diagnosed.

Now is the time to begin making a difference in your life. Take the initiative to do something, rather than risk becoming another statistic. Let’s take that first step together …

What the science says

A 1994 case-control study of 451 women in Australia examined the risk of breast cancer to dietary fiber. There were significant reductions in relative risk with increased intake of dietary fiber. The study provided strong support that foods rich in dietary fiber may protect against breast cancer. [1]

In 2016, Dr. Manas Kotepui, Ph.D., reviewed 111 epidemiological studies that focused on nutritional risk factors including dietary fat, meat, fiber, and alcohol, and intake of phytoestrogen, Vitamin D, iron, and folate associated with breast cancer. The evidence suggests that diet may be associated with breast cancer risk depending on the amount and type of foods consumed. Higher intake of foods containing n-3 PUFA, Vitamin D, phytoestrogen, fiber, and folate, together with lower intake of saturated fat, n-6 PUFA, grilled meat, and alcohol, may be beneficial. [2]

With results released in 2016, Harvard research scientist Maryam Farvid examined fiber intake during adolescence and early adulthood to breast cancer risk. 90,534 women completed a dietary questionnaire in 1991; 2,833 invasive breast cancer cases were documented during 20 years of follow-up. The findings support the hypothesis that higher fiber intakes reduce breast cancer risk and suggest that consumption during adolescence and early adulthood may be particularly important. [3]

Another 2016 study, Dietary fiber intake, and risk of breast cancer: A systematic review and meta-analysis of epidemiological studies, examined 24 articles on the relationship between dietary fiber and breast cancer. A total of 51,939 cases and 3,662,421 participants were included. The analysis showed a protective association between dietary fiber intake and breast cancer risk, and the danger could be reduced by 12%. Furthermore, the data showed each 10 g/d increments of dietary fiber intake was associated with a 4% risk reduction. [4]

More recently, dietary guidelines for breast cancer patients have failed to address adequate nutritional intakes of macro- and micronutrients that may improve patients’ nutritional status.

Nutritionist Ana Teresa Limon-Miro led a review of the PubMed and Biomed Central databases across 15 years (2002-17) concerning dietary guidelines for breast cancer patients and the potential impact of a personalized, nutrient-specific diet on patients’ nutritional condition during and after cancer treatment.

The results, taken from five studies covering 2,622 women, indicated breast cancer patients should maintain healthy body weight and lean mass.

Limon-Miro notes that the specifics of nutritional therapy should be based on the patients’ nutritional status, dietary habits, schedule, activities, and cultural preferences for sustained success.

Adequate dietary intakes of food-based macro- and micronutrients rich in β-carotene and Vitamins A, E, and C can both prevent deterioration in breast cancer patients’ nutritional health and improve their overall prognosis. [5]

A review of research published in the October 1996 issue of the Journal of the American Dietetic Association showed that 70% or more of the clinical studies found a link between cruciferous vegetables and protection against cancer. [6]

A 2007 study, however, expressly noted: “evidence of an inverse association between cruciferous vegetable intake and breast or prostate cancer in humans is limited and inconsistent.” [7]

The anticancer role of the Mediterranean diet

Tiffany M. Newman, with Wake Forest University’s Department of Cancer Biology, reported in 2019 that among 2,034 breast cancer patients studied, the Mediterranean diet is considered one of the healthiest of all dietary patterns. Adherence to the Mediterranean diet protects against diabetes, cardiovascular disease, and cancer. A Mediterranean diet was associated with a lower risk for women with all subtypes of breast cancer, and a Western diet pattern was associated with higher risk.

Newman noted epidemiological data supports the impact of dietary patterns on breast cancer risk. Western diet consumption elevates breast cancer risk, while the use of a Mediterranean diet reduces breast cancer risk. She proposed that regulation of the gut and mammary microbiome may be a key influencer on the anticancer role of the Mediterranean diet. Current research detailing the gut microbiome suggests a potential mechanism for dietary influence on cancer risk through inflammation. Restoring balance to the gut microbiome may prove a viable option for the reduction of diet-mediated cancer risks and prognosis factors. [8]

We know that bacteria thrive within us, but did you know bacteria also live in a woman’s breast tissue – the mammary microbiome, mentioned earlier? Researchers believe the microbes may have an effect on breast cancer, according to Gregor Reid, a professor of microbiology and immunology at Western University.

Reid and his team analyzed bacterial DNA found in breast tissue samples from 58 women who were undergoing lumpectomies or mastectomies for either benign or cancerous tumors. They also studied 23 healthy women who had undergone breast reductions or enhancements. The data showed that women with breast cancer had higher levels of some types of bacteria, including Enterobacteriaceae, staphylococcus, and bacillus. Women without cancer had higher levels of other types, such as lactococcus and streptococcus. [9]

In April 2020, a systematic review and meta‐analysis of prospective studies relating to fiber consumption and breast cancer incidence were released by the American Cancer Society. The authors identified 17 cohort studies, 2 nested case-control studies, and 1 clinical trial study. The results showed total fiber consumption was associated with an 8% lower risk of breast cancer.

The researchers, again led by Harvard’s Maryam Farvid, also found that it was only soluble fiber (a substance able to be dissolved, especially in water). Soluble fiber is the most substantial element in foods like beans, lentils, nuts, oatmeal, and peas that had a significant association with reduced breast cancer rates. (Soluble fiber slows digestion and becomes a gel-like substance in the colon.) Future research questions should address the decreased breast cancer incidence as a function of time adhering to a fiber-centric diet.

Insoluble fiber – found in whole grains and cannot be dissolved by the body – also was suggested to reduce the risk of cancer. The effect, however, was not statistically significant. (Both soluble and insoluble fiber are found in varying levels in most foods containing fiber.)

“Our study contributes to the evidence that lifestyle factors, such as modifiable dietary practices, may affect breast cancer risk,” said Dr. Farvid. “Our findings provide research evidence supporting the American Cancer Society dietary guidelines, emphasizing the importance of a diet rich in fiber, including fruits, vegetables, and whole grains.” [10]

Why cruciferous veggies are good for you

What do kale, arugula, and Brussels sprouts have in common? Aside from being the basis for trend-setting vegetable recipes, they’re all delicious cruciferous vegetables and pack a potent 1-2 punch for nutrition and fighting inflammation.

Fun fact: The name “cruciferous” is an informal classification for members of the mustard family and comes from the Latin Cruciferae, meaning “cross-bearing” because the four petals resemble a cross.

Benefits of cruciferous vegetables:

  • Contain Cancer-Fighting Compounds
  • Reduce Inflammation
  • Regulate Blood Sugar
  • Promote Weight Loss
  • Enhance Heart Health
  • Promote Estrogen Balance

While these veggies grow in all different colors, shapes, and sizes, they share several nutritional benefits. Most cruciferous veggies are rich in vitamins and minerals such as folate and Vitamin K. Dark green cruciferous veggies also are an excellent source of Vitamins A and C. They’re also rich in phytonutrients – plant-based compounds that may help to lower inflammation and reduce the risk of developing cancer.

Cruciferous vegetables include:

  • Arugula
  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cauliflower
  • Collard greens
  • Kale
  • Mustard greens
  • Radish
  • Rutabaga
  • Turnip
  • Watercress

Cruciferous vegetables are rich in fiber and low-calorie. Fiber is an essential nutrient to incorporate if weight loss is the goal, as it helps keep you fuller longer.

Cruciferous veggies are also good sources of phytonutrients, which are plant-based compounds that may help lower inflammation and reduce the risk of developing cancer.

In vitro studies have shown sulforaphane, a phytochemical found in cruciferous vegetables, can stimulate enzymes in the body that detoxify carcinogens before they damage cells. [11]

Also present in cruciferous vegetables are glucosinolates. These chemicals are not only responsible for the aroma and flavor of these plants, but they also have been shown to have anticancer effects. According to the National Cancer Institute, studies in rats and mice have demonstrated that indoles and isothiocyanates, the compounds that form from broken down glucosinolates, protect cells from DNA damage, inactivate carcinogens, and have antibacterial and antiviral effects. [12]

The U.S. Department of Agriculture recommends adult women should eat 2.5 cups of vegetables per day; adult men should have 3 cups. One cup of cooked or raw broccoli, Brussels sprouts, or cauliflower counts as 1 cup of vegetables. Two cups of leafy greens, like kale or arugula, count as 1 cup from the vegetable group. [13]

Your total vegetable intake doesn’t have to come from cruciferous vegetables. Still, they should be incorporated daily for maximum health benefits.

The American Cancer Society recommendations for nutrition and physical activity for cancer prevention include:

  • Achieve and maintain a healthy weight throughout life.
  • Adopt a physically active lifestyle.
  • Consume a healthy diet with an emphasis on plant-based foods
  • Limit the amount of processed and red meats:
    • Eat at least 2.5 cups of vegetables and fruits a day.
    • Choose whole grains instead of refined grain products.
    • Drink no more than 1 alcoholic drink per day (women).

Summary of Science

Overall, the connection between reducing the risk of breast cancer and a high-fiber diet is rooted in nutritional research. In 2020, an American Cancer Society review of 20 different studies related to fiber consumption and breast cancer incidence shows total fiber consumption is associated with an 8% lower risk of breast cancer.

A key ingredient to maximizing a healthy diet is cruciferous vegetables, which have nutritional and inflammation-fighting value. These veggies also have phytonutrients and glucosinolates, which have been shown to have anticancer effects.

Cancer Tutor encourages patients to discuss diet and nutritional goals with their doctor and nutritionist. Together you can develop a sustainable plan that will address individual needs for a healthier lifestyle.


  1. High-fiber diets and reduced risk of breast cancer.
  2. Diet and risk of breast cancer.
  3. Dietary Fiber Intake in Young Adults and Breast Cancer Risk.
  4. Dietary fiber intake and risk of breast cancer: A systematic review and meta-analysis of epidemiological studies.
  5. Dietary Guidelines for Breast Cancer Patients: A Critical Review.
  6. Vegetables, Fruit, and Cancer Prevention: A Review.
  7. Cruciferous Vegetables and Human Cancer Risk: Epidemiologic Evidence and Mechanistic Basis.
  8. From the Table to the Tumor: The Role of Mediterranean and Western Dietary Patterns in Shifting Microbial-Mediated Signaling to Impact Breast Cancer Risk.
  9. Microbiota of Human Breast Tissue.
  10. Fiber consumption and breast cancer incidence: A systematic review and meta‐analysis of prospective studies.
  11. Anticancer Activity of Sulforaphane: The Epigenetic Mechanisms and the Nrf2 Signaling Pathway.
  12. Cruciferous Vegetables and Cancer Prevention.
  13. All about the Vegetable Group.

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