Nutrition strategies for preventing breast cancer

October 1, 2002 in Cancer Prevention, Healthy Eating, Women's Health

Nutrition strategies for preventing breast cancer

Breast cancer is the most common type of cancer among Canadian women. Sadly, fifteen Canadian women die every day from breast cancer. But the good news is that the death rate from breast cancer has decreased by 10 percent over the past 15 years. This is largely due to the fact that more and more women are having mammograms allowing for earlier detection.

Simply put, cancer is a disease in which abnormal cells grow out of control. When enough of these cells accumulate, a tumor forms. Finally, if the cancer cells are able to break away from the tumor, they can circulate through the body and take up residence in another organ, a process called metastasis. Every cell has a genetic blueprint, called DNA (deoxyribonucleic acid). The DNA of cells contains genes that program cell reproduction, growth and repair of all body processes. Sometimes genes can become damaged by a mutation that occurs during normal cell division or by exposure to cancer causing agents (carcinogens). Such damage can result in cancer. Flawed genes can be inherited from your parents. However, very few cancers are the result of inherited genes.

Cancer is not explained by genetics alone. Experts agree that cancer is the result of an interaction between genes and environmental factors. For instance, you might have a mutated gene that predisposes you to breast cancer, but because you eat a low fat diet with plenty of fruits and vegetables, the cancer may never express itself.


Who’s at risk?

The clearest risk factors for breast cancer are associated with hormonal and reproductive factors. It is thought that estrogen promotes the growth and development of mutated breast cells. It seems that the longer breast tissue is exposed to the body's circulating estrogen, the greater the risk for breast cancer.


  • Age. Breast cancer is more common in women over 50 years of age.
  • Previous breast cancer. A history of breast cancer increases the odds that a woman will get breast cancer again, in the same and the opposite breast.
  • Family history of breast cancer. If you have a first degree relative with breast cancer (a mother or a sister) your risk is approximately doubled but there is a greater risk if more than one close relative is affected, or if the cancer has occurred at a young age in family member.
  • Age of first pregnancy. Women who have children before 30 years of age have a lower risk of breast cancer. Women who have their first child after 30 have a higher risk and women who never have children are at an even greater risk.
  • Age of first period (menarche). Onset of your period before 12 years of age is associated with a slightly higher risk of breast cancer.
  • Late menopause. Women who menstruate for longer than 40 years have a slightly higher risk of breast cancer.


Preventing breast cancer with diet

Dietary factors such as fat, alcohol, fibre, fruits and vegetables have all been well studied. Below I list nutrition recommendations based on the current body of scientific evidence. Some of these strategies have strong research to support their adoption; others have evidence to suggest that they may be helpful.

Eat less fat. It is believed that dietary fat may increase breast cancer risk by effecting estrogen metabolism. Studies have found that vegetarian women who follow a low fat, high fibre diet have lower levels of estrogen and less breast cancer. A high fat diet may also lead to breast cancer by promoting weight gain and body fat accumulation, which in turn increases the risk of breast cancer.

A large Canadian study is underway to determine if a very low fat diet can prevent breast cancer. So far one report from this trial found that women who ate a 21 percent fat diet for two years had significantly reduced dense breast areas seen by mammogram (dense breast areas are a risk factor for cancer), compared to women on a 30 percent fat diet. Another report from this research group revealed that women who followed a 15% fat diet for two years had lower levels of circulating estrogen, which could offer protection over the long term.

Eat less meat. Some studies show that higher meat intakes are linked with a greater risk of breast cancer. The harmful effect of meat may be due to its saturated fat content, or it may be due to the way it's prepared. Cooking meat at high temperatures forms compounds called heterocyclic amines, which have been shown to cause breast tumors in animals.

This may hold true for women too. A University of Minnesota study found that women who ate hamburger, steak and bacon well done were more than four times as likely to have breast cancer than women who enjoyed their meat rare or medium done. Until we know more about the effect of cooked meat, breast cancer experts advise that we consume no more than 3 ounces (90 grams) of meat each day.

Eat more fish. Studies show that consuming plenty of fish for many years is associated with a lower risk of breast cancer. While no trials have been done in women, one animal study did find that omega-3 fats from fish oil actually suppressed human breast cancer cell growth and metastases in female mice (scientists will inject human breast cancer cells into mice to study the effects of different carcinogens). Despite the lack of strong evidence for fish's protective effect, the existing studies do suggest that you get more omega-3 fats in your diet. Aim to eat fish three times a week.

Eat more soy foods. Populations who consume the largest amount of soy in their diet have the lowest rates of breast cancer. Researcher attribute soy's possible protective effect to naturally occurring compounds called isoflavones. Once in the body, isoflavones behave like weak estrogen compounds and are able to attach to estrogen receptors in the breast. In so doing, they can block the ability of a woman's own estrogen from taking that spot. That means that breast cells have less contact with estrogen.

So far no study has been conducted to show what years of eating a high soy diet does to breast cancer risk. A handful of studies have shown that a regular intake of soy isoflavones may lower circulating levels of estrogen and this might reduce a woman's future risk of breast cancer. Other studies show that consuming a soy-rich diet can lengthen a woman's menstrual cycle, thereby influencing how much estrogen your breast cells are exposed to. Based on what we know today, most experts believe women must consume soy foods over their lifetime to realize the potential benefits of soy isoflavones on breast health.

The estrogen-like properties of isoflavones have led some experts to be concerned about the use of soy in women with breast cancer because estrogen may increase this risk. Some preliminary studies show that soy has protective effects for breast cancer while others suggest soy might increase breast cell growth.

Because we lack sufficient reliable information about the effect of soy foods in women with breast cancer, a history of breast cancer, or a family history of breast cancer, the use of soy should be treated with caution. Until more is known, avoid consuming large amounts of soy each day. Avoid using soy protein powders and isoflavone supplements. Consuming soy foods three times a week as part of a plant based diet is considered safe.

Use ground flaxseed. These tiny whole grain brown and golden seeds contain natural plant estrogens called lignans. Once in the body, phytoestrogens from flaxseed have a weak estrogen action and they are able to bind to estrogen receptors (just like soy isoflavones). In so doing, they appear to block the action of our body's own estrogen on breast cells. Animal studies conducted at the University of Toronto found that have shown that flaxseed has anti-cancer properties. And a recent Canadian study suggests that 50 grams (about two tablespoons) of ground flaxseed can slow breast cancer growth in women.

Aim to get one to two tablespoons of ground flaxseed each day. Grind your flaxseed in a clean coffee bean grinder or use a mortle and pestle. You can also buy flaxseed pre-ground at health food stores. Once you grind flaxseed, store it in an airtight container in the fridge or freezer. The natural fats in flaxseed go rancid quickly if exposed to air and heat. For tips on adding flaxseed to your foods, refer to page 70, Chapter 5 Elements of a Healthy Diet.

Eat plenty of fruits and vegetables. Over 200 studies from around the world have shown that a diet high in fruit and vegetables lowers the risk of many cancers, including breast cancer. Researchers from Harvard University studied more than 89,000 women and found that those who ate more than 2.2 servings of vegetables a day had a 20 percent lower risk of breast cancer compared to those who ate less than one serving. Another study in premenopausal women found that high total vegetable intake lowered the risk of breast cancer by 54 percent.

It appears that dark green vegetables are most protective. Spinach, kale, rapini, collard greens, Swiss chard and Romaine lettuce are good sources of beta-carotene, an antioxidant nutrient that might protect breast cells from damage caused by harmful free radical molecules.

Increase your fibre intake. Evidence suggests that a high fibre diet may offer protection from breast cancer. Toronto researchers found that 20 grams of fibre per day was associated with lower risk. Fibre may help lower the risk of breast cancer by binding to estrogen in the intestine and causing it to be excreted in the stool. Everyday our intestine reabsorbs estrogen from bile, the compound that's released into your intestine from your gallbladder to help digest fat. If dietary fibre can attach to this estrogen and facilitate its removal from the body, your body has to take estrogen out of your bloodstream to make more bile. The net result - a lower level of circulating estrogen. It's possible that following a high fibre diet for many years that could lower your risk for breast cancer.

The studies suggest that dietary fibre works best if you follow a low fat diet. So adding a little wheat bran to a diet that's high in fat and low in fruits and vegetables probably won't do you much good. Foods like wheat bran, whole grains, and some vegetables contain mainly insoluble fibres. It's wheat bran that's been studied the most in relation to breast cancer risk. To boost your intake of insoluble fibre and wheat bran, try the following:

  • Strive for at least 5 servings of fruits and vegetables every day.
  • Leave the peel on fruits and vegetables whenever possible.
  • Eat at least 5 servings of whole grain foods each day.
  • Buy a high fibre breakfast cereal. Add one-half to one cup of 100% bran cereal to your morning meal.
  • Add two tablespoons (25 ml) of natural wheat bran or oat bran to cereals, yogurt, casseroles and soup.
  • Add nuts and seeds to salads.
  • Reach for high fibre snacks like popcorn, nuts, dried apricots or dates.

To avoid intestinal distress, gradually build up your fibre intake. Be sure to drink eight ounces of fluid with every high fibre meal and snack. 

Avoid alcoholic beverages. In a review of 38 studies conducted up until 1992, researchers concluded that having one, two or three drinks a day all increased the risk of breast cancer. The more alcohol a woman consumed, the higher her risk. Alcohol may make breast cells more vulnerable to the effects of carcinogens or it may enhance the liver's processing of these substances. Alcohol may also inhibit the ability of cells to repair faulty genes. Alcohol may also increase estrogen levels in the body.

Nutrition and cancer experts recommend that women do not drink alcohol. If consumed at all, alcoholic drinks should be limited to one a day or seven per week.

Manage your weight. Gaining weight after menopause is linked with a higher risk of breast cancer. Obesity may influence breast cancer risk by increasing circulating estrogen levels since estrogen is produced in body fat cells. If you are overweight, or you have gained some weight since menopause, I strongly advise that you take steps to lose weight. Start by determining your body mass index to get a sense of how your current weight is affecting your health.

Fill up on folate. If you do drink some alcohol make sure to meet your daily requirements for this B vitamin. A Harvard study found that among women who consumed 15 grams of alcohol per day (about a glass and a half of beer or wine), those with the highest daily intake of folate (600 micrograms/day) had a 45 percent lower risk for breast cancer compared with women with the lowest folate intake (150-299 micrograms/day). It's thought that alcohol interferes with the transport and metabolism of folate, and may deprive body tissues of this B vitamin, which is essential to DNA synthesis.

The best food sources of folate include spinach, lentils, orange juice, asparagus, artichokes, and while grain breads and cereals. To supplement take a multivitamin and mineral or a B complex supplement. If you take separate folic acid supplements, buy one that has vitamin B12 added (folic acid is the synthetic form of folate found in vitamin pills and fortified foods; folate refers to the vitamin as it occurs naturally in foods).


Recommended Websites:

Canadian Cancer Society

A service provided by:National Cancer Institute (

A service provided by:
Sunnybrook and Women's College Health Sciences Centre and
The Centre for Research in Women's Health


The above excerpt is from "Leslie Beck's Nutrition Encyclopedia" (Penguin Canada, 2001/2003), available at bookstores across the country. The following is copyrighted and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or means - electronic, mechanical, photocopying, or likewise.


All research on this web site is the property of Leslie Beck Nutrition Consulting Inc. and is protected by copyright. Keep in mind that research on these matters continues daily and is subject to change. The information presented is not intended as a substitute for medical treatment. It is intended to provide ongoing support of your healthy lifestyle practices.