How fiber-rich foods protect against breast cancer

January 02, 2018 by Joel Fuhrman, MD

Health Concerns: Cancer, Breast Cancer

Breast cancer-  two words that strike fear in every woman.  The good news is women can help lessen their risk.  One important defense is to consume a high fiber diet.

A 2011 meta-analysis of 10 scientific studies found that higher fiber intake is associated with lower risk of breast cancer.1 In 2012, another meta-analysis of 16 studies came to the same conclusion.2 In the Nurses’ Health Study, higher fiber intake during childhood and adolescence was linked to a decrease in the risk of breast cancer in adulthood.3

How fiber impacts breast cancer risk

Given that animal products, refined grains, sugars and oils contain little or no fiber, fiber intake is a marker for greater intake of natural plant foods, many of which are known to have a variety of anti-cancer phytochemicals. Some breast cancer protective substances that have already been discovered include isothiocyanates from cruciferous vegetables4, organosulfur compounds from onions and garlic,5 aromatase inhibitors from mushrooms,6 flavonoids from berries,7, 8 lignans from flax, chia and sesame seeds,9 and inositol pentakisphosphate (an angiogenesis inhibitor) from beans.10  

Influence of fiber, glucose, insulin on breast cancer

High-fiber foods help to slow emptying of the stomach and absorption of sugars, which decreases the after-meal elevation in glucose. This is meaningful because elevated glucose levels lead to elevated insulin levels, which can send pro-cancer growth signals throughout the body, for example via insulin-like growth factor 1 (IGF-1).11 As such, high dietary glycemic index and glycemic load (characteristic of refined grains and processed foods) are associated with an increase in breast cancer risk.12-14  Accordingly, a study on Korean women found that higher white rice intake was associated with higher breast cancer risk.15

Fiber, estrogen, and breast cancer

Increased exposure to estrogen is known to increase breast cancer risk.16-18 A woman may be exposed to estrogen via her ovaries’ own production, estrogen production by excess fat tissue, or environmental sources such as endocrine-disrupting chemicals (like BPA, a chemical added to many consumer products). Fiber can reduce circulating estrogen levels, thereby reducing breast cancer risk, because it helps to remove excess estrogen from the body via the digestive tract. Fiber binds up estrogen in the digestive tract, accelerates its removal, and prevents it from being reabsorbed into the body.19-21

In addition, soluble fiber (as shown in studies using prunes and flaxseed) seems to alter estrogen metabolism so that a less dangerous form of estrogen is produced, whereas insoluble fiber (wheat bran) did not have the same effect. 22, 23  For this reason, beans, oats, chia seeds and flaxseeds may provide some extra protection due to their high soluble fiber content.

Foods rich in fiber

Although most people probably just associate whole grains with fiber,  beans contain more fiber than whole grains, and vegetables and fruits (and some seeds) contain comparable amounts – here are a few examples:

1 cup cooked quinoa – 5 grams fiber

1 cup cooked brown rice – 4 grams fiber

1 cup cooked kidney beans – 11 grams fiber

1 cup cooked broccoli – 6 grams fiber

1 cup blueberries – 4 grams fiber

1 tablespoon chia seeds – 6 grams fiber

Overall benefits of fiber: promotes weight loss and digestive health

Fiber, by definition, is resistant to digestion in the human small intestine. This means that during the digestive process, fiber arrives at the large intestine still intact. Fiber takes up space in the stomach but does not provide absorbable calories, and it also slows the emptying of the stomach.24 These properties of fiber make meals more satiating, slow the rise in blood glucose after eating and promote weight loss. In the colon, fiber adds bulk and accelerates movement, factors that are beneficial for colon health. Soluble fiber (primarily from legumes and oats) is effective at removing cholesterol via the digestive tract, resulting in lower blood cholesterol levels. Some types of fiber are fermented by intestinal bacteria. The fermentation products, short-chain fatty acids (SCFA) such as butyrate and propionate, have anti-cancer effects in the colon and also serve as energy sources for colonic cells. These SCFA are also thought to contribute to promoting insulin sensitivity and a healthy weight.25, 26

Fermentable fiber also acts as a prebiotic in the colon, promoting the growth of beneficial bacteria. Fiber intake is associated with a multitude of health benefits, including healthy blood pressure levels and reduced risk of diabetes, heart disease and some cancers.24, 27

Importance of choosing high-fiber and high-nutrient foods

Yes, fiber itself has some breast cancer-protective properties, like limiting glycemic effects of foods and assisting in estrogen removal, but we get optimal protection when we focus on foods that are both rich in fiber and rich in micronutrients and phytochemicals. 

G-BOMBS contain fiber along with numerous anti-cancer phytochemicals, however, green (cruciferous) vegetables, mushrooms, flax and chia seeds in particular contain anti-estrogenic substances in addition to fiber, making them more effective breast cancer fighters than whole grains. Remember, beans are higher in fiber (and resistant starch) and lower in glycemic load than whole grains, making beans a better carbohydrate choice.

A Nutritarian diet is designed to include a full portfolio of the most protective foods to prevent cancer and slow the aging process.  Advances in nutritional science make winning the war against cancer a reality in our lifetime. 

Learn how nutritional excellence can normalize unfavorable hormone levels and harness the body's ability to fight cancer, especially of the breast and prostate. Watch my video-on-demand lecture, How to Prevent Breast Cancer.

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Joel Fuhrman, M.D. is a board-certified family physician, six-time New York Times bestselling author and internationally recognized expert on nutrition and natural healing, who specializes in preventing and reversing disease through nutritional methods. Dr. Fuhrman coined the term “Nutritarian” to describe his longevity-promoting, nutrient dense, plant-rich eating style.
For over 25 years, Dr. Fuhrman has shown that it is possible to achieve sustainable weight loss and reverse heart disease, diabetes and many other illnesses using smart nutrition. In his medical practice, and through his books and PBS television specials, he continues to bring this life-saving message to hundreds of thousands of people around the world.