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How a Fiber-Fueled Diet May Help to Reduce Risk of Breast Cancer

Updated: May 30, 2022

Breast cancer is one of the most common cancers among American women. It is estimated by the American Cancer Society that in 2021 alone, around 281,550 new cases of breast cancer will be diagnosed and around 43,600 women will die from breast cancer. That's 43,600 too many. These numbers are profound and illustrate the importance, as a woman, to do everything in your power to mitigate your risks. In addition to getting annual mammograms and doing regular self breast exams, research studies provide convincing evidence that lifestyle factors, such as diet and exercise, can influence breast cancer risk. The American Cancer Society offers dietary guidelines that emphasize the importance of consuming fruits, vegetables, beans, and whole grains to prevent breast cancer. These foods have something in common — fiber.

It may be the fiber in these plants or it may be the more than 25,000 phytonutrients (plant nutrients) that accompany eating whole plant-based foods. There are many proposed mechanisms in which plant-based or plant-centric diets can help to reduce the risk of breast cancer. For today, we'll focus on four proposed mechanisms of how dietary fiber may help to reduce the risk of breast cancer. And, stay tuned as we have two upcoming articles in queue: soy's role in breast cancer prevention and phytonutrients' role in breast cancer prevention.

How does fiber reduce the risk of breast cancer?

Looks, to us, like those cupcakes are made with fiber-filled oat flour!

Improves insulin sensitivity

One proposed mechanism that’s been studied is fiber’s role in improving insulin sensitivity. Insulin sensitivity refers to how sensitive the body's cells are in response to insulin. High insulin sensitivity means that the cells of the body use blood glucose more effectively, reducing blood sugar. Some lifestyle and dietary changes may help improve insulin sensitivity like getting adequate sleep, exercising regularly, and eating a diet high in fiber. Evidence shows that high levels of insulin and insulin-like growth factor 1 (another hormone similar to insulin) play roles as independent breast cancer risk factors. More fiber in the diet equates to increased insulin sensitivity and decreased levels of insulin and insulin-like growth factor, therefore reducing the risk of breast cancer.

Mitigates estrogen dominance

Another mechanism that has been studied is dietary fiber’s role in decreasing the amount of estrogen in blood circulation. Dietary fiber can help to manage excess estrogen by excreting it through digestion, which decreases the plasma concentration of estrogen. Decreased plasma concentration of estrogen has been shown to reduce breast cancer risk. Wondering about where excess estrogen comes from? Diet may play a role. A diet high in saturated fats and processed food, much like the standard American diet, may lead to estrogen dominance. Whole plant-based foods not only have plenty of fiber, but they also have healthier fats that may help to mitigate estrogen dominance.

Helps with weight management

A third proposed mechanism for how fiber reduces breast cancer risk is by helping with weight management. A study done to assess the impact of dietary fiber in participants who were trying to lose weight found that there was a strong association between dietary fiber intake and weight loss in addition to adherence to the dietary program. The participants who increased the fiber in their diet (still within the recommended amount of 25 grams a day) also were most likely to follow other macronutrient guidelines. This is important because obesity is another significant risk factor for breast cancer. In fact, according to the National Cancer Institute, postmenopausal women who are obese have a 20 to 40 percent increase in risk of developing breast cancer compared to women with a healthy weight. Are you convinced about fiber yet?

Fosters a healthy gut

​​A final proposed mechanism for how fiber may reduce breast cancer risk is through the gut microbiome. The gut microbiome of humans includes trillions of microorganisms living inside the body and is associated with overall health and reduction of chronic disease when the microbiome is in balance. Recent studies have highlighted the importance of lifestyle factors in promoting a healthy gut microbiome, namely diet, exercise, and stress management. A plant-based diet that includes a variety of plant-based foods will naturally include plenty of fiber and types of fiber, which can increase the diversity of healthy bacteria in the gut, leading to better health. An increase in the diversity of healthy bacteria may influence breast cancer risk. According to a study done to assess the role of the human gut microbiome in breast cancer, up to 70 percent of breast cancers are fueled by estrogen. Dysbiosis, or a reduction in microbial diversity, may create hormonal imbalance. Consuming a high-fiber diet can diversify healthy bacteria in the gut and, as mentioned previously, increase estrogen elimination. Eliminating excess estrogen robs the cancer cells of a major fuel source. Without a proper fuel source, these cancer cells are decreased, reducing the risk of breast cancer.

One last note: A recent meta-analysis done to assess the results of several previous studies on this topic found a significant association between risk of breast cancer and dietary fiber. The analyses showed that the risk could be reduced by 12 percent and additional increments of 10 grams of fiber per day was associated with a risk reduction of four percent. Another study found that total dietary fiber in adolescence was significantly associated with lower breast cancer risk later in life. Eat your fiber, kids! Fiber-rich foods found to be most effective included whole grains and cereals, vegetables, fruits, legumes, nuts, and seeds (basically, all plants!). The most empowering part of this is that YOU hold the power in controlling your own health!

Are you getting enough fiber?

The odds that you don’t get enough fiber in your diet are, unfortunately, high as less than five percent of Americans get the daily recommended amount of fiber each day. Less than five percent! The daily recommended amount for women is 25 grams a day at a minimum (based on 14 grams per 1000 calories). The caveat is that fiber is only found in plant-based foods so, in order to get more in your diet, adding more plants to your plate is essential.

Here are 5 tips to increase fiber intake:

1. Swap whole grains for processed white carbohydrate foods (whole grain bread,

whole grain pasta, or brown rice for white bread, pasta, or white rice).

2. Add 1-2 Tbsp of chia seeds into smoothies or oatmeal or yogurt bowls (there are 10

grams of fiber in just two tablespoons of chia seeds!).

3. Include veggies at every meal (filling up half your plate is ideal).

4. Snack on nuts and seeds or fruit in place of chips.

5. Try Meatless Monday or one meal a day that is all plant-based (check out Purely

Planted Recipes for plenty of ideas)

For more fiber-filled fun, visit this article on fiber and additional ways to increase dietary intake. For even more inspiration as well as practical tips to increasing fiber intake (including meal plans and recipes!), grab yourself a copy of The Fiber Effect: Stop Counting Calories and Start Counting Fiber for Better Health.

Tip: If you haven’t been eating much fiber and want to start adding more, make sure to increase fiber slowly in order to avoid gastrointestinal discomfort. Also, drink plenty of water as fiber intake increases.

Here’s to spreading the word on fiber during the very important Breast Cancer Awareness Month! Share this blog with all of your gal pals and be sure to comment if you have any questions.

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Hi! My name is Kara and I'm a student in Georgia State University's Coordinated Program for Dietetics. As a former D1 cross country & track athlete, I've seen firsthand the important role that nutrition can play in one's wellbeing. I'm so excited to be pursuing my passion and learning a lot on the way! When I'm not studying or working, you can find me rock climbing with my husband, hanging out with our two dogs, or running on some fun trails.



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