‘It’s Empowering’: Surgeon Kristi Funk on Diet and Reducing Breast Cancer Risk

By Courtney Davison,

Last Updated:
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Update (9/27/2021) Forks Over Knives hosted Kristi Funk, MD, for a special webinar, “Breast Defense: Cancer-Kicking Strategies,” on Oct. 12, 2021. Watch the replay of Dr. Funk’s live presentation here.

World-renowned breast cancer surgeon Kristi Funk, MD, has worked with celebrity clients and shared her expertise on shows such as Good Morning America and The Dr. Oz Show, and authored the 2018 book Breasts: The Owner’s Manual. For Breast Cancer Awareness Month, Funk has joined forces with the Physicians Committee for Responsible Medicine to launch the Let’s Beat Breast Cancer campaign. We spoke with Funk about the role diet plays in breast cancer, and the four-pronged approach she recommends for radically reducing one’s risk of developing the disease.

How did you come to advocate a plant-based diet for patients?

"I had been your fairly typical physician, in that I never got one second of any nutrition education throughout all of medical school, or during my surgery residency, fellowship, and 20-year-long practice. I definitely was a health-conscious woman, just by my own nature, and I knew some tidbits, so I would throw out some nutritional pearls of wisdom here and there. But when I wrote my book, Breasts: The Owner’s Manual, I wanted to be 100 percent evidence-based in every fact that I mentioned. So when it came to the chapters of the book on what to eat and what not to eat, I truly dove into nutritional science for the first time in my life, really reading studies and understanding. 

"I’d started out researching to prove the way that I had always recommended was correct, which was largely the Mediterranean diet style: lean meat—chicken, turkey, and fish—with lots of fruits and vegetables. I went into the science and was so utterly blown away. ... The cellular response to basically all animal protein and all animal fat is nothing but detrimental to your health." 

Who is at risk for breast cancer and what are the risk factors?

"One in eight women will get a breast cancer diagnosis in her lifetime. Women who are getting older will be at higher risk. The median age for breast cancer in America is 62. So the [peak period] for getting cancer is going to be 52 to 72.

"There's a whole host of different genetic mutations that elevate cancer risk well beyond the one-in-eight population risk. However, one little-known fact, even among some physicians, is that only 5 to 10 percent of all breast cancer on the planet can be attributed to these genetic mutations. … Eighty-seven percent of all women diagnosed with breast cancer don't have a single first-degree relative with breast cancer.

"And it is very true that a family history will potentially significantly elevate your risk … but diet and lifestyle choices are probably intimately associated with family. So even amongst those [who get breast cancer and have] relatives with breast cancer, perhaps it's the modeling of dietary and lifestyle habits within that family structure that elevated the cancer in that family line." 

How do animal products increase breast cancer risk?

"When you eat animal products, estrogen levels skyrocket, and growth factors go through the roof. In particular, the big-daddy bad actor of them all is IGF-1: insulin-like growth factor. 

"IGF-1 screams at all the cells to grow, which is extremely useful, as we all turn over 50 billion cells a day. ... But when you have an excess of IGF-1, your cell turnover is done for the day, but it's still telling cells to grow: to grow atherosclerosis plaque in your arteries; to grow cells that are going to become one to two to four to eight, forming a tumor; and then to grow and metastasize into the liver, into the lungs, into the bones. 

"An excess of IGF-1 only exists as a response to consuming animal protein and animal fat. Otherwise, your brain is super smart. It knows the amount required to tell your liver what to do and doesn't need any extra spurts from the animal protein."

Does eating soy put someone at higher risk for breast cancer?

"This is another area where I dove into the science while writing my book. … I’d been planning to tell people to avoid soy. It turns out that soy is absolutely anti-estrogenic and anti-carcinogenic. 

"I go over the studies briefly in the book, but basically, since 2009, every single study in humans as it pertains to soy shows a dramatic reduction in breast cancer occurrence, breast cancer recurrence, and death. Consuming soy leads to around a 60 percent reduction in getting breast cancer and, for estrogen-driven breast cancer patients, a 60 percent reduction in recurrence risk and 29 percent reduction in mortality. And these are huge studies following thousands of women for years. The largest study to date followed women of different ethnicities for an average of 9.4 years and they found a dramatic decrease from just a half a serving of soy a week. 

"So I encourage women to consume soy, and it doesn't even have to be that much. I advocate for two to three servings daily in all women and especially in breast cancer patients." 

Are there other particular fruits or vegetables that are especially good for lowering breast cancer risk?

"Far and away, No. 1 is cruciferous vegetables and leafy greens.  Cruciferous vegetables are really highly effective in killing breast cancer. 

"Dietary fiber is important, because fiber will bind excess estrogen in your GI tract and make you poop it out. And fiber also improves insulin sensitivity, which ultimately decreases inflammation and boosts your immune system function. It also releases a litany of antioxidant vitamins and anticancer compounds. So, you want to strive to get 30 grams of fiber a day, and studies show a 50 percent drop in breast cancer for those who consume 30 grams of fiber a day. Which, by the way, is only 3 percent of all Americans. 

"Berries not only are a good fiber source but they also have free-radical scavenging power that interferes with cancer cell signaling. ... It actually encourages cancer cells to commit suicide, which we've got a fancier term for in medicine, called apoptosis. And it inhibits angiogenesis, which is the creation of blood vessel conduits [that allows cancer cells to grow]. So, with a cup of berries, you're thwarting the biggest things cancer cells need to thrive."

What are you hoping to achieve with your Let’s Beat Breast Cancer campaign?

"Our goal is to educate physicians and consumers alike about the very practical and actionable steps they can take to dramatically reduce their breast cancer odds. We came up with a four-pronged approach: eat a whole food, plant-based diet; exercise regularly; maintain a [healthy] body weight; and to limit alcohol consumption. By pursuing those four dietary and lifestyle habits, you will absolutely reduce your breast cancer risk by a solid 50 percent, if not more.  

"I think it's extremely exciting and empowering that diet and lifestyle choices [are so important].  … And it's never too late to make healthy dietary and lifestyle changes. Even if you can't be 100 percent committed to say, vegan eating and losing weight and avoiding alcohol, just doing things in part is still a step toward health and away from cancer and illness. And it's a step we can all take."

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About the Author

Courtney Davison

Courtney Davison is Forks Over Knives’ managing editor. A writer and editor on a wide range of subjects, she co-wrote a nationally syndicated advice column from 2016 to 2018 and co-authored the 2018 book Ask Me Anything: A Year of Advice from Dear Annie. She is a longtime vegan and in her free time enjoys trying new recipes and spending quality time with her cats. Find her on LinkedIn.
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