Can Fasting Help Prevent Breast Cancer Recurrence?

Survivors of early stage breast cancer who fasted during sleep for more than 13 hours were less likely to experience a recurrence, according to research from the University of California-San Diego.

Study authors examined the data on more than 2,000 women from 1995 to 2007. All the women had been diagnosed with early stage breast cancer, and their ages at the time of diagnosis ranged from 27 to 70. None of the women in the study had diabetes.

Survivors who fasted for less than 13 hours a night had a 36% higher risk of their cancer returning. The authors, writing in JAMA Oncology, noted that improving blood sugar and sleep might be what made fasting so helpful in reducing risk.

How would blood sugar affect breast cancer prognosis? "Sugar causes spikes in your insulin levels," says Stephanie Bernik, MD, a breast cancer specialist at Lenox Hill Hospital in New York City. "Insulin is the hormone that tells your body to store fat. When you fast, insulin levels are lower, and the body can use fat for energy. Those with leaner body mass have lower estrogen levels [while higher levels of the hormone are associated with an increased risk of breast cancer in postmenopausal women], so it all ties in to breast cancer risk. Therefore, maintaining healthy blood sugar levels is important for overall health."

On the other hand, that doesn't mean that fasting is the key to reduced risk of recurrence: "Fasting may indeed be a marker for decreased cancer risk. But it may not be the act of fasting," Bernik points out. "Perhaps women who fast eat healthier food overall and are more concerned with their overall health."

Except for skin cancer, breast cancer is the most common cancer among U.S. women, according to the American Cancer Society. An estimated 246,660 new cases of invasive breast cancer will be diagnosed in 2016, and the disease will kill 40,450.

Among the risk factors for being diagnosed with breast cancer, according to the National Institutes of Health, are:

  • Alcohol Consumption. The more a woman drinks, the higher her breast cancer risk. For each alcoholic drink consumed per day, the relative risk of breast cancer increases by about seven percent. Women who drink two to three alcoholic drinks per day have a 20% higher risk of breast cancer, according to the Susan G. Komen Foundation.
  • Family History of the Disease. Some breast cancers have genetic components.
  • Excess Weight.. The chances of getting breast cancer are higher in women who are overweight or obese.
  • Lack of Physical Activity. Women who are physically inactive appear to have an increased risk.
  • Long-term Use of Menopausal Hormone Therapy. Using a combination of estrogen and progestin for more than five years appears to increase the risk of developing breast cancer.

To reduce your risk factors, maintain a healthy weight, get regular exercise, and if you drink alcohol, consider cutting back.

And if you only fast between 10 PM and 6 AM the following morning, will that affect your risk? The jury's still out: "More study needs to be done to see if there is a direct link between fasting and breast cancer risk," Bernik says.

Stephanie Bernik, MD, reviewed this article.


Stephanie Bernik, MD. Email interview May 5, 2016.

American Cancer Society. "Cancer Facts & Figures 2016." Atlanta: American Cancer Society; 2016.

Marinac, Catherine R., Nelson, Sandahi H et al. "Prolonged Nightly Fasting and Breast Cancer Prognosis." JAMA Oncology. 31 March 2016.

Brazier, Yvette. "Nightly Fasting May Help Reduce Breast Cancer Risk." Medical News Today. 31 March 2016.

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"What Are the Key Statistics About Breast Cancer?" American Cancer Society. Page last revised May 4, 2016.

"Breast Cancer Statistics." Susan G. Komen. Last updated May 17, 2016.

"U.S. Breast Cancer Statistics." Page last modified May 11, 2016.

"Alcohol." Susan G. Komen. Updated September 29, 2015.

"Table Six: Blood Estrogen Levels and Breast Cancer Risk." Susan G. Komen. Page updated May 8, 2015.