Sage Advice Blog

Prolonged Nightly Fasting and Breast Cancer

January 17, 2019

Alex Speers ND, MS


In the past few years, fasting has gained a considerable amount of interest among patients with cancer. Pre-clinical data and some early human data have suggested that fasting around chemotherapy may reduce the incidence and severity of treatment-related side effects and currently, there are several clinical trials being conducted to investigate this question. While the combination of fasting with conventional treatments is an intriguing idea and has received the greatest amount of attention, there is also the question of whether fasting after conventional treatments could have any benefits for patients with cancer.


That was the question for the authors of a study published in JAMA Oncology called “Prolonged Nightly Fasting and Breast Cancer Prognosis.” In this study, researchers sought to investigate whether the duration of nightly fasting (the period of time between a person’s last meal at night and their first meal the next morning) could predict recurrence among breast cancer survivors.


The data came from the Women’s Healthy Eating and Living study, a study which followed 2,413 women with breast cancer from 1995 to 2007, who were aged 27 to 70 years old at diagnosis. Each woman in the study filled out a 24-hour dietary recall at baseline, 1 year, and at year 4. Based on these questionnaires, the researchers were able to estimate how long patients fasted each night.


For the cohort of 2,413 women, the mean (or average) nightly fasting duration was 12.5 hours per night. In other words, the average woman in the study stopped eating each night at, let’s say, 8:00PM, and didn’t eat again until 8:30AM. What researchers found was that women who fasted less than 13 hours each night had a 36% increased risk of breast cancer recurrence compared to women who fasted 13 hours or more. Fasting less than 13 hours each night was not, however, associated with an increased risk of death, either from breast cancer or any other cause.


The results of this study suggest that there may be a benefit in prolonging the duration of nightly fasting for women with a history of breast cancer, as it may be associated with a decreased risk of recurrence. It’s important to remember that this is an observational study, which means that we can only say that a shorter duration of nightly fasting is associated with an increased risk for breast cancer recurrence. We don’t know that it is the direct cause of the increased risk. It’s possible (and likely) there are other factors involved and that nightly fasting shouldn’t be our only focus. In addition, it’s possible that patients did not have a perfect memory when it came to completing their 24-hour dietary recall questionnaires, which may have influenced the results. That said, thirteen hours of fasting each night (ex: 7:30PM to 8:30AM or 8:30PM to 9:30AM) is likely an achievable goal for most patients and offers a non-drug strategy to potentially reduce the risk of breast cancer recurrence.


Marinac CR, Nelson SH, Breen CI, et al. Prolonged nightly fasting and breast cancer prognosis. JAMA Oncol. 2016;2(8):1049-1055.


DISCLAIMER: These statements have not been evaluated by the Food and Drug Administration. There are no financial ties to any supplement companies, pharmaceutical companies, or to any of the products mentioned in this post. This post is not meant to treat, cure, prevent, or diagnose conditions or diseases and is meant for educational purposes. As always, please consult your doctor before trying any new treatments or supplements.


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