Why Intermittent Fasting is Recommended in Breast Cancer - Lakeside Natural Medicine

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Why Intermittent Fasting is Recommended in Breast Cancer

ByAidanne MacDonald-Milewski, ND February 26, 2021

How does it work?

When you go without eating food for a prolonged period of time, your body ultimately tells you that you’re starving and need to eat something soon. When the body is sent into starvation mode, a stress is put on the cells telling them that they need to kick their survival mechanisms into overdrive. When this happens, cells shift from a state of being well fed so that they can grow to a state or protection and repair. This leads to the body reducing markers of inflammation and oxidative stress as well as better utilizing insulin, glucose and improving lipid profiles.1

See Dr. Axetll’s article on this for more information!

Impact of Insulin in Breast Cancer:

Hormonally responsive breast cancer accounts for at least 78% of breast cancer cases.2 Most tumors of the breast respond and grow when there are elevated estrogen levels in the system, elevated levels of problematic estrogen metabolites (4-OH-estrone & 16-OH-estrone), and poor elimination of this elevated estrogen.

The presence of elevated estrogen or problematic metabolites is often the result of a BRCA1/2 gene or other inherited mutation which alters proper estrogen signaling in the body, but metabolic factors based in the diet can also play a role.

High caloric intake causes an increase in insulin. Almost all cells of the body respond to signals from insulin as sugars are needed for cells to grow. Insulin has been shown to stimulate growth factors that promote the development of new blood vessels (angiogenesis). When an early stage tumor is developing, these newly formed blood vessels help to supply it with the sugars it needs to keep growing.3

In addition to promoting growth factors and inflammation, insulin resistance is also linked with estrogen dominance.  

With this in mind, it is no surprise that post-menopausal obesity is not only a risk factor for the potential development of hormone sensitive breast cancer but also a negative factor in the prognosis or outcome in those who are diagnosed.

See my previous article for more information on insulin and glucose dysregulation!

What does the research say?

Given that intermittent fasting has known benefits for improving insulin sensitivity (among other metabolic parameters), research has looked at the therapeutic potential of fasting in cases of Breast cancer.

A pilot study from 2015 looked at the effects of short term fasting (STF) in conjunction with TAC (docetaxel, adriamycin, and cyclophosphamide) chemotherapy in thirteen patients with stage I, II or III, HER2-negative breast cancer. The intervention group fasted from 24-hours prior to and after treatment, where the control group ate a normal healthy diet. The STF group showed improved insulin regulation, reduced damage to cellular DNA, and IGF-1 levels lower than that of the control group. This study didn’t show a significant benefit in chemotherapy induced side effects with fasting, although that may be due to the short duration of the study.4

A paper from 2016 by Patterson et. al. took data from the Women’s Healthy Eating and Living study on 2413 women with stage I & II breast cancer to identify the effects of nightly fasting on cancer prognosis. Where they found that those who fasted for <13 or >13 hours per night had no differences in all-cause mortality, those who fasted >13-hours nightly were shown to have a lower risk of cancer recurrence at 7-year follow-up.5

Additionally, an animal study published in January of this year showed that time-restricted feeding in an obese, post-menopausal murine model can inhibit mammary tumor growth by improving insulin sensitivity and reducing insulin dependent tumor growth signals.6 Where this information cannot be extrapolated to humans, it provides direction and an exciting prospect for future studies in nutritional interventions for breast cancer prevention in post-menopausal women.

If you’re interested in learning more or how this could be tailored to your lifestyle, be sure to discuss intermittent fasting at your next visit with your Naturopathic doctor.


1.) Longo VD, Mattson MP. Fasting: molecular mechanisms and clinical applications. Cell Metab. 2014;19(2):181-92

2.) Cancer Stat Facts: Female Breast Cancer Subtypes. SEER Database. Accessed from: https://seer.cancer.gov/statfacts/html/breast-subtypes.html. Accessed: February 22nd, 2021.

3.) Yee LD, Mortimer JE, Natarajan R, Dietze EC, Seewaldt VL. Metabolic Health, Insulin, and Breast Cancer: Why Oncologists Should Care About Insulin. Front Endocrinol (Lausanne). 2020;11:58. Published 2020 Feb 20. doi:10.3389/fendo.2020.00058

4.) de Groot S, Vreeswijk MP, Welters MJ, et al. The effects of short-term fasting on tolerance to (neo) adjuvant chemotherapy in HER2-negative breast cancer patients: a randomized pilot study. BMC Cancer. 2015;15:652. Published 2015 Oct 5. doi:10.1186/s12885-015-1663-5

5.) Marinac CR, Nelson SH, Breen CI, et al. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncol. 2016;2(8):1049-55.

6.) Das M, Ellies LG, Kumar D, et al. Time-restricted feeding normalizes hyperinsulinemia to inhibit breast cancer in obese postmenopausal mouse models. Nat Commun. 2021;12(1):565. Published 2021 Jan 25. doi:10.1038/s41467-020-20743-7

Editor’s Note: The information in this article is intended for your educational use only. Always seek the advice of your physician or other qualified health practitioners with any questions you may have regarding a medical condition and before undertaking any diet, supplement, fitness, or other health program.

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