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Can Intermittent Fasting Prevent Breast Cancer ?

Intermittent fasting can lower risk factors of breast cancer. Learn more about how intermittent fasting can help to prevent breast cancer.
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Intermittent fasting is highly beneficial for women's health. One of the reasons is intermittent fasting can lower risk factors for breast cancer.

Written by
Vera Bokor
Health and Wellbeing Coach

Breast cancer became a common disease among young women. It is not a menopausal problem anymore (1). Lifestyle and diet play a big role in developing this disease. Even though intermittent fasting is not a diet, but an eating pattern, it can decrease the risk of developing breast cancer (2).

“Cancer is a seed that flourishes in the right soil, under the right conditions”- Jason Fung, M.D. (3)

What dietary factors are responsible for breast cancer?

Cancer is a very complicated disease, but it is known as a disease of excessive cell growth. Every time we are talking about growth, insulin is involved. Excessive insulin leads to metabolism disorders. Cancer is caused by mutations in the DNA of our cells, but metabolic dysfunction is a strong driver of the disease (4, 5).

“Soil” problem 

Dark soil with grass.

Nowadays science shows that a diet plays a huge role in breast cancer development. Breast cancer was concluded to be obesity-related. One of the most influential factors of obesity is insulin.

Insulin is a hormone which is released by our pancreas every time when we eat in order to decrease rising levels of blood sugar (glucose) and absorb coming energy into the cells. The main role of insulin production in the body belongs to our dietary choices. When we consume a lot of carbohydrates (especially refined ones) and lean protein and repeat it frequently, our body is forced to metabolise coming sugar quicker by releasing a big amount of insulin.

Excessive, frequent and unhealthy eating leads to a condition where you have high levels of insulin in the blood all the time, it is called hyperinsulinemia. This state works as fertilized “soil” for breast cancer “seeds” and doubles the risk of the disease (6). If you don’t change your lifestyle and diet, at some point, you will likely develop hyperinsulinemia even if you are not overweight (7). 

“Seed” problem

Seeds lying in open hands.

All the tissues in our body have insulin receptors, including breast tissue. The problem with breast cancer cells is that they have six times more insulin receptors than normal cells, we can call it the “seed” problem. The more insulin receptors a cell has, the more the cell is able to get in glucose (blood sugar) for growth (8). High insulin levels can promote cancer growth.

Cancer cells use an inefficient pathway of producing energy called glycolysis. This way doesn’t require oxygen, but it leads to the generation of only two ATP (energy currency), where the normal process with oxygen extracts thirty-six ATP. That’s why cancer needs a lot of glucose to grow and thrive (9). 

When you don't consume any food, you don’t stimulate insulin production, that’s why intermittent fasting shows great results in lowering insulin levels. In our article “How does intermittent fasting help with insulin resistance?” you can read more about this mechanism.

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How can you prevent breast cancer?

Having a healthy, active lifestyle and following a proper diet is the best way to lower the risk of breast cancer.

Live with a lack of sugar

Sweets in a small bowl.

When we are fasting, our blood glucose levels are low and kept in balance. Our body doesn't produce a lot of insulin, the leading cause of obesity and as a result breast cancer. Losing weight and keeping it off significantly lowers the risk of developing breast cancer (12).

The composition of a diet is also very important. We are in charge of our dietary choices and when we complement intermittent fasting with a proper diet, which helps to maintain a balanced glucose level in the blood, it means we make strong preventative steps towards breast cancer (13). 

We’ve learned that breast cancer needs a lot of glucose to develop due to its specific energy-producing pathway. If you keep your blood sugar levels low and balanced there is not enough fuel for the cancer cell to grow (14). 

Starvation as a treatment tool

Deciding together with your therapist, you can include intermittent fasting in your cancer treatment. As we already know, cancer cells need a lot of sugar to grow and thrive. When we fast, our body keeps blood glucose levels low and works on ketones made from burning fat. Lack of fuel might cause starvation of some cancer cells that can affect the development of the disease (15).

How can you prepare yourself for radiation therapy?

Radiation therapy is a part of breast cancer treatment. Radiotherapy damages fast growing and dividing cells. Intermittent fasting makes our body resilient to different stress factors and scientific studies show that having two-three days of fasting before radiation therapy protects normal cells from the damage, because in fasted state normal cells stop dividing.

Having said so, you can prepare your body for the therapy, which usually affects the whole body (16). But please talk to your doctor before making changes in your eating behavior.

The bottom line

Body composition and the diet can be promotional or preventive for breast cancer. 

Having a healthy body weight and keeping blood sugar and insulin low can lower the risk of breast cancer. A healthy diet and intermittent fasting are powerful tools to achieve this (17,18). 


What foods should I avoid if I have breast cancer?

Foods that are high in carbohydrates such as flour products, sweets and grains, raise blood glucose and insulin levels (19). Because breast cancer cells have many insulin receptors, high insulin levels can promote their growth. It is therefore recommended to avoid these kinds of foods.

Also, industrial seed oils such as corn oil and sunflower oil, and trans fats should be avoided because they are pro-inflammatory, which can promote cancer.

What foods should I avoid if I have estrogen-positive breast cancer?

Phytoestrogens, also called isoflavones, can stimulate the growth of estrogen-positive breast cancer. It is, therefore, recommended to avoid foods naturally high in phytoestrogens.

These include:

  • flaxseed
  • soy products as tofu, tempeh, soy milk, soybeans and edamame
  • beans and legumes including peanut 
  • grains
  • sesame seeds (20).


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  3. Fung J. M. D. “The Cancer code”. HarperCollins UK, Nov 12, 2020 - Health & Fitness
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  7. M. J. Gunter et al., “Breast Cancer Risk in Metabolically Healthy but Overweight Postmenopausal Women,” Cancer Research 75, no. 2 (2015): 270–74. doi: 10.1158/0008-5472.CAN-14-2317
  8. V. Papa et al., “Elevated Insulin Receptor Content in Human Breast Cancer,” Journal of Clinical Investigations 86 (1990): 1503–10.doi: 10.1172/JCI114868
  9. O. Warburg, F. Wind, and E. J. Negelein, “The Metabolism of Tumors in the Body,” General Physiology 8, no. 6 (March 7, 1927): 519–30.doi: 10.1085/jgp.8.6.519
  10.  Glick D., Barth S., Macleod K. F. Autophagy: cellular and molecular mechanisms. J Pathol. Author manuscript; available in PMC 2010 Nov 23. doi: 10.1002/path.2697
  11. Alirezaei M., Kemball C. C., Flynn C. T., Wood M. R., Whitton J. L., William B. Kiosses W. B. Short-term fasting induces profound neuronal autophagy. Autophagy. 2010 Aug 16; 6(6): 702–710.doi: 10.4161/auto.6.6.12376
  12. Teras L. R., Patel A. V., Wang M. Sustained Weight Loss and Risk of Breast Cancer in Women 50 Years and Older: A Pooled Analysis of Prospective Data. J Natl Cancer Inst. 2020 Sep; 112(9): 929–937. doi: 10.1093/jnci/djz226
  13. Rice M. S., Eliassen A. H., Hankinson S. E., Lenart E. B., Willett W. C., Tamimi R. M. Breast Cancer Research in the Nurses' Health Studies: Exposures Across the Life Course. Am J Public Health. 2016 Sep;106(9):1592-8. doi: 10.2105/AJPH.2016.303325. Epub 2016 Jul 26.DOI: 10.2105/AJPH.2016.303325
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  17. A. H. Eliassen et al., “Adult Weight Change and Risk of Postmenopausal Breast Cancer,” JAMA 296, no. 2 (July 12, 2006): 193–201. doi: 10.1001/jama.296.2.193.
  18. Thorburn A. Autophagy and Its Effects: Making Sense of Double-Edged Swords. PLoS Biol. 2014 Oct; 12(10): e1001967. doi: 10.1371/journal.pbio.1001967
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  20. Saljoughian M. Focus on Phytoestrogens. U. S. Pharmacist. December 20, 2007

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