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Intermittent Fasting & Cancer Risk

What is the current role of intermittent fasting in cancer risk, prevention, and treatment? Dr. Heather Fields explores the different types of fasting diets and what to watch out for when suggesting intermittent fasting to your patients at risk of cancer.
August 18, 2021
Heather E. Fields, MD

Several entities have put out their own guidelines for cancer prevention, but The American Cancer Society recommends getting lean without being underweight and avoiding weight gain. However, the diets required to do this are often limited in nutrition, increasing the risk of nutrient deficiencies.

I wanted to find the best overall diet health-wise, so I have researched the safety and efficacy of many diets, especially intermittent fasting.


There are many different types of intermittent fasting. The most popular for weight loss is where people limit their daily eating period to 8 hours, usually from 9 a.m. to 8 p.m. or 11 a.m. to 7 p.m.

OK, so how can you lose weight safely with intermittent fasting? What if we cut the time of restricted eating to make it be much more doable and have better adherence? Would the short-term overnight fasting lead to cancer?

The potential impact of overnight fasting on breast cancer prevention is illustrated in several observational studies led by Catherine Mamaroneck and a cohort of 2,419 women with a history of breast cancer.

Overnight fasting for less than 13 hours was associated with a 36 percent increased risk of recurrence and a 21 percent increased risk of dying from breast cancer.


Not all types of fasting have the same results, however. The method studied the most is alternate-day fasting, in which one only eats every other day, going a full 24 hours without food on the opposite days.

There's also the fasting-mimicking diet, studied and promoted by Dr. Valter Longo, which requires five days per month of eating very few calories. It's plant-based and includes small portions of soups, snacks, algae, and multivitamins. It's low in protein, sugar, and calories. And he's shown some evidence of decreased IGF-1.

And then there is the one meal-a-day plan: the Warrior Diet (or, as I call it, the Working Mom Diet) in which you fast all day long and then consume all your calories later.


I wanted to know if the time of day mattered for intermittent fasting. It's been proposed that fasting should really occur overnight to coincide with our circadian rhythms. But just this year, a small pilot came out to suggest otherwise.

An observational study looking at 14 people fasting for 30 days of Ramadan from dawn until dusk for about 14 hours found that daytime fasting was associated with an anti-cancer proteomic signature. Most of their evaluations reached statistical significance.

It was very impressive that a daytime fast with just 14 hours over 30 days can lead to such a robust response. The large tumor suppressor kinase, one that was upregulated significantly, and the amyloid-beta precursor protein, which is more of an Alzheimer's gene, were both significantly suppressed as well.  


The point is that there was an upregulation of key regulatory proteins, glucose and lipid metabolism, insulin signaling, circadian clock, DNA repair, skeletal remodeling, immune system, and cognitive function.

So the others concluded that this signature is protective against not only cancer but also metabolic syndromes and neurodegenerative disorders.

Ultimately, studies have shown that calorie restriction and intermittent fasting diets are comparable in weight loss and reduction in inflammation. However, intermittent fasting seems better for those with insulin sensitivity, and there's less concern for delayed wound healing, impaired immunity, and XDR Sarcopenia.


Preclinical work demonstrates that fasting itself can retard cancer growth as much as chemotherapy, but regardless, fasting combined with chemotherapy produces the greatest therapeutic effect.

To learn more about how intermittent fasting affects you in the long run, click here:

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