New research — looking at both animal and human trials — suggests that a fasting diet may complement breast cancer therapies.

photo of women at breast cancer support meetingShare on Pinterest
New research suggests that a fasting diet may help boost the effects of breast cancer therapy.

A series of feasibility studies from an international team of researchers has found that a fasting diet may improve the efficacy of conventional breast cancer therapies.

The research — from both animal models and with the collaboration of human participants — now appears in the journal Nature.

It lays the groundwork for future studies to corroborate the initial findings and expand their applicability.

According to the American Cancer Society (ACS), around two-thirds of breast cancers are hormone receptor-positive. This means that the cancer makes use of the hormones estrogen and progesterone to grow.

One way of fighting these forms of cancer is through hormone therapy, also called endocrine therapy.

This type of therapy stops estrogen and progesterone from attaching to the tumor, which inhibits its growth. Doctors often use it after surgery when a patient typically takes it for a minimum of 5–10 years.

However, tumors can adapt to hormone therapy by developing resistance, and so reducing the efficacy of the treatment.

As a consequence, discovering ways of overcoming resistance to hormone therapy and improving its performance is valuable.

There is emerging evidence suggesting that short-term fasting could, in theory, be an effective complement to other cancer treatments.

One form of short-term fasting is the Fasting Mimicking Diet (FMD), which researchers used in the feasibility studies of females with breast cancer.

FMD lasts for 5 days each month and mimics the effect of fasting on a person’s metabolism. The diet provides limited but carefully balanced nutrition consisting of protein, fats, and carbohydrates.

According to recent research in the Journal of Experimental & Clinical Cancer Research, short-term fasting “reinforces stress resistance of healthy cells, while tumor cells become even more sensitive to toxins, perhaps through shortage of nutrients to satisfy their needs in the context of high proliferation rates and/or loss of flexibility to respond to extreme circumstances.”

However, there are only limited studies exploring whether the theory translates into practice.

The current research is the summation of a series of animal trials and clinical research in humans. The trials were only small feasibility studies designed to test whether the theory could, in principle, work in practice.

In the studies on mice, the researchers found that short-term fasting reduced blood insulin, insulin-like growth factor 1 (IGF1), and leptin. These effects appeared to improve the efficacy of tamoxifen and fulvestrant, two drugs doctors use in hormone therapy.

As well as making the drugs more effective, the metabolic changes that fasting induced also reduced the tumor’s ability to adapt to the hormone therapy.

In the human clinical studies, the researchers looked to see whether similar short-term fasting would produce comparable metabolic changes.

After analyzing the results, they also saw a reduction in blood insulin, IGF1, and leptin.

According to Prof. Valter Longo, the study’s co-senior author and the director of the Longevity Institute at the University of Southern California Leonard Davis School of Gerontology, “[o]ur new study suggests that a fasting-mimicking diet together with endocrine therapy for breast cancer has the potential to not only shrink tumors but also reverse resistant tumors in mice.”

“We have data that for the first time suggests that a fasting-mimicking diet works by changing at least three different factors: IGF1, leptin, and insulin,” he adds.

According to Dr. Alessio Nencione of the Department of Internal Medicine and Medical Specialties, University of Genoa, Italy, and the corresponding author of the research, if the short-term fasting proves to be effective in humans then it is likely to be relatively safe:

“Some patients followed monthly cycles of the fasting-mimicking diet for almost 2 years without any problems, suggesting that it is a well-tolerated intervention. We hope this means that this nutritional program that mimics fasting could one day represent a weapon to better fight cancer in patients receiving hormone therapy without serious side effects.”

Having demonstrated that similar metabolic changes appear to occur in human participants and mice, further research can now explore whether the changes also improve the efficacy of hormone therapies in humans.

In separate research that the study’s authors contributed to, a short-term fasting diet appeared to help improve the efficacy of chemotherapy in humans. The authors are hopeful that further research can demonstrate the same for hormone therapy.

According to Prof. Longo, “[t]he results in mice are very promising. And the early clinical results show potential as well, but now we need to see it work in a 300- to 400-patient trial.”

“I like to call it the nontoxic wildcard for cancer treatment. These clinical studies we have just published — together with the many animal studies published in the past 12 years — suggest that cycles of the fasting-mimicking diet [have] the potential to make standard therapy more effective against different cancers, each time by changing a different factor or nutrient important for cancer cell survival.”