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Intermittent Fasting May Help Cancer Treatments Work Better, Small, Early Study Suggests

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A small study suggests that a specific type of intermittent fasting is safe and possible for people diagnosed with cancer, and it may boost the effectiveness of certain cancer treatments. It’s the first time this type of intermittent fasting — called a “fasting-mimicking” diet — has been studied in people, the researchers said.

The research was published online on Nov. 17, 2021, by the journal Cancer Discovery. Read the abstract of “Fasting-mimicking diet is safe and reshapes metabolism and antitumor immunity in cancer patients.”

About intermittent fasting
About the study
What this means for you

About intermittent fasting

In general, intermittent fasting is a type of eating plan that switches between periods of not eating and eating on a regular schedule.

There are many different intermittent fasting schedules. For example, with some diets, you fast completely for a day, and then eat regularly for the next three days. With other diets, you eat only during specific times of the day, say from 8 a.m. to 5 p.m., and eat nothing at other times.

In this study, the researchers looked at an intermittent fasting schedule called a fasting-mimicking diet. The diet involved five days of eating very few calories, followed by about three weeks of regular eating.

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About the study

Preclinical studies in mice have suggested that intermittent fasting may help cancer treatments work better. In this study, the researchers tested this particular type of intermittent fasting schedule in people diagnosed with cancer for the first time. Their main goal was to see if a fasting-mimicking diet was safe and possible for people diagnosed with cancer to follow. The researchers also analyzed how the diet affected certain blood markers.

The study included 101 people — 73 women and 28 men — diagnosed with cancer:

  • 56 people were diagnosed with breast cancer
  • 10 people were diagnosed with colorectal cancer
  • seven people were diagnosed with lung cancer
  • four people were diagnosed with prostate cancer
  • three people were diagnosed with pancreatic cancer
  • three people were diagnosed with melanoma
  • three people were diagnosed with reproductive cell cancers
  • two people were diagnosed with ovarian cancer
  • two people were diagnosed with thyroid cancer
  • two people were diagnosed with chronic lymphocytic leukemia
  • two people were diagnosed with non-Hodgkin lymphoma
  • one person was diagnosed with uterine cancer
  • one person was diagnosed with a sarcoma, a tumor in the connective tissues
  • one person was diagnosed with multiple myeloma, cancer that forms in a type of white blood cell
  • one person was diagnosed with stomach cancer
  • one person was diagnosed with kidney cancer
  • one person was diagnosed with mesothelioma, cancer in the lining of the lungs caused by inhaled asbestos fibers
  • one person was diagnosed with myelofibrosis, an uncommon type of bone marrow cancer

The fasting-mimicking diet was made up of two parts:

  • For five days, people ate a plant-based, low-carbohydrate, low-protein, calorie-restricted diet. On day one, people could eat up to 600 calories. On days two through five, people could eat up to 300 calories. For comparison, 1 cup of brown rice contains about 216 calories and 1 cup of broccoli contains about 31 calories. The people received a list of foods and beverages — with specified maximum amounts — they could eat during these five days.
  • For 16 to 23 days after the five low-calorie days, the people could eat whatever they liked, but were advised to follow guidelines for a healthy diet.

So each fasting-mimicking diet cycle ranged from 21 to 28 days. The length of each person’s cycle was based on when they were receiving cancer treatment; people were not on the five-day restricted calorie part of the diet while they were receiving treatment.

The people in the study completed up to eight consecutive cycles of the fasting-mimicking diet.


  • 99% of the people completed at least one cycle
  • 76.2% of the people completed at least three cycles
  • 19.8% of the people completed eight cycles

The researchers collected blood samples from the people in the study before each cycle started and at the end of the five-day restricted calorie part of the cycle.

Overall, only 12.9% of the people reported side effects, which were mostly mild to moderate. Fatigue was the most common. Other side effects were:

  • low blood sugar (hypoglycemia)
  • fainting
  • nausea
  • dizziness
  • high liver enzymes

Most of the people lost weight during the five days of restricted eating, but gained it back during the second part of the cycle.

Side effects were few and mild, so the researchers concluded the fasting-mimicking diet was safe, well-tolerated, and possible in combination with standard cancer treatments such as chemotherapy, immunotherapy, and hormonal therapy.

The blood marker analysis included information from 99 people in the study. Overall, the fasting-mimicking diet:

  • reduced blood glucose levels by 18.6%
  • reduced blood insulin levels by 50.7%
  • reduced insulin-like growth factor 1 (IGF-1) levels by 30.3%

Research shows that high levels of blood glucose and insulin are linked to a higher risk of a number of cancers, including breast cancer. IGF-1 is a hormone that helps support cell growth and development, including cancer cells.

The researchers also reported results from a very early analysis of how the first calorie-restricted part of the diet affected the immune systems of 22 people diagnosed with breast cancer. This analysis was part of another ongoing study: the DigesT study.

For the DigesT study, the people followed the first five calorie-restricted days of the fasting-mimicking diet seven to 10 days before breast cancer surgery.

The researchers compared:

  • levels of tumor-infiltrating immune cells and activated immune marker genes in cancer tissue samples removed during biopsies before the people started the diet
  • levels of the same things in cancer tissue samples removed during surgery after the people completed the first five days of the diet

The analysis showed that levels of tumor-infiltrating immune cells were higher after the fast-mimicking diet. There were also changes in the activated immune marker genes, indicating that the immune system was beginning to recognize the cancer as something it should attack.

“Our results from a first-in-human clinical trial showed that a scheme of severe short-term calorie restriction was safe and biologically active in patients, and that its activity likely involved the activation of immune responses,” lead researcher Claudio Vernieri, MD, PhD, medical oncologist at Fondazione IRCCS Istituto Nazionale dei Tumori, in Italy, said in a statement. “Since calorie restriction is a safe, inexpensive, and potentially effective approach that could be easily combined with standard antineoplastic therapies, we think these findings might have relevant implications for cancer therapy.”

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What this means for you

The results of this study are very early, but seem promising. Still, it’s important to remember that it’s the first time this particular type of diet has been tested in people diagnosed with cancer. More research needs to be done before we know whether intermittent fasting can actually help activate the immune system to work with treatments to fight cancer.

Read more about Clinical Trials if you’re interested in being part of a study.

And stayed tuned to Research News for the latest information on diet and cancer.

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Written by: Jamie DePolo, senior editor

Reviewed by: Brian Wojciechowski, MD, medical adviser

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