Fasting during Chemotherapy & Other Chronic Illnesses

by Dr. Edison de Mello

It Boosts Immunity & It likely minimizes the side effects of chemotherapy, making it more effective.

Let's start by describing the difference between calorie restriction (CR) versus intermittent fasting (IF). Calorie restriction involves limiting food consumption, while fasting involves not eating for varying lengths of time. A vast body of research shows that fasting has been used as a therapy for many different conditions and a part of spiritual/religious practices throughout history.

"intermittent fasting can promote diversity of gut bacteria, leading to positive brain/mood changes and better sugar Balancing." - E. de Mello (Bloated Book)

In general, intermittent fasting involves an eating plan that switches between periods of not eating and eating on a regular schedule. There are many different intermittent fasting schedules. For example, some diets suggest fasting entirely for a day and then regularly eating for the next three days, while others suggest eating only during specific times of the day – for example, from 8 am to 5 pm, and eating nothing at other times. 

Increased Blood Sugar is dangerous.

The key to the protective factor in fasting during chemotherapy may be a genetic signaling glucose pathway called PKA/EGR1. This pathway in mammalian cells, including heart cells, is similar to regulating cellular protection and aging.

Previous studies have shown that high glucose levels combined with chemotherapy are associated with an increased risk of developing complicated infections and a significant increase in overall mortality. Therefore, practitioners should avoid recommending a combination of drugs that promote hyperglycemia and chemotherapy. Fasting might reduce fatigue and improve cognition, especially in the first eight days after chemotherapy. To better understand fasting timing during chemotherapy.

How does fasting or calorie restriction help fight cancer making treatment MORE effective? 

Current research indicates that a fasting-like diet may benefit some chemotherapy patients because it counteracts increases in blood sugar caused by chemotherapeutic drugs, protecting healthy cells from becoming too vulnerable to chemotherapy. Increased blood sugar caused my most chemotherapeutic agents are believed to increase healthy cells' vulnerability and subsequent death, referred to as apoptosis. However, it is important to note that high protein intake is associated with increased growth hormone.

"A short-term diet change may counteract increases in blood sugar and possibly protect healthy cells – Valter Longo, director of the USC Longevity Institute.  

Calorie restriction (CR) or intermittent fasting (IF) is now believed to be more protective and less concerning for weight loss. Researchers have divided metabolic stages during calorie restriction or fasting into three stages: Glycogen, lipid, and amino acid. As blood glucose levels fall during fasting, the pancreas secretes increased amounts of glucagon. This action also reduces insulin secretion, which in turn decreases glucose storage in the form of glycogen.

The first phase usually lasts about ten hours and utilizes glycogen stores for energy; The second phase lasts several hours when these nutrients create ketones, which the body and brain use for energy. A ketogenic diet is only advised if calories and other essential nutrients continue to be consumed because once the fat reserves are diminished, muscle breakdown begins to fuel gluconeogenesis.

Unlike CR, fasting increases cell protection from oxidative stress and prevents weight loss. It results in a more significant drop in insulin levels and an increase in insulin sensitivity in a shorter time than CR. This is clinically significant because insulin levels play a critical role in cancer risk, and cancer cells do not respond to the protective signals generated by fasting, which leaves them more vulnerable to cancer treatment.


Fasting Strengthens Immunity 

Adaptation to starvation requires an organism to divert energy into multiple protective systems to minimize the damage that would reduce fitness. It is thought that these systems can also prolong life and decrease cancer risk. Calorie restriction (CR) without malnutrition is the most potent and reproducible physiological intervention for increasing lifespan and protecting against cancer. CR has been shown to reduce anabolic hormones, growth factors, and inflammatory cytokines, reduce oxidative stress and cell proliferation levels while enhancing cell destruction (autophagy), and several DNA repair processes.

Fasting and CR can slow and even stop cancer progression, kill cancer cells, boost the immune system, and significantly improve the effectiveness of chemotherapy and radiation therapy.


Risk Reduction and Tumor Regression

Researchers at the University of Southern California demonstrated in a study published in 2014 that fasting led "old" immune cells to die in mice and were replaced by stem cells as soon as the subjects recommenced eating.

A study published in 2017 showed that alternate-day fasting, in which one-day calories stayed at 400 for women and 600 for men, and the other day was unregulated, reduced blood levels of glucose, insulin, and growth hormone. Long-term risk reduction of chronic diseases including cancer, diabetes, and cardiovascular disease was decreased. 

A recent study analyzed the Women's Healthy Eating and Living study data. It showed that breast cancer survivors who didn't eat for at least 13 hours overnight had a 36% reduction in the risk of recurrence and were 21% less likely to experience breast cancer-related mortality. The proposed mechanism for this finding is related to better glycemic control resulting in protection against carcinogenesis. Each 2-hour increase in nightly fasting was linked to progressively lower hemoglobin A1C levels. This research is exciting because it is a dietary strategy that most people could implement.


Protection from Treatment-Related Side Effects

Fasting may also protect patients against the harmful side effects of chemotherapy or radiation therapy. Fasting for up to five days, followed by a regular diet before treatment, is believed to reduce side effects without chronic weight loss, and it does not negatively interfere with treatment. Cancer patients who voluntarily underwent short-term fasting before and after chemotherapy reported fewer side effects, including decreased fatigue, weakness, and gastrointestinal side effects.



  1. Comparing the research between CR and fasting, fasting seems to provide more dramatic results and protect healthy cells without the risk of weight loss or immune suppression. Both CR and IF are the subjects of ongoing research, and definitive conclusions await the results of those studies. As mentioned above, fasting may not be appropriate for everyone, especially those underweight or very ill. And, particularly in patients with cancer. IF or CR, if appropriate in any patient with cancer any medical condition should ALWAYS be under the supervision of a licensed health care practitioner.
  1. Change your health habits for life. Give your body a Summer Head-Start. Akasha’s Reset Program helps you restore your body’s natural ability to wellness through a safe pre-summer detox so that you can look and feel your best EVER. Check it out:


But for cancer treatment, fasting can also put you at risk of not getting enough critical nutrients. Cancer treatment requires plenty of energy, protein, vitamins, and minerals to help your body best cope. Having a proper BMI (body mass index) is essential for preventing many types of cancer. Therefore, you must seek medical supervision before embarking on ANY CR or IF while undergoing cancer treatment. 

The take-home message:

  1. An anti-inflammatory diet must contain plenty of colorful fruits, vegetables, beans, lentils, herbs, and spices.

  2. Low glycemic starches only is a must.

  3. Healthy fats at every meal, including good sources of Omega-3s.

  4. Moderate protein intake of 3-4 ounces per meal from a combination of animal and plant proteins.

  5. Lengthen the time between dinner and breakfast to allow for a longer overnight fast, with the goal of 13 or more hours, for example, dinner by 6:00 pm and breakfast after 7:00 am.

  6. Short-term water fasts of 1-3 days could help re-generate the immune system and increase cellular protection against oxidative stress. Working with a healthcare provider, you can determine how often it may be appropriate for you to engage in a fast.

  7. If you are a cancer patient, water fasting 2-3 days before treatment and up to one day following treatment to optimize the efficacy of treatment and reduce treatment-related side effects may be considered, but only under the supervision of a qualified practitioner.


About the Author:

Edison de Mello MD, Ph.D. -  Founder and Chief Medical Officer of the Akasha Center for integrative Medicine is a board-certified integrative physician with over 25 years of experience in the field of Integrative Medicine. His recent book, BLOATED? Outlines Dr. de Mello's approach to medical care. With his signature approach, "I meet my patients before I meet their diseases," Dr. de Mello has helped thousands of patients across the globe. 



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  5. Cheng CW, Adams GB, Perin L, et al. Prolonged fasting reduces IGF-1/PKA to promote hematopoietic-stem-cell-based regeneration and reverse immunosuppression. Cell stem cell 2014;14:810-23.
  6. Ong KR, Sims AH, Harvie M, et al. Biomarkers of dietary energy restriction in women at increased risk of breast cancer. Cancer prevention research (Philadelphia, Pa) 2009;2:720-31.
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