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You might have heard of fasting and other forms of dietary restrictions being promoted as a way to address side effects of cancer treatment and boost the body’s immunity. Different fasting regimens and supplements have been sold by websites and companies despite a lack of science supporting their use [i].

We know that some cancers, such as breast cancer, are sensitive to body fat composition and insulin sensitivity; thus, weight loss and fat loss through fasting have been proposed to help combat them [ii]. But is fasting safe, and does it actually support your body while you are undergoing cancer treatment? We review the science behind different types of fasting as they stand right now. 

Fasting: What is it?

Fasting implies a complete restriction of caloric intake [iii]; typically, only water and non-caloric beverages (such as coffee or tea without sugar or milk) would be allowed. 

Other forms of fasting-adjacent diets include:

Intermittent fasting: Refers to any alternating period of fasting and normal eating. There are different variations, such as: alternating eating days and complete fasting days, fasting on 1 or 2 days a week, or restricting eating window by hours in a day [iv]. Here, when you eat matters more than what you eat. 

Fasting-mimicking diets: Refers to very low-calorie diets (around 300-1100 calories per day), typically low in carbohydrates, low in protein, and high in unsaturated fat, designed to give you a modest supply of energy while creating a condition similar to fasting [v].

Night fast: Refers to the period of no caloric intake at night, typically from your last meal the day before to the first meal the next morning. Researchers can quantify this as the number of hours after subtracting the time between your first and last meal of the day from 24 hours [vi].

Fasting: How does it work?

The body has 3 main sources of energy, corresponding to the 3 main macronutrients: carbohydrate, fat, and protein. In simple terms, our body uses these three energy sources in order of preference, as follows: 

Carbohydrate (from bread, rice, oatmeal, sugar, etc.) is the preferred source of energy, and is the only source of energy that our liver and red blood cells can use. 

Once we use up the carbohydrate from our meals and the carbohydrate we store, our body begins to break down fat and convert it to ketones for energy. When your body uses ketones as the main source of energy, you are in ketosis. (If this sounds familiar, you probably have heard about this in regard to the ketogenic diet).

Once we use up our fat stores, muscle begins to be broken down into amino acids, which will then be converted to sugar molecules. This is the last resort, as we also need muscles for our daily activities (our heart is a muscle, so is our diaphragm which helps us breathe, and so are the skeletal muscles that help us get around). Therefore, we want to preserve muscle mass, or lean body mass, especially in times of illness such as cancer. Muscle mass can be used as an indicator of nutrition status. 

Fasting: Why are we interested?

Cancer cells and normal cells use energy differently, a concept scientists call the Warburg effect [iv, vii, viii]. Fasting forces cells to shift their energy usage, and this process may make normal cells more resilient while rendering cancer cells more vulnerable to damage by chemotherapy and radiation [iii, vii, viii]. This is the basis behind the hypotheses that fasting can have a beneficial effect in cancer patients. 

Fasting: What does the science say?

Small-scale human studies found that fasting, especially in the period after chemotherapy, can help reduce symptoms and promote cellular repair. Particularly, fasting in the few days after chemotherapy was observed to reduce fatigue, nausea, vomiting, diarrhea, abdominal pain, and mouth sores. Markers of cellular damage also appeared lower in patients who fasted after chemotherapy [vii]. It is important to note that these associations were observed in small samples of patients, and it is unclear whether it is fasting that causes these favorable outcomes. 

Research into intermittent fasting in cancer is still in its preclinical stages, mostly just in rodents and other models [ii]. Different rodent studies have found conflicting results, some even pointing to negative outcomes with regards to cancer. There is insufficient data to assume that it could be helpful in cancer, aside from being a tool for weight loss [iv].

Regarding fasting-mimicking diets, human studies found that they do not seem to interfere with treatment and can be safe and tolerated when carried out between chemotherapy treatment cycles. Favorable changes in metabolites and hormones are observed, but the data is insufficient to conclude that it can positively impact cancer treatment [ix].

Observational studies into night fasting found that women who are able to have a longer night fast have better control of their blood glucose [x] and a decreased risk of breast cancer recurrence [vi]

Fasting: Risks and side effects

It’s important to note that these restrictions carry risks: dietary restrictions can lead to malnutrition, sarcopenia (loss of muscle mass), or cachexia in cancer patients [i, v]. Early human studies typically exclude participants who are underweight or at risk of malnutrition [i], so the current data regarding these diets’ safety might not apply to them. Some participants in fasting studies have also had weight loss, some regained the weight, and some had to drop out of the study because of the loss [ix].

Compliance is another concern; studies have reported dropouts as participants are unable to follow or tolerate the diet. It can be hard to consistently follow a restrictive diet. Dietitians typically recommend patients to find a dietary pattern that is easy to maintain long-term. 

Fasting: Should we do it?

The short answer: probably not.

There is not enough research to support the use of fasting for cancer patients. Research on fasting, intermittent fasting, and fasting-mimicking diets for individuals with cancer is still in its infancy, and there is heightened concern about its impact on weight and muscle mass and potential interaction with treatment. We need to know what types of cancer, at what stages, and with what individual condition fasting is safe [i].

Cancer patients have increased energy and protein needs. It is important to obtain enough energy and prevent the body from resorting to muscles for energy needs. We should also remember that in addition to providing us with nutrients, food can also be a source of joy and culture, and a way to connect with our family and community. This can be especially helpful during times of increased psychological stress, such as during cancer treatment.

The American Cancer Society recommends eating plenty of food to accommodate the increased needs during treatment, as well as maintaining physical activity to lessen the side effects. For more recommendations, click here from the American Cancer Society.


[i] Caccialanza, R., Cereda, E., De Lorenzo, F. et al. To fast, or not to fast before chemotherapy, that is the question. BMC Cancer (2018) 18(1):337. doi: 10.1186/s12885-018-4245-5

[ii] Piersol, B. (2020). Intermittent fasting and breast cancer: What you need to know. Memorial Sloan Kettering Cancer Center. Retrieved September 16, 2022, from

[iii] Cancer and Fasting/Calorie Restriction. UCSF Osher Center for Integrative Health. Retrieved September 16, 2022, from

[iv] Clifton, K.K., Ma, C.X., Fontana, L., Peterson, L.L. Intermittent fasting in the prevention and treatment of cancer. CA Cancer J Clin (2021) 71:527–546. doi: 10.3322/caac.21694

[v] Nencioni, A., Caffa, I., Cortellino, S., Longo, V.D. Fasting and cancer: Molecular mechanisms and clinical application. Nat Rev Cancer (2018) 18(11):707-719. doi: 10.1038/s41568-018-0061-0

[vi] Marinac, C.R., Nelson, S.H., Breen, C.I. et al. Prolonged nightly fasting and breast cancer prognosis. JAMA Oncol (2016) 2(8):1049-55. doi: 10.1001/jamaoncol.2016.0164

[vii] Plotti, F., Terranova, C., Luvero, D. et al. Diet and chemotherapy: The effects of fasting and ketogenic diet on cancer treatment. Chemotherapy (2020) 65(3-4):77-84. doi: 10.1159/000510839.

[viii] de Groot, S., Pijl, H., van der Hoeven, J.J.M. et al. Effects of short-term fasting on cancer treatment. J Exp Clin Cancer Res (2019) 38, 209. doi: 10.1186/s13046-019-1189-9

[ix] Vernieri, C., Fucà, G., Ligorio, F. et al. Fasting-mimicking diet is safe and reshapes metabolism and antitumor immunity in patients with cancer. Cancer Discov (2022) 12 (1): 90–107. doi: 10.1158/2159-8290.CD-21-0030[x] Marinac, C.R., Natarajan, L., Sears, D.D. et al. Prolonged nightly fasting and breast cancer risk: Findings from NHANES (2009-2010). Cancer Epidemiol Biomarkers Prev (2015) 24 (5): 783–789. doi: 10.1158/1055-9965.EPI-14-1292

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Susan started Savor Health after losing a close friend to a brain tumor and, through that experience, becoming aware of the significant unmet nutritional needs of people with cancer.  Struck by the fact that her friend was told “nutrition doesn’t matter” and “eat whatever you want,” Susan read the evidence-based literature on the subject, interviewed oncologists, oncology nurses and oncology dietitians, as well as patients and caregivers, and found that, in fact, nutrition does matter in oncology. Armed with solid scientific evidence supporting the clinical and quality of life benefits of proper nutrition, Susan left Wall Street and created Savor Health, an AI-based provider of personalized and clinically appropriate nutrition solutions for cancer patients, their caregivers and health enterprises. Susan brings to Savor Health over 25 years of industry experience in healthcare and business as well as expertise in strategy, finance and management.

Susan is an outspoken and tireless advocate for cancer patients receiving proper nutrition and nutrition support before, during and after treatment. She strongly believes that the U. S. healthcare system requires new innovation to transform it into a more holistic and integrated system of care whereby multiple disciplines coordinate care together for the benefit of the whole patient. As part of this, her goal is for nutrition to be an integral component of such an integrated cancer care delivery system.  Susan’s commitment to the field of oncology extends beyond Savor Health to volunteer work at Memorial Sloan Kettering Cancer Center in pediatrics and as a runner for Fred’s Team to raise money for research at Memorial Sloan Kettering. Susan participated in the Cancer Moonshot in June of 2016 where she was a breakout session group “igniter” tasked with starting and leading discussion. Susan’s first book, the Meals to Heal Cancer Cookbook, was published in March 2016.

In addition to her role as CEO of Savor Health, Susan speaks nationally about the importance of ensuring proper nutrition in the cancer patient and on topics including leadership and startups. She has been a speaker at the Harvard Medical School’s Career Advancement and Leadership Skills for Women in Healthcare, ESMO World Congress on GI Cancer, BioPharm America, AARP Live @50+, Lake Nona Impact Forum, and IIR ePharma Summit.

Prior to starting Savor Health, Susan had a successful career on Wall Street as a healthcare services investment banker working at prestigious firms including Donaldson, Lufkin & Jenrette, Wasserstein Perella and Robertson Stephens. Susan earned a B.A. from Duke University and M.B.A. from the University of Virginia’s Darden Graduate School of Business.

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Marissa Buchan is a registered dietitian, with advanced practice certifications in Oncology Nutrition (CSO) and Clinical Research (CCRP). She received her Bachelor’s degree in Psychology from Duke University, and Master’s of Science degree in Clinical Nutrition from New York University. Marissa worked for 10 years at Memorial Sloan Kettering Cancer Center in both the clinical research and nutrition departments.  In addition to counseling patients before, during, and after cancer therapy, she spearheaded nutrition-research efforts for the bone marrow transplant service. She has co-authored over 20 articles and has a particular interest in the role of nutrition on the intestinal microbiota and its impact on patient outcomes. When Marissa’s not wearing her lab coat, she’s in her apron whipping up healthy and delicious recipes that you can find on her blog, Get Off Your Tush and Cook.

Marissa is Chief Operating Officer of Savor Health where she leads operations working with the technology, clinical, and business development teams and management. Prior to assuming the role of COO in March 2020, Marissa was Vice President, Clinical Research and Operations at Savor Health where she worked closely with Savor Health’s Chief Medical Advisor, Scientific Advisory Board, and Clinical Operations Team to evaluate, design and conduct clinical research.  She also counsels patients on oncology nutrition issues and contributes to the Company website’s clinical content.

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Dr. DeFrance has a unique background including clinical interventional cardiologist, chief medical officer, educator, outcomes researcher and entrepreneur. He has expertise in Lifestyle medicine in which he was board certified in 2020 and is highly interested in the prevention and reversal of chronic disease. Dr. DeFrance also has expertise in appropriate utilization of technology in medicine, healthcare economics, value-based metrics, and educational design and delivery. He worked as Chief Medical Officer for HealthHelp, one of the largest specialty benefit managers in the US, and led large teams of healthcare professionals in writing evidence based appropriate care guidelines and rule sets which improve the quality and safety of medicine for over 20 million people in the US while also creating sustained savings in healthcare. He has also designed clinical decision support systems that are currently in use helping to improve patient care.

In 2018 Dr. DeFrance founded MedMentor Education, a company that provides state of the art CME content using the latest in eLearning science and online delivery platforms. Dr. DeFrance is also the founder and President of Digimedica, a consulting and educational design and delivery company for healthcare professionals, hospitals, and universities. He is passionate about creating systems to optimize knowledge transfer and has won numerous awards for teaching excellence during his career. He is an expert in cardiovascular CT imaging and has taught more than 3,000 physicians how to perform and interpret cardiac CT nationally and internationally and has lectured extensively on this subject.

Dr. DeFrance has a stellar reputation in the medical field and continues work to improve the quality and safety of patient care in the US.

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Alyson is a registered nurse and is certified in oncology nursing (OCN) through the Oncology Nursing Society (ONS). She also has her certification as an ONS Biotherapy and Chemotherapy Provider. Alyson studied nursing at Thomas Jefferson University where she obtained her Bachelor’s of Science in Nursing (BSN). Since starting her nursing career in 2004, Alyson has had a strong dedication and commitment to oncology patients. She has worked inpatient specializing in Bone Marrow and Peripheral Blood Stem Cell Transplantation. Alyson currently works in outpatient oncology at the North Shore-LIJ Monter Cancer Center. Alyson is part of the clinical team at Savor Health where she counsels patients on oncology and oncology nutrition issues and contributes to website and other Savor Health content.

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Chelsey is a Registered Dietitian and Board Certified Specialist in Oncology nutrition (CSO). She completed her Dietetic Internship at Northwell Health, received her BS in Dietetics at the University of Wisconsin-Madison, and her MS in Nutrition at Stony Brook University’s School of Medicine. Chelsey works as an outpatient dietitian at Mount Sinai covering all of the downtown cancer services at Mount Sinai Beth Israel and Philips Ambulatory Care Center. Chelsey works with patients and families before, during and after treatment to optimize their nutrition through dietary counseling and support. Chelsey has experience counseling clients with a variety of diagnoses including breast cancer, lung cancer, prostate cancer, head & neck cancer, and more. Chelsey also enjoys sharing nutrition knowledge with her peers by running a monthly Employee Wellness program that showcases healthy topics, recipes and food demos.

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Michelle is a Registered Dietitian specializing in oncology. She works as a clinical dietitian at an ambulatory cancer center in New York City and is a consultant for Savor Health. She is passionate about educating oncology patients on the importance of nutrition during their fight against cancer and helping them to optimize their nutrition through all phases of treatment. Michelle received her Bachelor of Science degree in dietetics from the University of Wisconsin-Madison and her Master of Science degree in Clinical Nutrition from New York University.

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Denise Sievering is a Registered Dietitian who is board certified in Oncology Nutrition as well as Nutrition Support. A fluent Spanish speaker, Denise joined the Savor Health team to support Spanish speaking cancer patients and to continue to expand the Platform’s nutritional strategies and recommendations in Spanish. Denise holds a Bachelor of Science degree from Rutgers University, and completed her internship at New York Presbyterian Hospital (NYP). Denise started her career as a registered dietitian at NYP-Columbia University Medical Center, primarily covering inpatient Oncology units. Denise also holds a Master of Arts degree in Mental Health Counseling from New York University, and incorporates her advanced training in motivational interviewing and empathic listening in her patient encounters, particularly those whose lives have been forever changed by a cancer diagnosis. A New Jersey native, Denise now resides in sunny San Diego, CA where she works as a part-time outpatient Oncology dietitian at Scripps Health-MD Anderson Cancer Center, and also works as an inpatient dietitian at Kaiser Permanente. In her spare time, Denise can be found at a mom-and-pop taco shop, one of the many local craft breweries, and exploring her new city of San Diego with her husband and her rescue pup, Ripley.

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Karen is a Registered Dietitian, Board Certified Specialist in Oncology Nutrition and registered in New York as a Certified Dietitian Nutritionist. Fluent in Spanish, Karen joined the Savor Health team to support Spanish speaking cancer patients and to continue to expand the Platform’s nutritional strategies and recommendations in Spanish. Karen received her Bachelor of Science degree from Ithaca College and her Master of Science degree from Hunter College. She works as an outpatient oncology dietitian in New York. Karen often works with local community centers to host nutrition programs for cancer survivors and their families, leading classes on how to live healthier lifestyles throughout their continuum of care. The American Institute of Cancer Research selected to showcase one of her many programs at their conference in 2019. Karen has written for and lent commentary to various publications and truly enjoys teaching people how to eat better. She loves to cook and strongly feels that healthy food doesn’t have to taste bad.

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Allie is a Registered Dietitian and a Certified Specialist in Oncology (CSO). She joins Savor in 2023, bringing years of experience from the John Theurer Cancer Center in New Jersey, where she worked with patients with a variety of cancers. Her goal is to help people feel their best, both mentally and physically, when physical health challenges arise. She believes in the power of nutrition ever since the impact it made on her athletic career as a volleyball player during college. Allie graduated with her Bachelor of Science degree from University of Maryland-Baltimore County and has her Master’s degree in Human Nutrition from the University of Wisconsin Stout. She enjoys travelling, enjoying different cuisines, cooking, and hiking and other outdoor activities with her family and dog.

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Julia Penberg is a seasoned healthcare professional with more than 30 years of experience focusing on maximizing operational excellence, leading clinical program development and building strong cross-functional teams. Her previous roles include overseeing the performance of clinical managers and nurse practitioners across multiple markets within United Healthcare-Optum’s Medicare Advantage and dual-eligible special needs populations, payer outreach and program development at Mayo Clinic, ground level specialty hospital development and direct patient care as a family and dermatology nurse practitioner. Julia volunteered as an operating room nurse and nurse practitioner on several mission trips to Romania and was a support group leader for the Kansas City chapter of the International Myeloma Foundation. Her motivation throughout her career has been with wellness promotion, disease risk modification and ensuring the best patient experience across the health continuum. Ms. Penberg received an MBA from the University of Dallas; a MS in Nursing from the University of Kansas and a BS in Nursing from the University of Texas-Austin. She is board certified as a Family Nurse Practitioner.

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Rachel is a Registered Dietitian and Board Certified Specialist in Oncology Nutrition (“CSO”). She joined NYP-Columbia as the outpatient oncology dietitian in 2020 after working at Jamaica Hospital Medical Center for two years. Rachel completed her dietetic internship through Keene State College in 2017. She is pursuing an MS in Integrative Nutrition at Stony Brook University and has a BS in Human Nutrition, Foods and Exercise from Virginia Tech. Rachel provides nutrition counseling to all types of oncology patients and helps them understand the mental and physical benefits of nutrition as an ally in their fight against cancer. In her free time she enjoys slow meals with family and friends, Pilates, and tending to her fire escape garden.

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Allie Werner is a Registered Dietitian at Fresenius Kidney Care where she provides medical nutrition therapy diet counseling to patients on Dialysis. She received her Bachelor’s Degree in nutrition from Indiana University and completed her Master’s Degree and dietetic internship at Loyola University Chicago. In her free time she enjoys spending time with friends and family, checking out the amazing food scene in downtown Chicago, and exercising on her Peloton bike.

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Immersed in the tech world for a decade, I've coded, led teams, and honed my skills in architecture and design. As a tech enthusiast, I've seamlessly woven through full-stack projects, fusing my love for code with the art of leadership.

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Mohit is a full-stack developer with expertise in Python and JavaScript, known for his efficient coding and ability to deliver scalable software solutions. His technical contributions are highlighted on GitHub and Stack Overflow, demonstrating his commitment to the tech community and problem-solving skills. With a solid educational foundation and a diverse project portfolio, Mohit excels at navigating complex challenges and is well-equipped to contribute to dynamic software projects.

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Rayna McCann is a Registered Dietitian and Board Certified Specialist in Oncology Nutrition. She is a Registered Yoga Teacher and yoga4cancer certified. She received her BS in Nutrition at Penn State University and her MS from Stony Brook University. For work, Rayna wears many hats in the world of nutrition and worked for years in clinical settings focusing on oncology nutrition. She is also an Adjunct Professor and passionate about inspiring the future of dietitians. Throughout her career, she has received awards recognizing her dedication to patient safety and her contributions to improving malnutrition awareness. In 2022, Rayna was proud to accept the ‘Dietitian of the Year’ award through the Long Island Academy of Nutrition and Dietetics. Rayna has co-authored abstracts for poster presentations within the American Institute for Cancer Research conference, as well as, the Nutrition and Dietetics Food and Nutrition Conference Expo and subsequent publication. She has enjoyed authoring articles, including an article for The Cure magazine regarding Multiple Myeloma and nutrition. When Rayna is not participating in nutrition related activities, she is dedicated to dog rescue.

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