Fasting During Cancer Treatment: What You Need to Know

Disclaimer: This resource is for informational purposes only. It is not a substitute for personalised medical advice. All individuals are strongly advised to consult with their treating medical team before making any dietary or treatment-related changes. Nutritional and fasting approaches must be tailored to individual medical conditions and care plans.

What Is Fasting?

Fasting refers to voluntarily abstaining from food or significantly reducing caloric intake for a defined period. There are several types of fasting, each with varying implications for people with cancer:

• Water or liquid fasting – consuming only fluids such as water, herbal teas or broths
• Time-Restricted Eating (TRE) – eating within a fixed window each day (e.g. 8 hours of eating, 16 hours fasting)
• Fasting Mimicking Diet (FMD) – a very low-kilojoule, plant-based diet over 4 to 5 days designed to mimic fasting without complete food restriction
• 5:2 Diet – eating normally for five days and fasting or severely restricting kilojoules for two non-consecutive days

What Does the Research Say About Fasting and Cancer?

Fasting is not yet a standard component of cancer treatment in Australia, but emerging studies suggest potential benefits—particularly when fasting is carefully timed around chemotherapy.

Short-Term Fasting (24 to 72 hours) is being studied for its potential to:

• Reduce the severity of chemotherapy-related side effects
• Protect healthy cells while leaving cancer cells more vulnerable to treatment (a process known as differential stress resistance)
• Improve treatment tolerance without compromising nutritional status when monitored correctly

Fasting Mimicking Diets may:

• Preserve lean body mass during treatment
• Improve metabolic markers linked to cancer progression
• Reduce inflammation and oxidative stress
• Support ketosis, a metabolic state that may inhibit some types of cancer growth

Who Might Be a Good Candidate for Fasting During Treatment?

Fasting may be suitable for patients who:

• Have a Body Mass Index (BMI) greater than 18.5 and are maintaining a stable weight
• Are not experiencing cachexia or rapid unintentional weight loss
• Have good functional status 
• Are highly motivated, psychologically prepared, and under professional supervision

Fasting is not recommended for patients who:

• Are underweight or malnourished
• Are pregnant 
• Are elderly and frail
• Are managing comorbidities such as diabetes, renal disease, or gastrointestinal conditions
• Are experiencing significant fatigue or treatment-related muscle wasting
• Are required to take medication with meals
• Have a previous history of eating dysregulation disorders

Nutritional and Safety Considerations

Fasting is not without risks. Potential concerns include:

• Loss of lean muscle mass
• Fatigue or reduced energy levels
• Electrolyte imbalances
• Micronutrient deficiencies
• Delayed recovery or impaired immune function

Strategies to Reduce Risk:

• Use fasting mimicking diets instead of total fasts
• Monitor weight, muscle mass, and treatment side effects
• Supplement with electrolytes and micronutrients
• Carefully reintroduce protein and kilojoules after fasting
• Seek support from a dietitian or clinical nutritionist experienced in oncology nutrition

Biomarkers to Monitor

During any fasting protocol, monitoring may include:

• Weight, Body Mass Index (BMI), and lean body mass
• Blood glucose, insulin, and Insulin-like Growth Factor 1 
• Electrolytes, liver and kidney function
• Albumin and prealbumin levels
• Treatment tolerance, including blood counts, fatigue and nausea

What If Fasting Is Not Right for You?

Alternative approaches include:

• Time-Restricted Eating (such as a 12-hour or 14-hour overnight fast)
• Mediterranean-style diets high in whole grains, olive oil, vegetables, and legumes
• Light, easy-to-digest meals before chemotherapy
• Nutrient-dense meals high in protein and antioxidants post-treatment
• Protein-sparing modified fasts under professional guidance

Final Considerations and Practical Advice

• Weigh up the pros and cons of fasting for yourself - check out the resources below
• Start slowly: test any fasting approach on non-treatment days
• Always work in collaboration with your oncology and nutrition teams
• Have a clear plan for hydration, electrolytes, and refeeding
• Adjust your approach based on how your body responds
• Do not persist with fasting if you feel unwell or experience adverse effects

Useful Resources 

1. _{Cortellino S, et al. Fasting mimicking diet in mice delays cancer growth and reduces immunotherapy-associated cardiovascular and Systemic Side Effects. Nat Commun. 2023; 14(1). Doi: 10.1038/s41467-023-41066-3 https://pubmed.ncbi.nlm.nih.gov/37684243/}
2. _{de Groot S, Vreeswijk MP, Welters MJ, Gravesteijn G, Boei JJ, Jochems A, et al. The effects of short-term fasting on tolerance to (neo) adjuvant chemotherapy in HER2-negative breast cancer patients: a randomized pilot study. BMC Cancer. 2015; 15:652 https://bmccancer.biomedcentral.com/articles/10.1186/s12885-015-1663-5}
3. _{Dorff TB, Groshen S, Garcia A, Shah M, Tsao-Wei D, Pham H, et al. Safety and feasibility of fasting in combination with platinum-based chemotherapy. BMC Cancer. 2016 Jun 10; 16:360. doi: 10.1186/s12885-016-2370-6. PMID: 27282289; PMCID: PMC4901417 https://bmccancer.biomedcentral.com/articles/10.1186/s12885-016-2370-6} 
4. _{Ferro Y, Maurotti S, Tarsitano MG, Lodari O, Pujia R, Mazza E, et al. Therapeutic Fasting in Reducing Chemotherapy Side Effects in Cancer Patients: A Systematic Review and Meta-Analysis. Nutrients. 2023 Jun 8; 15(12):2666. doi: 10.3390/nu15122666. PMID: 37375570; PMCID: PMC10303481.}
5. _{Gabel K, Cares K, Varady K, Gadi V, Tussing-Humphreys L. Current Evidence and Directions for Intermittent Fasting During Cancer Chemotherapy. Adv Nutr. 2022 Mar;13(2):667-680. doi: 10.1093/advances/nmab132. PMID: 34788373; PMCID: PMC8970823 https://pubmed.ncbi.nlm.nih.gov/34788373/} 
6. _{Koppold-Liebscher D, Kessler CS, Steckhan N, Bähr V, Kempter C, Wischnewsky M, et al. Short-term fasting accompanying chemotherapy as a supportive therapy in gynecological cancer: protocol for a multicenter randomized controlled clinical trial. Trials. 2020 Oct 15; 21(1):854. doi: 10.1186/s13063-020-04700-9. PMID: 33059765; PMCID: PMC7559781 https://pubmed.ncbi.nlm.nih.gov/33059765/} 
7. _{Safdie FM, Dorff T, Quinn D, Fontana L, Wei M, Lee C, et al. Fasting and cancer treatment in humans: A case series report. Aging (Albany NY). 2009 Dec 31; 1(12):988-1007. doi: 10.18632/aging.100114. PMID: 20157582; PMCID: PMC2815756 https://pubmed.ncbi.nlm.nih.gov/20157582}
8. _{Sun L, Li YJ, Yang X, Gao L, Yi C. Effect of fasting therapy in chemotherapy-protection and tumor-suppression: a systematic review. Transl Cancer Res. 2017; 6(2):354-365 https://doi.org/10.21037/tcr.2017.03.35} 
9. _{Tiwari S, Sapkota N, Han Z. Effect of fasting on cancer: A narrative review of scientific evidence. Cancer Sci. 2022 Oct; 113(10):3291-3302. doi: 10.1111/cas.15492. Epub 2022 Aug 10. PMID: 35848874; PMCID: PMC9530862 https://pubmed.ncbi.nlm.nih.gov/35848874/} 
10. _{Zorn S, Ehret J, Schäuble R, Rautenberg B, Ihorst G, Bertz H, et al. Impact of modified short-term fasting and its combination with a fasting supportive diet during chemotherapy on the incidence and severity of chemotherapy-induced toxicities in cancer patients - a controlled cross-over pilot study. BMC Cancer.2020 Jun 22;20(1):578. doi: 10.1186/s12885-020-07041-7. PMID: 32571329; PMCID: PMC7310229 https://pubmed.ncbi.nlm.nih.gov/32571329/}

Fasting mimicking diets

https://www.uclahealth.org/news/article/fast-track-health-inside-fasting-mimicking-diet

https://mydr.com.au/tests-investigations/fasting-mimicking-diets-fmd/

https://www.healthline.com/nutrition/fasting-mimicking-diet#takeaway

Support and Community

You do not have to navigate cancer and nutrition alone. At The NutraThrive Collective, we provide evidence-based programs, resources and professional support for patients and carers affected by cancer—before, during and after treatment. Come and join our community of patients, carers and professionals! 

Thanks for reading!

A/Professor Teresa Mitchell-Paterson