The link between fasting and cancer continues to be a topic of mass discussion, but does fasting really have an impact on cancer prevention and treatment?
Cancer care is developing at an exceedingly high rate, yet deaths remain high. In fact, cancer (particularly lung cancer) is one of the leading causes of death in the UK1. Some of these deaths could be avoidable, with many cancers linked to modifiable risk factors.
According to Cancer Research UK and the World Cancer Research Fund, around 40 per cent of cancer cases in the UK each year are considered preventable2,3. This highlights a potential opportunity to reduce cancer rates and outcomes by promoting healthy lifestyle changes that can lead to a longer and healthier lifespan.
Read on to learn about the connection between fasting and cancer and how it might affect your overall well-being.
What Do We Mean by Fasting?
Fasting is the practice of abstaining from eating (and sometimes drinking) for a period of time. It focuses on when you eat as opposed to what you eat. Although it has recently grown in popularity, it has been practised among many cultures and religions for thousands of years.
The role of fasting in health and disease is also not a new concept and has been described in ancient Greece, where fasting was advocated by Hippocrates as a method of treating illness4.
What Are Different Types of Fasting?
Intermittent Fasting
Intermittent fasting involves fasting cycles, which relate to abstaining from eating food on alternate days or periodically. There are many different regimens, for example, the 5:2 diet. This involves a calorie restriction to 25 per cent of normal calorie intake for two non-consecutive days and normal calorie consumption for the remaining five days5.
Time Restricted Feeding
This type of fasting involves limiting the consumption of food to a specific period of time. For example, all calories are typically consumed within 4-12 hours6. There is no calorie restriction.
Prolonged Fasting
This refers to fasting periods lasting more than 24 hours.
Fasting-Mimicking Diet
A fasting-mimicking diet (FMD) is slightly different from those listed above. FMD involves a five-day periodic diet that causes the body to enter a fasting mode without complete abstinence from eating.
FMD is usually a low-carbohydrate, low-protein, and low-calorie diet over 4-7 days. Professor Valter Longo is at the forefront of research into fasting-mimicking diets and their effect on disease processes and longevity.
The results from a randomised clinical trial carried out by Professor Longo indicated that FMD reduces risk factors and markers associated with ageing and disease, although larger studies are required to confirm the findings7.
How Is Fasting Different From Calorie Restriction?
Calorie restriction is a type of dietary restriction that refers to a prolonged reduction in average calorie intake without causing malnutrition8. There are positive health benefits associated with calorie restriction, including an improvement in insulin sensitivity, reduced inflammation, and a reduction in adipose (fat) tissue.
The CALERIE trial has shown that prolonged moderate caloric restriction improves cardio-metabolic risk factors, such as high blood pressure and insulin sensitivity9. Furthermore, researchers have found that caloric restriction may reduce the risk of cancer10. That said, calorie restriction is difficult to maintain, thus leading to a growing interest in fasting, particularly intermittent fasting.
What Are the Benefits of Fasting?
Obesity and overnutrition are major risk factors for an array of diseases that pose a significant burden on the health of our population. There’s increasing evidence that various types of fasting can help protect against numerous diseases and slow down the ageing process11.
Here are some potential benefits
of fasting:
- Promotes weight loss and reduces body fat.
- Lowers cardiovascular risk factors, such as reducing blood pressure and improving lipid profile12.
- Reduces insulin levels and improves insulin sensitivity and β-cell responsiveness13.
- Reduces chronic inflammation14.
- Helps cell maintenance, cell survival, and the removal of cellular waste products by inducing a process known as autophagy15.
- Activates stem cells, which play a role in immune system regeneration16.
Even if you don’t want to try fasting, you can adopt lifestyle changes to improve your heart health.
Fasting and Cancer: Understanding the Connection
Fasting may have indirect and direct roles in cancer prevention. For starters, fasting can promote weight loss, encourage broader positive lifestyle changes, and inspire healthier eating habits, thus reducing the risk of obesity.
Since obesity is a risk factor for many types of cancer, including bowel cancer, breast cancer, prostate cancer, ovarian cancer, and pancreatic cancer, fasting can have an indirect role in cancer prevention17.
Additionally, identifying and promoting ways to reduce the incidence of obesity is pivotal, as cancer patients with obesity have been shown to have poorer outcomes18. Obesity has been linked to a higher incidence of recurrence, disease progression, and mortality19. The molecular mechanisms are complex, but chronic inflammation, insulin resistance, and dysregulation of sex hormones offer possible explanations.
Does Fasting Affect Tumor Development?
The question that many researchers have been trying to answer is whether fasting can directly affect tumour development and growth. Fasting has been thought to cause anticancer effects by inducing conditions that limit cancer cells’ ability to adapt, survive, and grow.
There have been several proposed mechanisms, one of which involves insulin-like growth factor-1 (IGF-1). Higher levels of IGF-1 are associated with certain types of cancer, such as breast cancer, colon cancer, and prostate cancer20. It has been shown to cause inhibition of apoptosis (programmed cell death), as well as causing genomic instability and promoting cells to proliferate21.
Evading apoptosis is one of the ways in which cancer cells can grow and divide. Fasting methods have been shown to reduce levels of IGF-1. Intermittent fasting has been shown to reduce the rate of both T-cell and B-cell acute lymphoblastic leukaemia, the molecular mechanism of which is thought to involve a reduction in insulin and IGF-122.
Additionally, the hormonal changes and metabolic effects associated with fasting (such as increased insulin sensitivity) have been shown to reduce oxidative stress, promote stress resistance, reduce inflammation, and promote DNA repair, which are important in mitigating tumour growth23.
That said, evidence on the direct effect of fasting on cancer prevention is inconsistent24. Early rodent studies have shown that intermittent fasting fails to stop tumour growth. However, a clinical trial found that 13-hour fasting at night resulted in a lower risk of breast cancer recurrence25.
Further research is required to validate the findings and help us understand intermittent fasting and its clinical application in oncology and cancer prevention.
Does Fasting Play a Role in Cancer Treatment?
As we know, anticancer treatments like chemotherapy and radiation can be very toxic, causing serious side effects for cancer patients. This has led to a huge advancement in the development of targeted anticancer therapies that act on specific receptors, reducing the exposure of normal cells to toxic drugs.
There’s a growing body of evidence that short-term fasting can sensitise cancer cells to the effects of chemo regimens and protect normal cells, which can reduce toxic side effects26. A mechanism known as “differential stress resistance” is believed to play a role, which results in the protection of normal cells and promotes the death of cancer cells27.
A randomised clinical trial looking at the effects of a fasting-mimicking diet in addition to pre-surgery chemotherapy in breast cancer patients found no difference in toxicity, but it significantly reduced chemotherapy-induced DNA damage in normal cells28.
However, a recent systematic review and meta-analysis concluded that there is not sufficient evidence to demonstrate the effect of fasting in reducing the side effects of chemo29. Further studies are required and would be safer performed in patients with types of cancer, such as breast cancer, ovarian cancer, or prostate cancer, in which the patients are most likely to experience weight gain.
It’s important to note that intermittent fasting, FMD, or calorie restriction is not appropriate for everyone. Cancer patients are at particular risk of malnutrition. If you’re being treated for cancer and are considering fasting, be sure to consult your oncologist before doing so.
Fasting and FMD: Are There Risks?
As with many interventions, there are risks and potential side effects. Fasting can cause symptoms such as severe hunger, nausea, headaches, light-headedness, irritability, and fatigue. It can lead to an increase in cortisol, a stress hormone, in times of severe hunger.
Fasting also increases the risk of dehydration, as our food provides a source of fluid. As such, it’s essential to maintain adequate fluid intake during fasting periods. Finally, fasting can result in symptoms of acid reflux, such as a burning sensation in your stomach. Easing into a fasting regimen will help reduce the risk of these side effects. Be sure to consult your doctor if you are concerned.
Fasting should not be attempted by everyone, particularly those who are:
- At risk of malnutrition, have a low body weight, or struggle to gain weight
- Older in age and at risk of losing too much weight
- Have a history of an eating disorder or are at risk of an eating disorder
- Pregnant or breastfeeding
- Taking medications that may cause electrolyte imbalances
- Have diabetes
Everyone has varying nutritional needs and metabolic demands. Be sure to tailor your diet in a way that works for you. If you’re considering intermittent fasting, caloric restriction, or a fasting-mimicking diet, speak to a nutritionist or doctor before commencing.
Fasting and Cancer: Moving Forward
Fasting has been shown to provide many health benefits. However, its direct role in cancer prevention and treatment remains unclear. There’s certainly some promising evidence to suggest that fasting and cancer have a positive connection, but larger randomised studies are required to provide conclusive evidence.
The bottom line is that no diet has been shown to prevent cancer. One of the most important actions you can take is to eat a healthy, balanced diet and undertake regular physical activity to reduce your risk of obesity.
Another important step you can take is to attend your local Ezra location for an MRI Scan with Spine. Ezra screens for up to 500+ potential conditions to give you peace of mind over your health. Be proactive about your health and join today.
Understand your risk for cancer with our 5 minute quiz.
Our scan is designed to detect potential cancer early.
References
1. Cancer mortality for common cancers. Cancer Research UK. May 13, 2015. Accessed November 5, 2025. https://www.cancerresearchuk.org/health-professional/cancer-statistics/mortality/common-cancers-compared
2. Cancer risk statistics. Cancer Research UK. May 13, 2015. Accessed November 5, 2025. https://www.cancerresearchuk.org/health-professional/cancer-statistics/risk
3. UK cancer statistics. World Cancer Research Fund. Accessed November 5, 2025. https://www.wcrf.org/preventing-cancer/cancer-statistics/uk-cancer-statistics/
4. Fasting | Definition, Description, Types, Benefits, & Facts | Britannica. October 18, 2025. Accessed November 5, 2025. https://www.britannica.com/topic/fasting
5. Chen YE, Tsai HL, Tu YK, Chen LW. Effects of different types of intermittent fasting on metabolic outcomes: an umbrella review and network meta-analysis. BMC Med. 2024;22:529. doi:10.1186/s12916-024-03716-1
6. Herz D, Karl S, Weiß J, et al. Effects of Different Types of Intermittent Fasting Interventions on Metabolic Health in Healthy Individuals (EDIF): A Randomised Trial with a Controlled-Run in Phase. Nutrients. 2024;16(8):1114. doi:10.3390/nu16081114
7. Wei M, Brandhorst S, Shelehchi M, et al. Fasting-mimicking diet and markers/risk factors for aging, diabetes, cancer, and cardiovascular disease. Sci Transl Med. 2017;9(377):eaai8700. doi:10.1126/scitranslmed.aai8700
8. Spadaro O, Youm Y, Shchukina I, et al. Caloric restriction in humans reveals immunometabolic regulators of health span. Science. 2022;375(6581):671-677. doi:10.1126/science.abg7292
9. Kraus WE, Bhapkar M, Huffman KM, Pieper CF, Das SK, Redman LM. 2 years of calorie restriction and cardiometabolic risk (CALERIE): exploratory outcomes of a multicentre, phase 2, randomised controlled trial. The Lancet Diabetes & Endocrinology. 2019;7(9):673-683. doi:10.1016/S2213-8587(19)30151-2
10. Vidoni C, Ferraresi A, Esposito A, et al. Calorie Restriction for Cancer Prevention and Therapy: Mechanisms, Expectations, and Efficacy. J Cancer Prev. 2021;26(4):224-236. doi:10.15430/JCP.2021.26.4.224
11. Tang D, Tang Q, Huang W, Zhang Y, Tian Y, Fu X. Fasting: From Physiology to Pathology. Advanced Science. 2023;10(9). doi:10.1002/advs.202204487
12. Hailu KT, Salib K, Savithri Nandeesha S, et al. The Effect of Fasting on Cardiovascular Diseases: A Systematic Review. Cureus. 16(1):e53221. doi:10.7759/cureus.53221
13. Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even Without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212-1221.e3. doi:10.1016/j.cmet.2018.04.010
14. Aamir AB, Kumari R, Latif R, et al. Effects of intermittent fasting and caloric restriction on inflammatory biomarkers in individuals with obesity/overweight: A systematic review and meta-analysis of randomized controlled trials. Obes Rev. 2025;26(1):e13838. doi:10.1111/obr.13838
15. Bagherniya M, Butler AE, Barreto GE, Sahebkar A. The effect of fasting or calorie restriction on autophagy induction: A review of the literature. Ageing Res Rev. 2018;47:183-197. doi:10.1016/j.arr.2018.08.004
16. Abdel Hadi L, Sheikh S, Suarez-Formigo GM, et al. Intermittent Fasting During Ramadan Increases the Absolute Number of Circulating Progenitor Stem Cells in Healthy Subjects. Stem Cells Dev. 2025;34(1-2):35-47. doi:10.1089/scd.2024.0194
17. Pati S, Irfan W, Jameel A, Ahmed S, Shahid RK. Obesity and Cancer: A Current Overview of Epidemiology, Pathogenesis, Outcomes, and Management. Cancers (Basel). 2023;15(2):485. doi:10.3390/cancers15020485
18. Clifton KK, Ma CX, Fontana L, Peterson LL. Intermittent fasting in the prevention and treatment of cancer. CA: A Cancer Journal for Clinicians. 2021;71(6):527-546. doi:10.3322/caac.21694
19. Obesity and Cancer Fact Sheet - NCI. April 13, 2022. Accessed November 6, 2025. https://www.cancer.gov/about-cancer/causes-prevention/risk/obesity/obesity-fact-sheet
20. Mukama T, Srour B, Johnson T, Katzke V, Kaaks R. IGF-1 and Risk of Morbidity and Mortality From Cancer, Cardiovascular Diseases, and All Causes in EPIC-Heidelberg. J Clin Endocrinol Metab. 2023;108(10):e1092-e1105. doi:10.1210/clinem/dgad212
21. Adamson L, Walum E. Insulin and IGF-1 mediated inhibition of apoptosis in CHO cells grown in suspension in a protein-free medium. Altern Lab Anim. 2007;35(3):349-352. doi:10.1177/026119290703500301
22. Boogaard WM van den, Heuvel-Eibrink MM van den, Hoeijmakers JH, Vermeij WP. Nutritional Preconditioning in Cancer Treatment in Relation to DNA Damage and Aging. Annual review of cancer biology. 2020;5:161. doi:10.1146/annurev-cancerbio-060820-090737
23. FINK J, TANAKA M, HORIE S. Effects of Fasting on Metabolic Hormones and Functions: A Narrative Review. Juntendo Iji Zasshi. 2024;70(5):348-359. doi:10.14789/jmj.JMJ24-0012-R
24. Tiwari S, Sapkota N, Han Z. Effect of fasting on cancer: A narrative review of scientific evidence. Cancer Sci. 2022;113(10):3291-3302. doi:10.1111/cas.15492
25. Marinac CR, Nelson SH, Breen CI, et al. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncol. 2016;2(8):1049-1055. doi:10.1001/jamaoncol.2016.0164
26. de Groot S, Pijl H, van der Hoeven JJM, Kroep JR. Effects of short-term fasting on cancer treatment. Journal of Experimental & Clinical Cancer Research. 2019;38(209). doi:10.1186/s13046-019-1189-9
27. Raffaghello L, Lee C, Safdie FM, et al. Starvation-dependent differential stress resistance protects normal but not cancer cells against high-dose chemotherapy. Proc Natl Acad Sci U S A. 2008;105(24):8215-8220. doi:10.1073/pnas.0708100105
28. de Groot S, Lugtenberg RT, Cohen D, et al. Fasting mimicking diet as an adjunct to neoadjuvant chemotherapy for breast cancer in the multicentre randomized phase 2 DIRECT trial. Nat Commun. 2020;11(1):3083. doi:10.1038/s41467-020-16138-3
29. Ferro Y, Maurotti S, Tarsitano MG, et al. Therapeutic Fasting in Reducing Chemotherapy Side Effects in Cancer Patients: A Systematic Review and Meta-Analysis. Nutrients. 2023;15(12):2666. doi:10.3390/nu15122666
