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Fasting has long been a part of human tradition, practiced across many civilizations and religions as an important ritual or spiritual discipline. It’s often associated with devotion, purification, and self‑discipline.
When we think of fasting, the first thing that may come to mind is Ramadan, the holy month observed by Muslims as one of the five pillars of Islam. Ramadan involves fasting from dawn (Fajr) to sunset (Maghrib) each day for a full month. It is observed as an exercise of devotion to willingly renounce oneself from all bodily appetites while also avoiding unsocial or negative behaviors. Instead, participants focus on improving social conduct by engaging in acts of charity, helping the poor, elderly, and needy. The fasting period is meant to foster discipline for the body and the soul, encouraging self-control and ethical behavior that continues after the month ends.
It is permissible for individuals who are traveling, on sick leave, or working outdoors in harsh climate conditions, or for pregnant women, to refrain from fasting if their health condition does not permit it.
It is believed that the body is detoxified from all sorts of toxins during this month – but only if healthy habits are maintained. This includes eating nutritious, vitamin-rich foods and staying active with regular exercise. Running a marathon might be unfeasible but going for a long walk every day supports fasting. Good sleep is a big part of fasting – being an early riser and starting the day shortly before dawn with a nutritious pre-dawn meal and going to bed early to give the body enough sleep time to re‑energize.
In addition to religious practices, fasting has gained popularity as a health and wellness practice in recent years. A growing body of research has explored the effects of fasting on various diseases, including neurological diseases. It has been suggested as a mood enhancer in chronic pain syndrome or as an adjunct therapy during chemotherapy for cancer. However, more research is needed in these areas to fully understand the potential benefits and risks of fasting for these conditions.
Medical professionals have highlighted the many health benefits of fasting, saying for example: “Fasting can bring plenty of benefits to your health. It encourages weight loss, stimulates fat burning, improves metabolism, promotes cellular renewal and rejuvenation (autophagy), enhances insulin sensitivity, and much more.”1
Nevertheless, what is often reported throughout studies is that individual responses vary and depend on various factors, such as diet, sleeping habits, exercise, fluid intake, and fasting regimen.
The length of fasting can vary depending on individual preferences, goals, and achievements. Let us go through the main practices, which are not limited to the list below:
This method consists of alternating between periods of eating and fasting, which may suit busy individuals. The basic idea is to fast for one day with a strict calorie intake; on eating days, a regular diet is allowed.
In ADF, fasting days where calorie intake is strictly limited, alternate with eating days, where a regular diet is allowed.
This involves eating within a specific time window. The most popular method is 16:8, where you fast for 16 hours and have an eating window of eight hours.
This approach focuses on the calorie intake of each meal, making it an easier form of fasting to follow. It typically involves consuming 40% and less of your usual calorie intake for a certain number of days.
You might encounter other variations of fasting called “juice fasting”, “water fasting” or “protein fasting”, etc.
Multiple applications and special programs have emerged as a result of an increasing global desire for healthier and longer lives. It is essential, while considering the plethora of offers, for individuals to proceed with caution and ideally consult a professional to avoid any irreversible health consequences.
It’s difficult to delve into the effects of fasting therapy on each disease in this article, but we have highlighted the diseases that are within the scope of studies that show positive predictions for the future.
The beneficial claims of fasting are supported by experimental research, which has found fasting to be associated with increased brain availability of serotonin, endogenous opioids, and endocannabinoids.2 Fasting-induced neuroendocrine activation and mild cellular stress response with increased production of neurotrophic factors may also contribute to the mood enhancement effects of fasting.3 Fasting as a supplementary treatment for chronic pain, particularly in conditions such as rheumatoid arthritis, is gaining attention.
The mood-enhancing and pain-relieving effect of therapeutic fasting has been evaluated in randomized clinical trials. Many observational studies or clinical trials have been performed.4
In one trial, all patients received acupuncture treatments, hydrotherapy,5 practiced various mind-body approaches,6 and attended classes on nutrition and lifestyle habits. They were also offered the chance to participate in a modified seven-day fast. The consumption of two liters of liquid per day (including mineral water, fruit juice, tea, and vegetable broth) provided a certain number of calories. Upon discharge from hospital, fasting patients reported a significantly greater decrease in their main symptoms than other patients, with no serious side effects reported.
Various studies have shown that changes in diet can have a positive effect on the symptoms of patients with rheumatoid arthritis. A 2001 review including four controlled studies, with a total of 143 subjects, evaluated the effect of fasting for seven to 23 days followed by a vegetarian diet. The study led to long-term improvements in the fasting groups such as reduction in pain and increase in functional capacity.8
Research has explored medically supervised fasting as a treatment for hypertension. In most cases, the patients consumed only fruits and vegetables for two to three days, and then only water for the next 10 to 11 days.
They completed the program with a six to seven-day vegetarian diet. A part of the sample patients in some trials had high blood pressure and were not taking medication. The rest of the sample had only borderline high blood pressure. The results of the two studies indicate a statistically significant decrease in blood pressure after the fasting.9 Additionally, almost 90% of subjects in the first study and ca. 80% of those in the second study had normal blood pressure readings at the end of the intervention.10
Clinical data on fasting in cancer patients are rare. The review of various studies and research outcomes in this article aims at summarizing published clinical data on fasting and its effects on patients undergoing chemotherapy. Therefore, it gives some direction in advising patients with the desire to fast and provides insights for healthcare providers considering fasting as an adjunct to treatment.
Chemotherapy is the primary treatment for most cancers. However, a large number of cancer patients who undergo chemotherapy experience mild to severe side-effects.11 The major chemotherapy-related side-effects include nausea, vomiting, weakness, fatigue, loss of appetite, gastrointestinal symptoms, pain, and hematologic toxicity, which severely impact patients’ quality of life.
Despite advancements, inadequately controlled vomiting and nausea remain major problems in many patients who then delay or discontinue oncological treatments and consequently increase their mortality risk. Therefore, in addition to improving survival rates, the development of non-toxic therapies in the cancer care setting is essential. A variety of fasting regimens seem to be capable of preventing the undesirable effects of chemotherapy.
Italian, French, American and German medical researchers have been working on such clinical trials for the past decade.
Emerging evidence suggests that fasting could play a vital role in cancer treatment by creating conditions that hinder the ability of cancer cells to adapt, survive, and grow. Fasting may also enhance the effectiveness of cancer treatments and mitigate harmful factors.
However, a comprehensive mechanistic understanding of the interplay between fasting and cancer therapy is still lacking. This review explores recent findings at the intersection of oncology and fasting metabolism, focusing on human clinical studies related to intermittent fasting. Researchers often suggest combining prolonged periodic fasting with conventional cancer treatments to improve survival rates, enhance treatment effectiveness, and reduce chemotherapy side‑effects.12
One of the notable studies reviewed involved cancer patients diagnosed with breast and gynecological cancers. Fasting duration and timepoints ranged significantly (24 to 140 hours before, and on the day of chemotherapy to 56 hours after chemotherapy). In one study patients were fasting before cancer surgery. The studies were mostly low to moderate quality and reported heterogeneous results. The overall conclusion was that fasting for short periods does not have any beneficial effect on the quality of life of cancer patients during treatment.13
A more recent study focusing on early-stage breast cancer patients provided promising results.14 The research, titled “Effects of Short-Term Fasting on Quality of Life as an Add‑On Option During Chemotherapy”, was presented at the European Society for Medical Oncology (ESMO) Congress in October 2023. The German study, conducted by Charité Universitätsmedizin Berlin, included 106 women aged 29 to 71, all diagnosed with early-stage breast cancer. The cohort was split into two groups: one followed a short-term fasting regimen, while the other adhered to a plant-based diet.
Among the test group 18.2% were diagnosed with hormone receptor-negative breast cancer and 81.8% were diagnosed with hormone receptor-positive breast cancer. All the women received chemotherapy: 15.4% received four cycles of Adriamycin (chemical name: doxorubicin) or Ellence (chemical name: epirubicin) every three weeks, followed by four cycles of a taxane, such as Taxol (chemical name: paclitaxel). 84.6% received four cycles of Adriamycin or Ellence every three weeks, followed by 12 cycles of a taxane; 45.3% received chemotherapy before breast cancer surgery; 54.7% received chemotherapy after surgery and short-term fasting or plant-based diet.
The researchers advised both groups to eat a more vegetable-based diet overall, but this wasn’t required.
The women were randomly split into two groups, a short-term fasting group and a plant-based diet group. The short-term fasting group included 52 women: for 36 to 48 hours before chemotherapy and for 24 hours after chemotherapy, they ate about 200 calories a day, in the form of vegetable juices and vegetable broths. The plant-based diet group, in contrast, avoided refined carbohydrates, high-sugar foods, and proteins during the same periods.
Measuring quality of life and fatigue, the researchers used a standard survey called the Functional Assessment of Cancer Therapy-General (FACT‑G), to assess the women’s quality of life. The survey asked about physical, social, emotional, and functional wellbeing. To measure fatigue, the researchers used another standard survey called the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT).
One of the most notable findings was the impact of fasting on fatigue: both groups had similar scores on the FACT‑G survey, meaning quality of life was roughly the same among participants. After the fourth cycle of chemotherapy, the short-term fasting group’s average score on the FACT‑G survey was nine points higher than that of the plant-based diet group. This difference was statistically significant, which means that it was probably because of the difference in diet and not due to chance.
“What was even more striking was the impact fasting had on fatigue,” said presenter Daniela Koppold, MD, of Charité University Medicine in Berlin, Germany. “The short-term fasting group didn’t develop any clinically visible fatigue. They were in a normal range for fatigue by cycle four of chemotherapy, while the plant-based diet group developed fatigue as we would have expected.”
Dr. Koppold also noted that fasting didn’t affect the women’s weight, which was important because losing too much weight during chemotherapy can cause more side-effects and interfere with the medicines’ effectiveness. She pointed out that women who were underweight or who had a history of an eating disorder were excluded from the study.
There were no differences in scores for anxiety and depression between the two groups, suggesting that the difference in quality of life wasn’t based on those factors. “In summary, short-term fasting represents a promising supportive therapy during breast cancer chemotherapy to enhance quality of life,” Dr. Koppold said.
The studies conducted thus far indicate promising effects in the treatment of cancer patients by reducing the side-effects of intensive treatments such as chemotherapy, and also positive effects in treatment of various other diseases. Further larger and randomized studies are needed at this point to confirm these findings and to support the reported positive effects. With more positive study results regarding different disease, fasting therapies under medical guidance may be able to cast a positive light on underwriting specific diseases in the future.
All endnotes last accessed 14 February 2025.
