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Fasting as a cancer treatment

To Eat or Not to Eat: With Cancer Therapies, That Is the Question
The following is from the website of the National Cancer Institute

What we eat and when we eat it can affect the way the body absorbs and reacts to cancer treatments.

Dr. Longo and oncologists from USC published a study of 10 elderly cancer patients who voluntarily underwent short-term fasting before and/or after cytotoxic chemotherapy infusion. Patients reported fewer side effects, including fatigue, weakness, and gastrointestinal problems, when they fasted. However, some doctors still worried that fasting could also protect cancer cells, explained Dr. Longo, which would negate its use in cancer patients.

A study by the USC research team, published in Science Translational Medicine, addressed this concern by showing that, contrary to such fears, fasting renders cancer cells more sensitive to chemotherapy.

Fasting also deprives cancer cells of the glucose and other molecules they need to fuel their endless cell division. Therefore, fasting adds a second stressor on top of chemotherapy, forcing cancer cells to deal “with two extreme environments at once,” explained Dr. Longo.

Overnight Fasting (13 hours)

In this study, data were collected from 2413 women with breast cancer but without diabetes mellitus who were aged 27 to 70 years at diagnosis and participated in the prospective Women’s Healthy Eating and Living study.

Findings: nightly fasting less than 13 hours was associated with a statistically significant 36% increased risk of breast cancer recurrence compared with nightly fasting more than 13 hours or more. Nightly fasting less than 13 hours was not associated with a statistically significant higher risk of breast cancer mortality or a statistically significant higher risk of all-cause mortality

The authors hypothesized that interventions to prolong the nightly fasting interval could potentially reduce the risk of type 2 diabetes, cardiovascular disease, and other cancers.

Short-term Fasting (24-hour)

Short-term fasting is a type of fast during which you cannot consume anything besides water. Most water fasts last 24–72 hours. You should not follow a water fast for longer than this without medical supervision.

This study concluded:
Abundant and convincing preclinical evidence shows that STF [short-term fasting] can decrease toxicity and simultaneously increase efficacy of a wide variety of chemotherapeutic agents. Preclinical data suggesting that STF can enhance the effects of radiotherapy and TKIs [tyrosine kinase inhibitors] are promising as well. In clinical studies, STF emerges as a promising strategy to enhance the efficacy and tolerability of chemotherapy. It appears safe as an adjunct to chemotherapy in humans, and it may reduce side effects and DNA damage in healthy cells in response to chemotherapy.

Intermittent Fasting

Intermittent Fasting typically takes two forms:

  1. Time Restricted Eating. This involves eating within an 8 to 10-hour window during a 24-hour period. For example, on the 16/8 diet you would eat during an 8-hour period and fast for the other16 hours.
  2. Alternate Day Fasting (with or without purposeful caloric restriction). This comprises an alternating pattern between non-restricted days and fasted days with no caloric intake. However, in real world conditions these are poorly tolerated and have recently been replaced with modified Alternate Day Fasting protocols, which allow for an intake of up to 40% of the recommended daily caloric intake on fasted days. Source

In this study of 2413 women with breast cancer, a short nightly fasting duration of less than13 hours per night was associated with a 36% higher hazard for breast cancer recurrence compared with fasting 13 or more hours per night. Conclusions: Prolonging the length of the nightly fasting interval may be a simple, nonpharmacologic strategy for reducing the risk of breast cancer recurrence.

The Fasting Mimicking Diet (FMD) is a program that aims to mimic the effects of fasting while still allowing some food intake. The FMD involves consuming a low-calorie, low-protein, and low-carbohydrate diet for 4–7 days.

This study randomised 131 patients with HER2-negative stageII/III breast cancer, without diabetes and a BMI over 18 kg m−2, to receive either a fasting mimicking diet (FMD) or their regular diet for 3 days prior to and during neoadjuvant chemotherapy.

This study says: The results suggest that an FMD significantly reinforces the effects of neoadjuvant chemotherapy on the radiological and pathological tumor response in patients with HER2negative early breast cancer. The ITT analysis reveals an increase of patients with a radiologically complete or partial response and a reduction of patients with radiologically stable/progressing disease in the FMD group compared to the control group.

This study says:
It is important to consider that FMDs will not be effective in reducing the side effects of cancer treatments in all patients and neither will they work to improve the efficacy of all therapies, but they have great potential to do so at least for a portion and possibly for a major portion of patients and drugs. Frail or malnourished patients or patients at risk of malnutrition should not be enrolled in clinical studies of fasting or FMDs, and patient nutritional status and anorexia should be carefully monitored throughout clinical trials. An appropriate intake of proteins, essential fatty acids, vitamins and minerals combined, where possible, with light and/or moderate physical activity aimed at increasing muscle mass should be applied between fasting or FMD cycles in order for the patients to maintain a healthy lean body mass. This multimodal dietary approach will maximize the benefits of fasting or FMDs while at the same time protecting patients from malnutrition.

This 2020 study says:
In the past years, the dynamic role of autophagy has gained increasing attention as it could be a therapeutic target for several diseases, including cancer.

The preponderance of evidence indicated that autophagy suppresses tumorigenesis and inhibits cancer cell adaptation, proliferation, survival, and invasion or metastasis.

The National Cancer Institute definition of autophagy is as follows:
A process by which a cell breaks down and destroys old, damaged, or abnormal proteins and other substances in its cytoplasm (the fluid inside a cell). The breakdown products are then recycled for important cell functions, especially during periods of stress or starvation. Autophagy also helps destroy bacteria and viruses that cause infection and may prevent normal cells from becoming cancer cells. Once cancer has formed, autophagy may protect the cancer cells by providing extra nutrients to them or by keeping anticancer drugs or other substances from destroying them. Autophagy may also affect the body’s immune response against viruses, bacteria, and cancer cells.

Prolonged fast (5-50 days)

A prolonged fast is an extended period, typically over 36 hours without eating. During this time, water, electrolytes and noncaloric beverages are allowed.

In Effect of fasting on cancer: A narrative review of scientific evidence the authors say:

Emerging evidence suggests that fasting could play a key role in cancer treatment by fostering conditions that limit cancer cells’ adaptability, survival, and growth. Fasting could increase the effectiveness of cancer treatments and limit adverse events…We recommend combining prolonged periodic fasting with a standard conventional therapeutic approach to promote cancer‐free survival, treatment efficacy and reduce side effects in cancer patients.

This study, published in the British Medical Journal says: We report the case of a 42-year-old woman diagnosed by excisional biopsy with stage IIIa, grade 1 FL [Follicular lymphoma]. In addition to close observation, the patient underwent a medically supervised, 21-day water-only fast after which enlarged lymph nodes were substantially reduced in size. The patient then consumed a diet of minimally processed plant foods free of added sugar, oil and salt (SOS), and has remained on the diet since leaving the residential facility. At 6 and 9-month follow up visits, the patient’s lymph nodes were non-palpable and she remained asymptomatic.

(Follicular lymphoma (FL) is an incurable, indolent form of non-Hodgkin’s lymphoma.)


Source: The UCSF Osher Center for Integrative Medicine
In a large cohort study of 2000 participants, fasting (350 kcal/day) was shown to be safe and actually beneficial to their chronic disease (rheumatic diseases, chronic pain syndrome, hypertension, metabolic syndrome). The biggest concern with calorie restriction and fasting as it relates to cancer is weight loss. As discussed above, weight loss is actually less of a concern with short-term fasting than it is with long-term calorie restriction. For people who are overweight, this can be a positive side effect; however, for cancer patients who are already underweight or struggling to maintain their weight, additional weight loss may be detrimental and be a contraindication to fasting or CR [calorie restriction]. It is also worth mentioning that side effects, such as headache, light-headedness, nausea, or weakness, can occur when fasting longer than several days. Side effects, such as anemia or amenorrhea, can occur with fasting lasting several weeks.  The longer the fast, the more important it is to take care in re-feeding.  This phase needs to be gradual and incremental in order to prevent severe problems–or even death–coming off of a prolonged fast.

What is Our Recommendation?
Comparing the research between CR and fasting, fasting seems to provide more dramatic results and protection of healthy cells, without the risk of weight loss or immune suppression. Both CR and fasting are the subject of ongoing research, and definitive conclusions await the results of those studies. As mentioned above, it may not be appropriate for everyone, particularly those who are underweight or very ill, and should never be attempted without the supervision of qualified practitioners.

This 2020 study says:
Overall, data on fasting are in favour of the safety and feasibility of these approach, with some authors suggesting an improvement even of QoL and fatigue in patients under chemotherapy, especially in the 8 days after chemotherapy treatment. Conversely, data about survival outcomes are still controversial, but it should be underlined that it was not the outcome of these preliminary studies. In synthesis, all the prospective studies about fasting found that it is able to reduce chemotherapy toxicity and, at the same time, to increase quality of life in patients receiving these approach. At the same time, all studies are concordant about safeness ad feasibility of fasting (according the schemes pro in patients receiving chemotherapy.

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