BOSTON (WHN) – For millennia, fasting has been observed as a natural response to illness, a phenomenon now being investigated for its potential role in cancer treatment and prevention.
Researchers are exploring how short-term periods of caloric restriction might bolster the immune system’s ability to target cancer cells, while simultaneously offering protection to healthy tissues during conventional therapies like chemotherapy.
Historically, physicians noted that sick individuals often lose their appetite. This reduced food intake, far from being just an undesirable symptom, appears to be an active defense mechanism. While chronic undernutrition can weaken the body, short-term food deprivation, data suggest, can actually enhance immune function.
Experiments in mice demonstrated a striking effect: blood from starved animals was nearly eight times more effective at killing invading bacteria in laboratory settings, significantly boosting the pathogen-killing capacity of their white blood cells.
The question then arises: does this translate to humans, and specifically to cancer?
A study involving human participants who fasted for two weeks on an extremely low-calorie diet (80 calories per day) yielded intriguing results. Their white blood cells exhibited a similar boost in bacteria-killing ability and antibody production. Notably, natural killer cell activity increased by an average of 24%.
Natural killer cells are critical components of the immune system, not only clearing infections but also identifying and destroying cancer cells. Researchers assessed this activity by pitting these cells against K562 cells, a type of human leukemia cell.
Fasting is theorized to improve “anticancer immunosurveillance,” a concept sometimes described as “stimulating the appetite of the immune system for cancer.” Yet, fasting isn’t widely adopted in cancer care. This is largely due to a historical focus on maintaining patient weight to combat cancer cachexia, a syndrome of severe weight loss and muscle wasting that is a common and often fatal consequence of the disease.
Tumors are metabolically demanding, requiring significant energy and protein. They can reprogram the body to break down its own tissues to fuel this growth, often by triggering systemic inflammation. This process goes beyond mere appetite loss; the weight loss seen in cancer cachexia is fundamentally different from simple starvation because, as researchers have noted, it often proves irreversible with feeding alone.
Nutritional interventions aimed at correcting cachexia frequently fall short. The most effective strategy for cancer cachexia, therefore, remains treating the underlying cancer. The notion that aggressively feeding cancer patients might inadvertently support tumor growth is gaining traction, akin to how a fetus prioritizes nutrients during pregnancy.
For decades, chemotherapy has been a cornerstone of cancer treatment, primarily targeting cancer cells by inducing DNA damage, partly through the production of free radicals. While initially thought to be highly selective for tumors, it became clear that normal cells also suffer significant damage from these treatments. This leads to dose-limiting side effects, including bone marrow suppression, immune system compromise, fatigue, and gastrointestinal issues.
The DNA damage to healthy cells from chemotherapy can even increase the risk of secondary cancers later in life. While protective drugs exist to mitigate side effects, allowing for higher chemotherapy doses, they haven’t consistently shown an increase in survival, potentially because they may also shield cancer cells.
This has spurred interest in fasting as a means of cellular protection during cancer treatment.
The potential role of fasting in cancer prevention and treatment is becoming clearer. Short-term fasting periods, implemented before and after chemotherapy, may help minimize treatment side effects and, theoretically, make cancer cells more vulnerable to therapy.
During periods of deprivation, healthy cells can shift from growth to maintenance and repair. Tumor cells, however, often cannot slow their rapid proliferation due to mutations that drive their unbridled growth. This inability to adapt to starvation could represent a critical vulnerability for many cancer types.
The differential response to short-term fasting suggests that chemotherapy might inflict more DNA damage and cell death in tumor cells, while sparing healthy cells. This mechanism, at least in theory, could protect normal tissues from the toxic effects of chemotherapy and enhance its efficacy against tumors.
In animal studies, fasting alone has shown efficacy comparable to chemotherapy in some instances. Tumor growth was also reduced by radiation therapy, and even more so when combined with alternate-day fasting. Intriguingly, alternate-day fasting alone appeared to be as effective as radiation in rodent models of breast cancer.
Human data, however, are more complex. Several patients with various cancers who voluntarily undertook fasting before chemotherapy reported reduced fatigue, weakness, and gastrointestinal side effects, experiencing no vomiting and recovering lost weight quickly without discernible harm. These anecdotal reports suggest that fasting, when supervised, may be safe and help alleviate treatment side effects.
A randomized clinical trial involving breast and ovarian cancer patients who fasted for 36 hours before and 24 hours after chemotherapy did appear to improve quality of life and reduce fatigue. However, another study found no such benefits. Some evidence pointed to potentially reduced bone marrow toxicity, indicated by higher red blood cell and platelet counts, but no significant benefit was observed in preserving white blood cells.
A systematic review of 22 studies indicated that fasting might not only reduce chemotherapy side effects but also suppress tumor progression, including growth and metastasis, potentially leading to improved survival. Critically, nearly all these studies were conducted in rodents and canines. Human studies have largely focused on safety and side effects, with the impact of fasting on tumor growth, metastasis, and prognosis remaining unevaluated.
Short-term food withdrawal during chemotherapy could address a long-standing challenge: how to eliminate tumors without harming the patient. Fasting, for example, for 48 hours before and 24 hours after chemotherapy, may mitigate treatment-induced toxicity. Yet, the potential tumor-suppressing effects of fasting require further thorough investigation.
Some experts propose that reducing chemotherapy’s side effects alone could enhance its efficacy, as patients might tolerate higher doses. For instance, damage to the heart and kidneys from certain widely used anti-cancer drugs limits their therapeutic potential. It remains unclear, however, if maximizing tolerated chemotherapy doses would translate to longer survival or improved quality of life. For now, mitigating side effects for their own sake may be a reasonable objective.
Fasting has been shown to lower levels of insulin-like growth factor-1 (IGF-1), a hormone that promotes cancer growth. Reduced IGF-1 signaling is believed to mediate the differential protection of normal versus cancer cells during fasting and enhance chemotherapy’s ability to kill tumors while sparing healthy tissues.
Therefore, reducing IGF-1 signaling may offer dual benefits: protecting normal tissues and hindering tumor progression. It might even play a role in cancer prevention. While a few days of fasting can halve IGF-1 levels, this is largely due to reduced protein intake. Protein intake is a key determinant of circulating IGF-1, suggesting that “reduced protein intake may become an important component of anticancer and antiaging dietary interventions,” particularly a reduction in animal protein consumption.
Comparing individuals who adhere to plant-based diets with recommended protein intake (0.8 grams per kg of body weight) to leaner individuals consuming higher protein amounts typical in the American diet, calorie restriction may offer modest reductions in IGF-1. However, a plant-based diet appears to lower IGF-1 levels more substantially than low-calorie diets alone.
Consequently, a diet centered on whole plant foods may not only down-regulate IGF-1 activity, potentially slowing the aging process, but could also harness anti-aging mechanisms against cancer.