The link between fasting and cancer continues to be a topic of mass discussion, but does fasting really have an impact in 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 United States. Some of these deaths could be avoidable, with many cancers linked to modifiable risk factors.
According to the American Society of Cancer, at least 42% of new cancer cases in 2023 were potentially avoidable, with 18% attributable to alcohol, excess body weight, low levels of physical activity, and poor nutritional status. 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.
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 practiced 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 illness.
There are three main types of fasting: intermittent fasting, time-restricted feeding, and prolonged fasting. Let’s take a closer look at each one.
Intermittent fasting involves fasting cycles, which relates 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% of normal calorie intake for two non-consecutive days and normal calorie consumption for the remaining five days.
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 hours. There is no calorie restriction.
This refers to fasting periods lasting more than 24 hours.
A fasting-mimicking diet (FMD) is slightly different than 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 randomized clinical trial carried out by Professor Longo indicated that FMD reduces risk factors and markers associated with aging and disease, although larger studies are required to confirm the findings.
Calorie restriction is a type of dietary restriction that refers to a prolonged reduction in average calorie intake without causing malnutrition. 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 sensitivity. Furthermore, the American Cancer Society has found that caloric restriction may reduce the risk of cancer (and explains the underlying molecular mechanisms involved). That said, calorie restriction is difficult to maintain, thus leading to a growing interest in fasting, particularly intermittent 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 aging process.
Here are some potential effects of fasting:
Even if you don’t want to try fasting, you can adopt lifestyle changes to improve your heart health.
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 prevention.
Additionally, identifying and promoting ways to reduce the incidence of obesity is pivotal as cancer patients with obesity have been shown to have poorer outcomes. Obesity has been linked to a higher incidence of recurrence, disease progression and mortality. The molecular mechanisms are complex, but chronic inflammation, insulin resistance, and dysregulation of sex hormones offer possible explanations.
The question that many researchers have been trying to answer is whether fasting can directly affect tumor 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 IGF-1. Higher levels of IGF-1 are associated with certain types of cancer such as breast cancer, colon cancer, and prostate cancer. It has been shown to cause inhibition of apoptosis (programmed cell death), as well as causing genomic instability and promoting cells to proliferate.
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. Per the previously mentioned report by the American Cancer Study, intermittent fasting has been shown to reduce the rate of both T-cell and B-cell acute lymphoblastic leukemia, the molecular mechanism of which is thought to involve a reduction in insulin and IGF-1.
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 tumor growth.
That said, evidence on the direct effect of fasting in cancer prevention is inconsistent. Early rodent studies have shown that intermittent fasting fails to stop tumor growth. However, a clinical trial in humans found that 13-hour fasting at night resulted in a lower risk of breast cancer recurrence.
Further research is required to validate the findings and help us understand intermittent fasting and its clinical application in oncology and cancer prevention.
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 sensitize cancer cells to the effects of chemo regimens and protect normal cells, which can reduce toxic side effects. 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 cells.
After positive results in yeast and mice, there have been a few small clinical trials published that indicate that short-term fasting is well-tolerated in different types of cancer and reduces side effects and toxicity to anticancer therapy.
A randomized 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 cells.
However, a recent systematic review and meta-analysis concluded that there’s not sufficient evidence to demonstrate the effect of fasting in reducing the side effects of chemo. 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 prior to doing so.
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:
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 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 randomized 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. Other important steps are getting cancer screening tests such as the Ezra Full Body Scan to detect cancer early. As the American Cancer Society has stated, early detection saves lives.