Intermittent Fasting and Cancer
Over the past decade, there has been increased scientific interest in fasting and its relationship to chronic diseases, including cancer. There is emerging evidence that intermittent fasting has positive effects on metabolism, decreases cellular growth signaling pathways and reduces inflammation in the body. Different protocols for intermittent fasting have been developed, and it is still not clear which populations would benefit most from fasting, how long to fast, or how frequently. However, as the research continues to expand, many of those questions will likely be answered. Here's what we know now.
Some patients report decreased side effects when they fast around chemotherapy infusions. Several small clinical trials have found that patients with a variety of cancer types experience fewer chemotherapy-related side-effects from fasting for several days before, during and/or after chemotherapy infusions. In addition, preliminary research demonstrates that fasting during treatment can improve prognosis. Intermittent fasting is also known as time-restricted feeding and there are three main types:
- Alternate day fasting where you fast every other day
- 5:2 fasting where you eat normally for five days and then choose two days to restrict calories typically to about 500 per day
- Overnight fasting shortens the eating window to about ten hours which means there is a 14 hour overnight fast
There is some evidence that overnight fasting might reduce cancer recurrence rates in people with a history of breast cancer. Over 2000 patients with a history of breast cancer were followed for 11 years to evaluate their risk of breast cancer recurrence. Women who routinely fasted overnight for 13 hours or more had a reduced risk of breast cancer recurrence. For example, stopping eating or drinking (anything other than water or black tea or coffee) at 7 pm and not eating or drinking again until 8 am the next morning would be a 13 hour overnight fast.
A clear protocol for how to fast, or for how long, has not been defined. In general, one to three days of fasting around chemotherapy should only be attempted if you are not at risk of losing weight, not underweight, not at risk of malnutrition or protein deficiency, are not elderly, are not taking medications for diabetes, and if your chemotherapy infusions are spaced out at least 3 weeks apart. Ideally, it is best to discuss the risks and benefits of fasting and chemotherapy with a trusted health care provider or registered oncology dietician who knows your medical history and is well-versed in the different types of fasts.
