Fasting, or not eating food for an extended period of time, is well-known as a religious diet practice. But some are also beginning to use it for specific health benefits. Over the past several years, many studies have been published showing that intermittent fasting or a fasting-mimicking diet can reduce risk factors for and reverse symptoms of serious health conditions including cancer.
Intermittent fasting is fasting on a schedule, alternated with times of eating. For example, you may eat normally for most of the week, but on Tuesdays and Thursdays only eat for an 8-hour period and fast for the remaining 16 hours. Some also call this a fasting-mimicking diet.
Although it seems unusual in modern society where food is abundant, the human body is built to accommodate times when food sources are scarce. In history, fasting has often been necessary in the face of famine or other natural disasters that limit food supply.
Your body is designed to protect you against starvation. To do this, it stores a reserve of the nutrients needed to survive when you eat.
When you’re not eating normally, this puts the cells under mild stress, and your body begins to release those stores to fuel itself. Doctors suggest that as long as your body has time to heal itself after this period of stress, you won’t experience negative effects.
It’s important to be careful about fasting for an extended period of time that your body cannot handle. Complete or continuous fasting will trigger “starvation mode,” in which your body starts slowing down to prolong your life. This typically begins after three days of continuous fasting. During this fasting period of more than three days, your body will hold on to fuel stores as much as possible, and you won’t notice weight loss.
Weight loss is just one benefit of intermittent fasting for a normal healthy (disease-free) adult. Recent animal studies and a few preliminary human trials have shown a decrease in risk for cancer or a decrease in cancer growth rates. These studies indicate this may be due to the following effects from fasting:
- decreased blood glucose production
- stem cells triggered to regenerate the immune system
- balanced nutritional intake
- increased production of tumor-killing cells
In one study of time-restricted feeding during 9–12 hour phases, fasting was shown to reverse the progression of obesity and type 2 diabetes in mice. Obesity is a major risk factor for cancer, which may support fasting to treat cancer.
A second study of mice showed that a bimonthly fasting-mimicking diet reduced the incidence of cancer. Results were similar in a pilot trial by the same scientists with 19 humans; it showed decreased biomarkers and risk factors for cancer.
In a 2016 study, research showed that a combination of fasting and chemotherapy slowed the progression of breast cancer and skin cancer. The combined treatment methods caused the body to produce higher levels of common lymphoid progenitor cells (CLPs) and tumor-infiltrating lymphocytes. CLPs are the precursor cells to lymphocytes, which are white blood cells that migrate into a tumor and are known for killing tumors.
The same study noted short-term starvation makes cancer cells sensitive to chemotherapy while protecting normal cells, and it also promoted the production of stem cells.