If you’re generally healthy and you ask your doctor about which trendy eating style is best for you, from vegan, to paleo, to gluten-free, they’ll probably tell you to do whatever encourages you to eat the most wholesome foods in reasonable amounts. On the other hand, research over the past several decades has also shown that diet plays a role in the prevention of diseases like cancer, so those who have a family history or are generally trying to preserve their health are also often interested in the best disease-fighting diets out there. Enter: fasting. While not eating is generally considered an unhealthy thing to do, there’s evidence fasting might help prevent and stop the progression of cancer, especially intermittent fasting, which is also sometimes used as a weight-loss strategy.
Fasting and Cancer Theory
You might be wondering where the idea that fasting can cure cancer came from, and it's actually not a new theory. “Fasting as a way to slow cancer cells has been looked at for over 100 years,” says Shikha Jain, MD, a hematology oncology physician. “It has been known for some time that cancer cells use a different pathway for obtaining energy than regular cells,” adds Javier Roca, MD, a board-certified oncologist/hematologist at Queens Medical Associates. “Metabolic pathways for obtaining energy change in fasting conditions, and this may be exploitable to specifically target cancer cells.” In other words, changing cancer cells’ access to “fuel” by restricting calories might help to slow their growth.
Before you start thinking of fasting as a miracle cure, Jain notes that it’s important to keep in mind that most relevant studies have been done on animals and have not been able to be replicated consistently in people. That being said, there is some limited evidence that certain types of fasting may have a positive effect. Many types of fasting have been studied, from completely refraining from food for prolonged periods of time to only eating a certain number of calories per day or restricting food intake to a certain number of hours per day.
One such study found that women who went longer periods between their last meal of the day and their first meal of the next day may have been at a lower risk for breast cancer. “We know that there is a connection between obesity and some cancers,” explains Dorothy D. Sears, Ph.D., who worked on the study and is an associate professor at the University of California San Diego School of Medicine. “We also know that physical activity and diet can reduce your risk of some cancers. So we decided to look at not just what you eat but when you eat. Evidence that intermittent fasting improves obesity-related blood glucose control and inflammation in mouse models is very strong. These same metabolic pathways are involved in cancer cell growth.”
In basic terms, that means that while it’s not a sure thing, there is some evidence that intermittent fasting might be useful for cancer prevention. “We have also found in women who prolonged nightly fasting and ate fewer calories at nighttime were associated with reduced inflammation, another mechanism that could impact breast cancer risk,” she says.
Fasting During Treatment
There’s also some buzz about using fasting not just as a means of cancer prevention, but in conjunction with traditional cancer treatment. While there is some evidence that it could be helpful, it also comes along with some risks. “Fasting during chemotherapy can be dangerous in some cases,” Jain says. “By not getting the proper nutrition, not maintaining one’s weight, and not taking in enough protein, patients who are already weak from cancer and chemotherapy can become weaker.” People who are fasting may also experience the side effects of chemotherapy more intensely. For this reason, “the majority of oncologists will likely be against a complete fasting plan, especially in patients who need to maintain their weight and their overall fitness level in order to continue to safely receive chemotherapy,” Jain explains.
It’s crucial to keep your oncologist (and ideally a nutritionist) informed of any dietary changes you make or intend to make during treatment.
The Bottom Line
The takeaway here? “The evidence supporting fasting regimens is still in its infancy,” Jain says. For those who are dealing with cancer, “whether or not it’s safe to try is highly dependent on each patient’s condition and the physician’s judgment.” For those who are concerned with prevention, it probably doesn’t hurt to eat less at night, but it’s not something that is going to guarantee you never get cancer. And if you’re looking to make a change to the way you eat for cancer prevention, Jain has some advice: “I typically recommend people eat less processed food, less red meat, and more fruits and vegetables, as opposed to fasting.” Just make sure you talk to a health practitioner before making any drastic diet changes.