To fast or not to fast


To humbly paraphrase Shakespeare, the question is “whether ‘tis better to…ban sugar from your diet, or bulk up on high-protein meals…” The internet is full of raging debates, fervid testimonials and opinions about what you should or shouldn’t eat when you’re being treated for cancer.

 One of the most common chat topics is whether you should cut out ‘sugar’ to decrease the amount of “fuel” available for voracious cancer cells.

If only cancer, and nutrition, were so simple. But every kind of calorie is fuel, every cell uses fuel, and cells become cancerous in many different ways.  

But thankfully, scientists are working hard to shed more light (than heat) on the role that nutrients might play in cancer cells—and they’re coming up with some tantalizing clues, according to the most recent National Cancer Institute Cancer Bulletin (July 10 2012).

For example, researchers are asking, if cancer patients went on a total food fast before and/or after chemotherapy sessions, could that reduce side effects or even make the treatments more effective in destroying cancer cells?

Dr. Valter Longo, professor of gerontology and biology at the University of Southern California (USC), has been peering into the actual cells—both normal and cancer—in both tissue cultures and in mice to see how normal and cancer cells respond to fasting, and to chemotherapy drugs after fasting for 2 or 3 days before treatment.

His laboratory has found that fasting causes dramatic—and very different–changes in the cells. Normal cells essentially go into a “survival mode,” turning down their genes that stimulate cell growth to target what little energy they have into a protective, maintenance and cell-repair mode. Theoretically, this might make normal cells less harmed by chemotherapy.

In contrast, cancer cells seem to have mutations that prevent them from shifting into this slow-growth protective mode, so they’re actually more sensitive to chemotherapy–especially drugs that target fast-growing cells, according to a study the USC team published in the March 2012 Science Translational Medicine. The cancer cells also get a double-whammy because the fasting deprives them of the fuel they need as they keep trying to grow and divide quickly.

Other trials have shown that tumors in fasting mice grew slower, and much slower in mice that fasted before getting an anticancer drug. But there’s been only one tiny study in humans: In 2009, ten elderly human volunteers with a variety of cancerswere able to fast safely from 2 to 5 days before, and up to 2 days after, chemotherapy treatments. In cycles when they fasted, they reported fewer side effects from chemotherapy.

Dr. Longo and others have started three early-phase human trials, with another two multi-center trials to begin shortly. The human trials will test whether fasting is safe, whether it might reduce chemotherapy side effects, and how—or if—it changes how well different cancer drugs work against tumors and cancer cells.

IMPORTANT: Fasting may well be dangerous with oral chemotherapy

The NCI Bulletin article also reported why fasting should not be tried with oral drugs taken as pills. Certain oral cancer drugs (such as nilotinib for leukemia and lapatinib for breast cancer) are strongly affected by being taken with or without food. Some drugs don’t work as well, some oral drugs are vastly strengthened by the presence or absence of food in the gut when these medicines are taken. University of Chicago researchers are now studying whether fasting could be safe, or how it would change necessary doses for certain drugs.

PATIENT TAKE-AWAY: Don’t try this at home. 

If you are taking any oral cancer medicine, don’t fast. Period. You could suffer a life-threatening overdose, or you could unintentionally weaken your chemotherapy so that it doesn’t work.

 Even if you’re on intravenous chemotherapy, remember that there are no human trial results yet. You wouldn’t want to make yourself an “experiment of one” without careful discussion with your cancer team. It’s not just your specific cancer, but also your overall condition and organ functions (like kidneys) that would be affected by fasting. Whether you benefit or could get seriously weakened by fasting needs thorough consideration: At the very least, print out the NCI Bulletin and take it to discuss with your oncologist.

And stay tuned: we’ll report on research results as they come in, here at Research News.

Sources:  NCI Cancer Bulletin, July 10 2012, Vol. 9, No 14: “To Eat or Not to Eat: With Cancer Therapies, That Is the Question”; and Aging, Dec. 2009 Vol.1 No 12, “Fasting and Cancer Treatment in Humans: A Case series report.”



  1. Jennifer says

    Thank you for this informative piece on an issue of interest to everyone on chemo.

    I think it would also be useful to provide the reference and link to the piece you cite as appearing in the “March 2012 Science Translational Medicine. “

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