Fasting plus vitamin C effective for hard-to-treat cancers, study says

A fasting-mimicking diet could be more effective at treating some types of cancer when combined with vitamin C, according to a new study by researchers at the University of Southern California in Los Angeles and published in the journal Nature Communications.

In studies on mice, researchers led by Valter Longo, PhD, director of the University of Southern California Longevity Institute and professor at the University of Southern California Leonard Davis School of Gerontology, found that the combination delayed tumor progression in multiple mouse models of colorectal cancer; in some mice, it caused disease regression.

The researchers said that while fasting remains a challenging option for cancer patients, a safer, more feasible option is a low-calorie, plant-based diet that causes cells to respond as if the body were fasting. Their findings suggest that a low-toxicity treatment of fasting-mimicking diet plus vitamin C has the potential to replace more toxic treatments.

Results of prior research on the cancer-fighting potential of vitamin C have been mixed. Recent studies, though, are beginning to show some efficacy, especially in combination with chemotherapy. In this new study, the research team wanted to find out whether a fasting-mimicking diet could enhance the high-dose vitamin C tumor-fighting action by creating an environment that would be unsustainable for cancer cells but still safe for normal cells.

Longo and his colleagues detected this strong effect only in cancer cells that had a mutation that is regarded as one of the most challenging targets in cancer research. These mutations in the KRAS gene signal the body is resisting most cancer-fighting treatments, and they reduce a patient's survival rate. KRAS mutations occur in approximately a quarter of all human cancers and are estimated to occur in up to half of all colorectal cancers.

The study also provided clues about why previous studies of vitamin C as a potential anticancer therapy showed limited efficacy. By itself, a vitamin C treatment appears to trigger the KRAS-mutated cells to protect cancer cells by increasing levels of ferritin, a protein that binds iron. By reducing levels of ferritin, the scientists managed to increase vitamin C toxicity for the cancer cells. Amid this finding, the scientists also discovered that colorectal cancer patients with high levels of the iron-binding protein have a lower chance of survival, according to the study.

The research team's prior studies showed that fasting and a fasting-mimicking diet slow cancer's progression and make chemotherapy more effective in tumor cells, while protecting normal cells from chemotherapy-associated side effects. The combination enhances the immune system's anti-tumor response in breast cancer and melanoma mouse models, the researchers said.

The scientists said they believe cancer will eventually be treated with low-toxicity drugs in a manner similar to how antibiotics are used to treat infections that kill particular bacteria, but which can be substituted by other drugs if the first is not effective.

To move toward that goal, they said they needed to first test two hypotheses, that their non-toxic combination interventions would work in mice, and that it would look promising for human clinical trials. In this new study, they said that they've demonstrated both. At least five clinical trials are now investigating the effects of the fasting-mimicking diets in combination with different cancer-fighting drugs.

"For the first time, we have demonstrated how a completely non-toxic intervention can effectively treat an aggressive cancer," said Longo in a statement. “We have taken two treatments that are studied extensively as interventions to delay aging, a fasting-mimicking diet and vitamin C, and combined them as a powerful treatment for cancer."