Fasting can help kill cancer. It reprograms the immune system’s “natural killer” (NK) cells to combat cancer’s spread, and it also starves
cancer cells of the nutrients they need to grow. NK cells are a type of white blood cell that can kill abnormal or damaged cells, such as cancer cells or cells infected by a virus. Unlike T cells, they can ward off a threat even if they have never
encountered it before. Researchers at Memorial Sloan Kettering Cancer Center have discovered in lab tests on mice how fasting kick-starts the NK cells into action.
Fasting for 24 hours twice a week—and then eating normally the rest of the time—reduces glucose (sugar) levels and increases free fatty acids, which are lipids released by fat cells that act as an alternative energy source. This change also occurs in humans.
During the fasting periods, the NK cells learned to use the fatty acids as fuel, which “optimizes their anticancer response,” explained Rebecca Delconte, one of the researchers. They haven’t tested this action in humans yet, but they’ve observed that fasting changes the way NK cells circulate in humans.

The two 24-hour weekly fasts didn’t have any detrimental effect, and there was no weight loss, the researchers added. In the next phase of the study, the researchers will test different types of fasting to see which ones are the most effective.