Periodic fasting may protect immune system health among healthy middle-aged people and the elderly, along with chemotherapy patients and other people who suffer immune-related conditions, a new study finds.

As our bodies age or are exposed to various forms of stress, such as disease and autoimmune disorders, the white blood cells that once conquered harmful invaders now, unfortunately, relent. In their weakened state, they allow the body’s immune health to suffer, putting people at risk for earlier death. In fact, among cancer-related deaths, it’s estimated that roughly one-fifth are hastened, or even caused, by toxicities related to chemotherapy, and not the actual cancer itself.

The new study, conducted by researchers from the University of Southern California, revealed that temporary nutrient restriction could protect the body’s immune cells. At first, they found, the initial starvation actually causes the body’s white blood cell count to drop. But once feeding resumes, the count bounces back to even greater numbers than before.

"We discovered that this effect, which may have evolved to reduce energy expenditure during periods of starvation, is able to switch stem cells to a mode able to not only regenerate immune cells and reverse the immunosuppression caused by chemotherapy, but also rejuvenate the immune system of old mice,” said senior researcher Dr. Valter Longo in a statement. Longo and his colleagues also found that 72-hour fasting periods resulted in less white blood cell loss among chemotherapy patients.

Basically, when people undergo a fast — in the study’s case, for two to four days every six months — their bodies rely on current energy stores to keep the body healthy. In drawing from these stores, the body will use up old immune cells that, as Longo tells the Daily Mail, “are not needed, especially those that may be damaged.”

“With a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system,” Longo added.

Additional experiments showed that fasting raised the levels of insulin-like growth factor-1 (IGF-1) — a protein that, because of its roles in regulating aging and growth, can similarly help chemotherapy patients, the elderly, and those with immunodeficiency disorders. Other treatments that do not rely on fasting, but still target the IGF-1 pathways, may also prove beneficial.

Chemotherapy is regularly criticized for its invasiveness and high risk of collateral damage. The popular cancer treatment relies on killing cells that rapidly divide — a hallmark of cancer cells. But not all rapidly dividing cells are cancerous, which means a person’s normal, healthy cells get caught in the crossfire. This explains why cancer patients undergoing chemo see a decrease in their immune health, experience digestive issues, and lose their hair.

Longo, for his part, is confident the team will find follow-up successes in diets that replicate the effects of fasting. "We and others are currently testing the effect of fasting-mimicking diets on the protection of patients against chemotherapy's side effects,” Longo said, “and we're also testing the role of multiple cycles of a fasting-mimicking diet on the immune system in generally healthy middle-aged and elderly subjects.”

Source: Cheng C, Adams G, Perin L, et al. Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression. Cell Stem Cell. 2014.