A recent study by the Icahn School of Medicine at Mount Sinai reveals that fasting could be detrimental to fighting off infections and increases the risk of heart disease. The research focused on mouse models. The results, published in the February 23 issue of Immunity, indicate that skipping meals can trigger a response in the brain that negatively affects immune cells. This is one of the first studies to explore how chronic fasting might affect the body in the long term.

The study aimed to better understand how fasting affects the immune system, from a relatively short fast of only a few hours to a more severe fast of 24 hours. Researchers analyzed two groups of mice, one of which ate breakfast right after waking up, and the other group had no breakfast. Researchers collected blood samples from both groups when mice woke up, then four and eight hours later.

The researchers observed a difference in the number of monocytes in the fasting group, which are white blood cells made in the bone marrow and play a crucial role in fighting infections, heart disease, and cancer. After four hours, monocytes in mice from the fasting group were significantly affected, and 90% of these cells disappeared from the bloodstream. In contrast, monocytes in the non-fasting group were unaffected.

The researchers discovered that the monocytes in the fasting mice traveled back to the bone marrow to hibernate, significantly changing their lifespan and aging process. The study found that instead of protecting against infection, these altered monocytes were more inflammatory and made the body less resistant to fighting infection.

The study demonstrated that fasting elicits a stress response in the brain, which instantly triggers a large-scale migration of white blood cells from the blood to the bone marrow and then back to the bloodstream shortly after food is reintroduced. Researchers found that specific regions in the brain controlled the monocyte response during fasting.

While the study provides a word of caution, there is abundant evidence for the benefits of fasting, including the metabolic benefits. Understanding how fasting regulates immune cells is critical, as these cells are essential components of inflammation and vital to other diseases like heart disease or cancer.