Fasting may compromise the immune system

March 09, 2023 | Biology

Abundant evidence has shown metabolic benefits of fasting. However, a new mechanistic study conducted on mouse models from the Icahn School of Medicine at Mount Sinai, provided a word of caution that skipping meals might pose detrimental health risks that could lead to heart disease. They exhibited the fundamental biology relevant to fasting and how it triggers a response in the brain that negatively impacts immune cells.

The researchers particularly looked at how chronic fasting can affect the immune system long term. They tested two groups of mice: one group ate breakfast while the other did not. They collected blood samples in both groups every time they woke up (baseline), four hours later, and then eight hours.

Through blood work, the researchers recognized a difference in the number of monocytes in the fasting group. From baseline up until eight hours later, monocytes in the fasting group dramatically dropped, with 90% disappearing from the bloodstream as they hibernated back to the bone marrow. As a consequence, there is a decrease in production of new cells. These monocytes also have a longer lifespan compared to the monocytes that stayed in the blood. When food is reintroduced after fasting the mice for 24 hours, the altered cells rush back to the bloodstream with heightened levels of inflammation. This made the body less resistant to fighting off infection.

Furthermore, as the brain releases a stress response during fasting, much of these monocytes will travel from the blood to hibernate in the bone marrow, and back to blood once food is reintroduced. However, they are already altered and inflamed.

Thus, fasting modulates the pool of white blood cells in ways that are not always helpful to the body’s capacity to respond to infection. Understanding how these cells function and what controls them is critical.