While there is research indicating that fasting has numerous benefits, such as improving conditions like obesity, diabetes, and even neurological disorders, there is still debate around whether these benefits outweigh the potential negative side effects. Now, a new study from the Mount Sinai School of Medicine has shown that fasting may compromise the immune system and increase the risk of heart disease, adding to the body of literature that demonstrates fasting may not be a net positive practice.
Using mice, the research team focused on how skipping breakfast can manifest health risks. They analyzed blood samples drawn from two groups of mice at three different periods in the fasting period: immediately upon waking up, four hours after waking up, and eight hours after waking up. One group ate breakfast immediately after waking up while the other group was given no breakfast. Upon examining the blood samples, the researchers found that mice in the fasting group had far fewer monocytes (white blood cells that combat infection) in the bloodstream—90 percent of the monocytes were absent from the bloodstream after four hours, and that figure dropped even further after another four hours. Meanwhile, the group that had breakfast had a consistent number of monocytes throughout the entire period.
The researchers found that the monocytes in fasting mice migrated back to the bone marrow to “hibernate,” while cell production in the bone marrow slowed. Finally, the monocytes in the bone marrow had longer lifespans than the typical monocyte because the marrow is a “safe haven for monocytes during nutrient scarcity.”
After 24 hours, the fasting group was fed once more, prompting the dormant monocytes in the bone marrow to surge back into the bloodstream. The rapid distribution of monocytes caused inflammation, undermining the body’s immune response.
In the experiment, the researchers discovered that certain brain regions regulated monocyte behavior during the fasting period. Fasting elicits a stress response in the brain, which in turn triggers the monocytes to migrate back into the bone marrow and then, after eating, flood the bloodstream again. This study is one of the first to indicate a connection between the nervous system and immune system.
One of the study authors, Filip Swirski, PhD, director of the Cardiovascular Research Institute, indicated that more research is needed to know the full effects of fasting on the body’s various systems. “The study shows that, on the one hand, fasting reduces the number of circulating monocytes, which one might think is a good thing as these cells are important components of inflammation. On the other hand, [the] reintroduction of food creates a surge of monocytes flooding back to the blood, which can be problematic,” he said. “Because these cells are so important to other diseases like heart disease or cancer, understanding how their function is controlled is critical.”