Fasting, according to a recent study from the Icahn School of Medicine at Mount Sinai, may make it more difficult to fight infections and increase your risk of developing heart disease. The study, which used mouse models, is one of the first to show that skipping meals causes the brain to react in a way that damages immune cells. The findings, which focus on breakfast, were published in the journal Immunity and may help researchers better understand how long-term fasting affects the body.
“There is a growing awareness that fasting is healthy, and there is indeed abundant evidence for the benefits of fasting. Our study provides a word of caution as it suggests that there may also be a cost to fasting that carries a health risk,” said lead author Filip Swirski, PhD, Director of the Cardiovascular Research Institute at Icahn Mount Sinai, adding, “This is a mechanistic study delving into some of the fundamental biology relevant to fasting. The study shows that there is a conversation between the nervous and immune systems.”
Researchers wanted to learn more about how fasting affects the immune system, from a short fast of a few hours to a longer fast of 24 hours. They looked at two groups of mice. The first group ate breakfast immediately after waking up (breakfast is their largest meal of the day), while the second group did not. Blood samples were taken from both groups of mice when they awoke (baseline), four hours later, and eight hours later.
When researchers examined the blood work, they noticed a distinct difference in the fasting group. The researchers noticed a difference in the number of monocytes, which are white blood cells that are produced in the bone marrow and travel throughout the body, where they play a variety of important roles ranging from fighting infections to heart disease to cancer.
All mice had the same number of monocytes at the start. Monocytes in mice from the fasting group, on the other hand, were significantly affected after four hours. Researchers discovered that 90% of these cells vanished from the bloodstream after eight hours, and the number continued to decline. Monocytes in the non-fasting group, on the other hand, were unaffected.
Researchers discovered that in fasting mice, monocytes returned to the bone marrow to hibernate. Concurrently, the bone marrow’s ability to produce new cells decreased. Monocytes in the bone marrow, which have a short lifespan, changed dramatically. They lived longer because they remained in the bone marrow and aged differently than monocytes that remained in the blood.
The researchers fasted the mice for up to 24 hours before reintroducing food. Within a few hours, the cells that had been hiding in the bone marrow were released into the bloodstream. This surge resulted in increased inflammation. Instead of protecting the body from infection, these altered monocytes were more inflammatory, making it less resistant to infection.
This is one of the first studies to establish a link between the brain and these immune cells while fasting. The researchers discovered that specific brain regions controlled the monocyte response during fasting. Fasting causes a stress response in the brain, which is what causes people to feel “hangry” (hungry and angry), and this immediately causes a large-scale migration of these white blood cells from the blood to the bone marrow, and then back to the bloodstream shortly after food is reintroduced.
While there is evidence of the metabolic benefits of fasting, Dr. Swirski emphasises that this new study is a useful advance in the full understanding of the body’s mechanisms.
“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 into the blood, which can be problematic. Fasting, therefore regulates this pool in ways that are not always beneficial to the body’s capacity to respond to a challenge such as an infection,” said Dr. Swirski, adding, “Because these cells are so important to other diseases like heart disease or cancer, understanding how their function is controlled is critical.”