Mount Sinai Research Finds Skipping Breakfast May Compromise the Immune System
By THE MOUNT SINAI HOSPITAL / MOUNT SINAI SCHOOL OF MEDICINE
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| The image shows that during fasting a specific region in the brain controls redistribution of monocytes in the blood with consequences on response to infection upon refeeding. Credit: Mount Sinai Health System |
A recent study from the Icahn
School of Medicine at Mount Sinai suggests that fasting could negatively affect
immune cells, potentially increasing the risk of infection and heart disease.
Fasting may be detrimental to fighting off infection, and could lead to an increased risk of heart disease, according to a new study by the Icahn School of Medicine at Mount Sinai. The research, which focused on mouse models, is among the first to show that skipping meals triggers a response in the brain that negatively affects immune cells.
The results that focus on breakfast were recently
published in the journal Immunity, and
could lead to a better understanding of how chronic fasting may affect the body
long term.
“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,” says lead author Filip Swirski, PhD, Director of the Cardiovascular Research Institute at Icahn Mount Sinai.
“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 aimed to better understand how fasting — from a relatively short fast of only a few hours to a more severe fast of 24 hours — affects the immune system. They analyzed two groups of mice. One group ate breakfast right after waking up (breakfast is their largest meal of the day), and the other group had no breakfast. Researchers collected blood samples in both groups when mice woke up (baseline), then four hours later, and eight hours later.
When examining the blood work,
researchers noticed a distinct difference in the fasting group.
Specifically, the researchers saw a difference in the number of monocytes,
which are white blood cells that are made in the bone marrow and travel through
the body, where they play many critical roles, from fighting infections, to
heart disease, to cancer.
At baseline, all mice had the
same amount of monocytes. But after four hours, monocytes in mice from the
fasting group were dramatically affected. Researchers found 90 percent of these
cells disappeared from the bloodstream, and the number further declined at
eight hours. Meanwhile, monocytes in the non-fasting group were unaffected.
In fasting mice, researchers
discovered the monocytes traveled back to the bone marrow to hibernate.
Concurrently, production of new cells in the bone marrow diminished. The
monocytes in the bone marrow—which typically have a short
lifespan—significantly changed. They survived longer as a consequence of staying
in the bone marrow, and aged differently than the monocytes that stayed in the
blood.
The researchers continued to
fast mice for up to 24 hours, and then reintroduced food. The cells hiding in
the bone marrow surged back into the bloodstream within a few hours. This surge
led to a heightened level of inflammation. Instead of protecting against
infection, these altered monocytes were more inflammatory, making the body less
resistant to fighting infection.
This study is among the first
to make the connection between the brain and these immune cells during fasting.
Researchers found that specific regions in the brain controlled the monocyte
response during fasting. This study demonstrated that fasting elicits a stress
response in the brain—that’s what makes people “hangry” (feeling hungry and
angry) —and this instantly triggers 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.
Dr. Swirski emphasized that while
there is also evidence of the metabolic benefits of fasting, 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, reintroduction of food creates a surge of monocytes flooding
back to 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,” explains Dr. Swirski. “Because these
cells are so important to other diseases like heart disease or cancer,
understanding how their function is controlled is critical.”
Reference: “Monocytes re-enter
the bone marrow during fasting and alter the host response to infection” by
Henrike Janssen, Florian Kahles, Dan Liu, Jeffrey Downey, Laura L. Koekkoek,
Vladimir Roudko, Darwin D’Souza, Cameron S. McAlpine, Lennard Halle, Wolfram C.
Poller, Christopher T. Chan, Shun He, John E. Mindur, Máté G. Kiss, Sumnima
Singh, Atsushi Anzai, Yoshiko Iwamoto, Rainer H. Kohler, Kashish Chetal, Ruslan
I. Sadreyev, Ralph Weissleder, Seunghee Kim-Schulze, Miriam Merad, Matthias
Nahrendorf and Filip K. Swirski, 23 February 2023, Immunity.
DOI: 10.1016/j.immuni.2023.01.024
