New research from The University of Manchester is changing the way scientists think about how fasting affects the immune system.
In a study on mice, researchers discovered that the brain—not just the absence of food—plays a central role in how the body’s immune system responds when we don’t eat.
The study, published in Science Immunology, focuses on the hypothalamus, a small but powerful part of the brain that helps control hunger. The researchers found that a few special neurons in the hypothalamus, which are responsible for creating the feeling of hunger, can influence immune cells throughout the body.
What’s especially surprising is that it’s not necessary for an animal to actually fast in order to trigger changes in the immune system. Simply making the brain think the body is hungry is enough.
To test this, scientists used a method to artificially activate hunger-related neurons in mice. These neurons typically switch on when the body’s energy levels are low. When the researchers turned these neurons on, the mice didn’t eat less—but their brains believed they were hungry.
Within just a few hours, the scientists saw significant changes in the mice’s immune systems, particularly a drop in inflammatory monocytes, a type of immune cell involved in inflammation.
These changes were very similar to what happens when mice fast for real. In other words, even though these mice hadn’t skipped any meals, their immune systems responded as if they had.
This finding is important because it challenges the long-held belief that the immune system responds to fasting simply because the body is running low on nutrients. Instead, the brain’s signals about hunger may be the main driver of these changes.
Dr. Giuseppe D’Agostino, who led the research, explained that our bodies don’t just respond to the actual presence or absence of food, but also to how the brain perceives hunger. He said, “It’s easy to see how thoughts guide our actions, but this study reminds us that even our internal body adjustments that are not under conscious control respond to the brain’s signals.”
The researchers believe these findings could have a wide range of health implications. For example, this new understanding might help develop better treatments for inflammatory diseases like arthritis, as well as conditions like cancer-related wasting, where patients lose weight and muscle even though they’re eating.
It may also help explain why people with obesity often suffer from inflammation, and why undernourished people are more likely to get infections.
Professor Matt Hepworth, a co-author of the study, said this research shows that the nervous system plays a powerful role in how the immune system behaves during fasting. “This work challenges the long-standing view that fasting’s immunological impact is driven purely by nutrient levels,” he said.
Dr. Cavalcanti de Albuquerque, the study’s lead author, added that understanding how the brain controls the immune system gives scientists a new way to explore how fasting can benefit health. It also opens doors to future treatments for infections, inflammation, metabolic problems, and even mental health conditions.
In short, this study reveals a fascinating link between the mind and the body. It shows that the brain’s perception of hunger—not just actual fasting—can quickly reorganize the immune system. This insight highlights how deeply connected our brains and immune systems are, and suggests new ways to promote health by working with the brain’s natural signals.
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The research findings can be found in Science Immunology.
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