Does Intermittent Fasting Improve Immunity? The Science Behind Its Effects

November 30, 2025 •

4 min read

Research indicates that fasting strategies may benefit immune health by modulating immune responses and suppressing inflammation. This growing body of evidence has led many to wonder: does intermittent fasting improve immunity, and what biological processes are involved in this complex relationship?

Quick Summary

Intermittent fasting influences the immune system through various mechanisms, including regulating inflammation, promoting cellular repair via autophagy, and altering the gut microbiome. While studies suggest potential long-term benefits like rejuvenation, temporary immune cell shifts can also occur, making individual health context important.

Key Points

Immune Regeneration: Fasting promotes autophagy, a cellular repair process that removes old, damaged cells and regenerates new, healthier ones, potentially rejuvenating the immune system.
Inflammation Reduction: By shifting metabolism and producing anti-inflammatory ketones like β-hydroxybutyrate (BHB), intermittent fasting helps lower chronic inflammation markers in the body.
Improved Gut Health: Fasting can alter the gut microbiome, promoting beneficial bacteria that produce immune-supportive compounds like short-chain fatty acids (SCFAs), which reduce inflammation.
Metabolic Flexibility: The switch from glucose-based metabolism to fat-based metabolism during fasting enhances metabolic flexibility, making cells more resilient to stress and illness.
Consideration of Risks: While beneficial, fasting may cause temporary immune suppression or a transient increase in inflammation for some individuals, especially during prolonged fasts.
Long-term vs. Short-term Effects: Long-term, consistent intermittent fasting is associated with greater benefits, while short-term effects include temporary shifts in immune cell populations.

The immune system is a complex network of cells and organs that defend the body against pathogens. Intermittent fasting (IF), an eating pattern that cycles between periods of eating and fasting, has gained popularity for its potential health benefits. Emerging research suggests a significant connection between IF and immune function, primarily driven by metabolic adaptations and cellular renewal processes. Understanding how intermittent fasting improves immunity involves looking at several key biological pathways that are activated during periods of caloric restriction.

Key Mechanisms: How Fasting Modulates the Immune System

Cellular Recycling via Autophagy

One of the most potent effects of fasting is the activation of autophagy, a cellular "housecleaning" process where the body removes and recycles old, damaged, and redundant cells. During fasting, nutrient deprivation signals cells to shift from growth to repair mode, triggering autophagy. In the immune system, this process can eliminate defective immune cells and clear pathogens from within cells, leading to a population of fresh, more effective cells upon refeeding. This rejuvenation can enhance the body's ability to combat infections and reduce age-related decline of the immune system.

Anti-Inflammatory Effects

Chronic, low-grade inflammation is a significant driver of many age-related diseases, including type 2 diabetes and cardiovascular disease. A high-calorie, Western-style diet can promote systemic inflammation. Intermittent fasting can help break this cycle. Studies show that fasting can lead to a decrease in pro-inflammatory cytokines, such as TNF-α and IL-6, and increase levels of anti-inflammatory compounds. The production of ketones during fasting, particularly β-hydroxybutyrate (BHB), has been shown to block the NLRP3 inflammasome, a key inflammatory signaling pathway. This reduction in chronic inflammation supports a more balanced and resilient immune response.

Gut Microbiome and Immune Modulation

The gut microbiome plays a crucial role in immune function, with beneficial bacteria producing compounds that support immune health. Fasting can significantly alter the composition and diversity of the gut microbiota. Studies have found that IF can increase the abundance of beneficial bacteria, such as Akkermansia, and boost the production of short-chain fatty acids (SCFAs), like butyrate. SCFAs have powerful anti-inflammatory properties and help maintain the integrity of the gut lining, preventing the leakage of harmful substances that can trigger inflammation.

Fasting's Complex Impact: Short-Term vs. Long-Term Effects

While the long-term regenerative effects are well-documented, fasting also has notable short-term impacts. During a fast, there can be a temporary redistribution of immune cells, with circulating cells moving to places like the bone marrow. When refeeding occurs, these cells surge back into circulation, leading to a regenerative flush of the immune system. A mouse study showed that a 24-hour fast led to a 90% decrease in monocytes, but the return of feeding caused a surge of these cells, which could potentially be problematic. However, this response may also be an adaptive mechanism designed to conserve resources during periods of scarcity. What you eat after a fast is also critical, as nutrient-dense foods replenish the body's resources for repair and regeneration.

Potential Risks and Who Should Avoid Intermittent Fasting

For some individuals, especially those with pre-existing conditions, intermittent fasting can carry risks. The transient increase in inflammation seen in some studies with prolonged fasting could pose a risk for individuals with specific cardiovascular conditions or coagulation disorders. Furthermore, fasting is not recommended for everyone. Individuals who are underweight, have low muscle mass, are pregnant or nursing, or have a history of eating disorders should avoid IF. Those with diabetes should proceed with caution and only under medical supervision due to the risk of severe hypoglycemia. As with any significant dietary change, consulting a healthcare professional is crucial.

Comparison: Fasting vs. Unrestricted Eating on Immune Health


Feature	Intermittent Fasting State	Unrestricted Eating State
Inflammation	Promotes anti-inflammatory responses; reduces pro-inflammatory markers (e.g., CRP, TNF-α).	Can be associated with chronic low-grade inflammation, especially with a high-calorie diet.
Cellular State	Induces autophagy, a state of cellular cleaning and repair.	Primarily in growth and proliferation mode; less focus on cellular repair.
Energy Source	Shifts from glucose to fat metabolism, producing ketones.	Relies primarily on glucose for energy, with less metabolic flexibility.
Gut Microbiome	Can increase diversity and promote beneficial, SCFA-producing bacteria.	Can lead to imbalances (dysbiosis) that may increase inflammation.
Hormonal Balance	Lowers insulin and IGF-1; increases Human Growth Hormone (HGH).	Sustained high insulin and IGF-1 levels.

Conclusion

While the science is still evolving, the evidence suggests that intermittent fasting can significantly influence and potentially improve immunity. The process involves multiple mechanisms, from triggering cellular cleanup through autophagy to reducing chronic inflammation and enhancing gut health. The cyclical process of fasting followed by refeeding promotes a state of immune rejuvenation. However, it is not a universally suitable practice and carries potential risks, particularly during prolonged periods. Individuals should always consult with a healthcare professional before beginning any new fasting regimen to ensure it aligns with their personal health needs and goals. By understanding the intricate interplay between dietary patterns and immune function, we can make more informed choices for long-term health and resilience. The research continues to uncover the many ways that fasting affects our biology, and its role as a therapeutic and preventative tool for immune health is an exciting area of study.

Outbound link: Learn more about autophagy and its cellular functions from scientific research: https://pmc.ncbi.nlm.nih.gov/articles/PMC8932957/

Frequently Asked Questions

During fasting, autophagy recycles old or damaged immune cells and their components. This leads to the regeneration of a newer, more efficient immune cell population when refeeding occurs, which can improve immune function.

Yes, research suggests that intermittent fasting can have anti-inflammatory effects by reducing the levels of pro-inflammatory cytokines and producing anti-inflammatory ketone bodies. Some studies have found significant reductions in markers like C-reactive protein (CRP).

Some studies, particularly in animals, suggest that fasting can lead to a temporary decrease in circulating immune cells. This may be part of an adaptive response to conserve energy, with cells returning to circulation upon refeeding. However, this could temporarily increase vulnerability to infection.

Fasting can positively alter the gut microbiome by increasing the diversity and abundance of beneficial bacteria. These changes can reduce intestinal inflammation and enhance gut barrier function, which is critical for a healthy immune system.

The most effective mode can vary. Time-restricted feeding (TRE) has shown promise in reducing inflammatory markers. More prolonged periodic fasting (e.g., 48-72 hours) is suggested by some researchers to promote the most significant immune cell regeneration, but also carries higher risks.

No, intermittent fasting is not suitable for everyone. People who are underweight, pregnant, or have conditions like diabetes or a history of eating disorders should avoid or consult a doctor first. The effects are highly individual and context-dependent.

Yes, the refeeding period is crucial. The body performs most of its regenerative work after a fast. The foods consumed during this time should be nutrient-dense to replenish resources and support the production of new, healthier immune cells.