What happens to inflammation when you fast?

November 21, 2025 •

4 min read

While fasting is often touted for its anti-inflammatory effects, recent scientific reviews indicate the truth is more complex. The impact of fasting on inflammation depends heavily on the fasting duration, an individual's metabolic state, and the specific inflammatory markers measured.

Quick Summary

This article explores the nuanced relationship between fasting and inflammation, distinguishing between different fasting durations and their effects on the immune system. It covers the mechanisms behind anti-inflammatory benefits in shorter fasts and the acute pro-inflammatory response observed during prolonged fasting, including key inflammatory markers and immune cell behavior.

Key Points

Duration is Key: Short-term intermittent fasting typically reduces inflammation, while prolonged fasting (over 48 hours) can cause a temporary increase in inflammatory markers.
Autophagy for Repair: Fasting activates autophagy, a process that recycles damaged cellular parts and helps reduce chronic inflammation.
Inflammasome Suppression: Short fasts can inhibit the NLRP3 inflammasome, a key trigger for inflammatory responses.
Refeeding is Important: For prolonged fasts, the anti-inflammatory benefits may appear during the refeeding period, when inflammatory markers can drop below baseline.
Consider Pre-existing Conditions: Individuals with conditions like obesity or cardiovascular disease may experience a more pronounced inflammatory response during prolonged fasting and should exercise caution.
Arachidonic Acid Production: A 24-hour fast increases arachidonic acid, a chemical that inhibits inflammation.
Immune Cell Shift: Intermittent fasting can lead to a redistribution of circulating immune cells, contributing to reduced systemic inflammation.

The relationship between fasting and inflammation is far from a simple one, with scientific evidence revealing a dynamic and context-dependent process. Contrary to the popular belief that all fasting uniformly reduces inflammation, research suggests that the duration of fasting plays a critical role in determining the outcome.

The Anti-Inflammatory Effects of Short-Term Fasting

For many people practicing intermittent or shorter fasts (under 48 hours), the body's response is generally anti-inflammatory. This effect is driven by several key cellular and metabolic changes.

Activation of Autophagy

Cellular Housekeeping: Fasting triggers autophagy, a natural cellular 'housekeeping' process where the body removes and recycles damaged or old cellular components.
Immune System Modulation: By clearing out dysfunctional cell parts, autophagy helps modulate immune system activity and reduces the burden of chronic inflammation, which is often linked to accumulated cellular debris.

Suppression of Inflammasome Activity

NLRP3 Inflammasome: Studies show that shorter fasting periods can suppress the activity of the NLRP3 inflammasome, a protein complex that acts as an alarm for the immune system and triggers inflammation.
Key Chemical Messenger: Research from the National Institutes of Health (NIH) found that a 24-hour fast increases a blood chemical called arachidonic acid, which helps turn down this inflammasome activity.

Immune Cell Redistribution

Monocyte Levels: Some studies indicate that intermittent fasting can reduce the number of circulating monocytes, a type of white blood cell that contributes to inflammation. The monocytes that remain may also become less inflammatory.
Organ-Specific Effects: The immune benefits of shorter fasts are thought to influence multiple organs, including the brain, heart, and liver.

The Pro-Inflammatory Response in Prolonged Fasting

In stark contrast to shorter fasts, prolonged fasts (typically defined as 48 hours or more) often lead to a significant, acute increase in inflammatory markers. This is not necessarily a negative outcome but rather a complex, adaptive physiological response.

Rise in Inflammatory Markers

C-Reactive Protein (CRP): Many studies have observed a rise in CRP levels during extended fasting, particularly in individuals with higher baseline weights. However, some research notes that CRP levels can drop below baseline after a period of refeeding.
Pro-Inflammatory Cytokines: Levels of other inflammatory markers, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), also tend to increase during prolonged fasting, although findings have been less consistent.

Metabolic and Immune System Activation

Adaptive Stress: The temporary spike in inflammation during a prolonged fast is seen as an adaptive stressor, similar to a strenuous workout. The body, under stress, activates systemic responses, including immune-related pathways.
Adipose Tissue Remodeling: During extended fasts, the body mobilizes energy from fat stores. This can trigger an inflammatory signature in adipose tissue, potentially stimulating macrophage activity involved in lipid metabolism and remodeling.

The Refeeding Phase

The refeeding period after a prolonged fast is crucial. For some individuals, the inflammatory markers that spiked during the fast return to or even fall below baseline levels. This suggests that the body's metabolic reset during the fast, followed by the reintroduction of nutrients, may ultimately contribute to a reduced inflammatory state. The composition of the refeeding diet is also important, with evidence suggesting that a nutrient-dense, anti-inflammatory diet enhances benefits.

Comparison: Short-Term vs. Prolonged Fasting on Inflammation


Feature	Short-Term Fasting (e.g., 16-24 hours)	Prolonged Fasting (e.g., 48+ hours)
Inflammatory Markers	Generally reduced or no significant change.	Initial increase in markers like CRP, IL-6, and TNF-α.
Cellular Mechanism	Activation of autophagy and suppression of the NLRP3 inflammasome.	Acute adaptive stress response, adipose tissue remodeling, potential systemic immune activation.
Immune Cell Impact	Can reduce circulating monocytes and make them less inflammatory.	Involves complex immune system activation and redistribution of immune cells.
Post-Fasting Effect	Supports overall metabolic health and anti-inflammatory state.	Inflammatory markers may normalize or decrease below baseline during refeeding.
Primary Goal	Enhanced metabolic flexibility and cellular repair.	Metabolic reset and deep cellular cleansing through intense adaptive responses.
Primary Risk	Minimal for healthy individuals, but side effects like hunger and irritability are common.	Potential risks for elevated inflammatory markers, especially in at-risk individuals.

Conclusion: The Final Verdict

The effect of fasting on inflammation is multifaceted and depends on the specific protocol. Shorter, intermittent fasting periods, which often align with natural circadian rhythms, generally demonstrate an anti-inflammatory effect by promoting cellular repair mechanisms like autophagy and suppressing pro-inflammatory pathways. Conversely, prolonged fasts trigger an acute and transient pro-inflammatory response, an adaptive physiological reaction to stress. The key anti-inflammatory benefits of extended fasting often emerge during the refeeding phase, where inflammation markers may normalize or decrease. For this reason, those with pre-existing inflammatory or cardiovascular conditions should approach prolonged fasting with caution and medical supervision due to the initial increase in inflammatory markers. Understanding these distinctions is essential for anyone considering a fasting regimen. For comprehensive guidance on integrating anti-inflammatory foods into your diet during eating windows, the NIH offers valuable resources on diet and inflammation.

Frequently Asked Questions

No, the effect of fasting on inflammation is not uniform and depends on its duration. While shorter, intermittent fasts often reduce inflammation, longer or prolonged fasts (more than 48 hours) can initially cause an acute increase in inflammatory markers.

Intermittent fasting (typically under 48 hours) is generally associated with a reduction in inflammation by promoting cellular cleanup (autophagy). In contrast, prolonged fasting (48+ hours) often leads to a temporary increase in inflammatory markers, followed by a potential reduction during the refeeding phase.

Autophagy is a process where the body recycles damaged and old cellular components. It is triggered by fasting and plays a key role in modulating the immune system, thereby helping to reduce chronic inflammation.

Key inflammatory markers include C-reactive protein (CRP), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α). Studies show variable results depending on fasting duration, with prolonged fasts often causing a temporary increase in CRP.

Yes, for individuals with pre-existing conditions like atherosclerosis or obesity, the temporary rise in inflammatory markers during prolonged fasting could potentially exacerbate cardiovascular risk. Medical supervision is recommended for extended fasts, especially in at-risk individuals.

The refeeding phase is crucial. After a prolonged fast, inflammatory markers that initially spiked may normalize or even decrease below baseline, indicating that the body's reset has an overall positive effect on inflammation.

Choosing the right fasting protocol for your health status and incorporating a nutrient-dense, anti-inflammatory diet during eating windows can help. A diet rich in fruits, vegetables, and healthy fats is beneficial.