How Long Should I Fast to Reduce Inflammation?

October 22, 2025 •

3 min read

According to a 2024 study published by the National Heart, Lung, and Blood Institute, fasting for as little as 24 hours can increase levels of arachidonic acid, a chemical known to inhibit inflammation. While this evidence suggests short-term fasting can be beneficial, the optimal duration for how long should I fast to reduce inflammation varies and depends on the specific protocol and individual health status.

Quick Summary

This article explores the mechanisms behind fasting's effect on inflammation, analyzing the science behind various fasting durations, from intermittent protocols to prolonged fasts. It examines specific impacts on inflammatory markers, outlines potential risks, and provides practical, safe methods for incorporating fasting into an anti-inflammatory lifestyle.

Key Points

Start Short, Go Slow: Begin with time-restricted eating (12-16 hours) before attempting longer fasts to allow your body to adjust safely.
24-Hour Fast is a Sweet Spot: Fasting for around 24 hours has been shown to reduce inflammatory monocytes and oxidative stress, providing a measurable anti-inflammatory effect.
Prolonged Fasting Has Nuance: Extended fasts (48+ hours) may cause a temporary increase in inflammation markers during the fast itself, with benefits appearing during the refeeding period.
Refeeding is Critical: Reintroducing food slowly and with nutrient-dense, anti-inflammatory options maximizes the benefits and minimizes potential side effects after a longer fast.
Hydration is Non-Negotiable: Staying well-hydrated with calorie-free fluids is essential during any fast, and electrolytes may be necessary for durations over 24 hours.
Combine with an Anti-inflammatory Diet: Fasting is most effective when paired with a balanced, whole-foods diet during eating windows to limit the reintroduction of inflammatory triggers.

The Science of Fasting and Inflammation

Inflammation is a crucial part of the body's immune response, but when it becomes chronic, it can contribute to a host of diseases, including type 2 diabetes, heart disease, and autoimmune conditions. A key focus of research has been understanding how dietary interventions like fasting can influence this process. At a cellular level, fasting appears to modulate inflammation through several key mechanisms:

Reduction of pro-inflammatory cells: Fasting can lead to a significant drop in pro-inflammatory cells, such as monocytes, that drive the inflammatory response.
Activation of autophagy: This cellular "housekeeping" process involves the removal of damaged cell components, which can reduce sources of inflammation.
Changes in chemical mediators: As noted in recent research, fasting for 24 hours can increase blood levels of arachidonic acid, a molecule with anti-inflammatory properties.
Improvement in insulin sensitivity: Chronic inflammation is closely linked to insulin resistance. Fasting has been shown to improve insulin sensitivity, thereby indirectly reducing inflammatory markers.

Comparing Different Fasting Durations

The duration of a fast plays a significant role in its effects on inflammatory markers. What works for one person may not be suitable or safe for another. Here is a comparison of different fasting durations and their associated inflammatory effects:


Fasting Duration	Protocol Type	Primary Anti-inflammatory Mechanism	Impact on Inflammatory Markers	Potential Risks
12-16 hours	Time-restricted eating (TRE)	Supports circadian rhythm and gut health.	Consistent reduction in markers like C-reactive protein (CRP) over time.	Lower risk; primarily hunger, irritability.
24 hours	Intermittent Fasting (IF) / Eat-Stop-Eat	Reduces oxidative stress; initial drop in monocytes.	Modest reduction in inflammatory markers, can be transient.	Increased hunger, irritability, fatigue, especially for beginners.
48 hours or more	Prolonged Fasting	Significant metabolic shift; can activate deep autophagy.	Inconsistent results; some studies show a transient increase in markers like CRP before a reduction after refeeding.	Dehydration, dizziness, significant hunger, potential electrolyte imbalance. Not recommended without medical supervision for most.

The Role of Refeeding

For longer fasts, the period of refeeding is just as important as the fasting window itself. Some studies indicate that inflammatory markers like hsCRP can actually increase during a prolonged fast (48+ hours) but then decrease significantly below baseline levels during the refeeding phase. This suggests that the body's initial response to extended fasting can be pro-inflammatory, but the true anti-inflammatory benefits are realized when a nutrient-dense, anti-inflammatory diet is reintroduced. This critical refeeding window allows the body to properly repair itself and capitalize on the cellular cleansing (autophagy) that occurred during the fast.

Starting a Fasting Protocol Safely

Before starting any fasting regimen, especially for inflammatory conditions, it is crucial to consult a healthcare professional. For those beginning, a gradual approach is often the safest and most sustainable method.

Start with a shorter window: Ease into time-restricted eating, like a 12 or 14-hour fast, to allow your body to adapt.
Stay hydrated: Drinking plenty of water, herbal tea, or black coffee is essential to prevent dehydration, a common side effect. Electrolyte supplementation may be needed for fasts over 24 hours.
Consume nutrient-dense foods: During your eating window, focus on whole foods rich in anti-inflammatory compounds. This includes leafy greens, berries, fatty fish, and healthy fats from sources like olive oil.
Listen to your body: Pay attention to how you feel. Severe fatigue, dizziness, or nausea are signs to end the fast.
Reintroduce food mindfully: Break your fast with a small, easily digestible meal. Avoid large, processed, or sugary meals, which can cause digestive distress.

Conclusion

While evidence suggests fasting can reduce inflammation, particularly through intermittent fasting protocols, the optimal duration is not a one-size-fits-all answer. For many, a daily 16-18 hour fast provides consistent, long-term anti-inflammatory benefits without the risks associated with prolonged fasting. Short-term fasts of 24 hours also show promise, but research indicates longer fasts (48+ hours) can cause a temporary rise in inflammatory markers before a potential post-refeeding drop. The key is a gradual, consistent approach combined with a nutritious diet during eating periods. Always consult a doctor before starting any new fasting regimen to ensure it aligns with your health needs and conditions.

Authoritative Outbound Link

Learn more about the science of inflammation and the body's immune response at the National Institutes of Health website.

Frequently Asked Questions

Yes, research indicates that intermittent fasting can significantly reduce markers of inflammation like C-reactive protein (CRP), especially when practiced consistently alongside a healthy diet.

A recent review suggests that during prolonged fasts of 48 hours or more, inflammatory markers may temporarily increase. However, some studies show these markers decrease below baseline levels during the subsequent refeeding period.

The ideal schedule varies by individual. Time-restricted eating (e.g., 16/8 method) is a widely recommended, sustainable option for long-term benefits. For more significant shifts, a periodic 24-hour fast may be effective, but consult a doctor first.

During a 24-hour fast, your body first uses stored glucose for energy, then switches to using stored fat. This process, coupled with reduced pro-inflammatory monocytes, begins to lower overall inflammation and oxidative stress.

During fasting, nutrient deprivation activates autophagy, a cellular process that clears away damaged cells and molecules. By removing this cellular debris, autophagy helps to reduce internal sources of inflammatory signals.

Yes, especially with longer fasts. Risks include dehydration, electrolyte imbalance, dizziness, and muscle loss. Individuals with pre-existing conditions like diabetes or a history of eating disorders should not fast without medical supervision.

During a water-only fast, you can drink water, black coffee, and unsweetened herbal teas. For longer fasts, an electrolyte supplement may be recommended to prevent imbalances.