How long do you need to fast to reduce inflammation? A deep dive into nutrition diets and inflammatory markers

October 16, 2025 •

4 min read

According to a 2024 study by the National Heart, Lung, and Blood Institute (NHLBI), fasting for just 24 hours can increase levels of arachidonic acid, a lipid that helps inhibit inflammation. However, the question of how long do you need to fast to reduce inflammation is complex and the answer depends on the type of fasting and individual health status. Research on the effects of fasting on inflammatory markers shows conflicting results, especially when comparing intermittent versus prolonged fasting periods.

Quick Summary

This article examines the evidence behind different fasting durations and their impact on reducing inflammation. It explores the mechanisms, risks, and benefits of short-term and prolonged fasting, reviewing current human studies that show varied results on inflammatory markers like CRP, TNF-alpha, and IL-6. The text also contrasts fasting with anti-inflammatory diets and discusses the importance of refeeding protocols.

Key Points

Duration is Key: Short-term intermittent fasting (16-24 hours) shows acute anti-inflammatory benefits, while prolonged fasting (48+ hours) may cause a temporary increase in inflammation.
Refeeding Matters: The refeeding phase following prolonged fasting is crucial, as inflammatory markers can normalize or decrease below baseline when consuming healthy, anti-inflammatory foods.
Mechanisms Vary: Short-term fasting appears to reduce inflammation by suppressing the NLRP3 inflammasome and decreasing inflammatory monocytes.
Prolonged Fasting Risks: Extended fasting carries risks, including nutrient deficiencies and potential cardiac stress, and may not be suitable for individuals with pre-existing conditions.
Personalized Approach: Due to inconsistent study results and individual health differences, a tailored approach to fasting is necessary. Consulting a doctor is recommended, particularly for prolonged fasts.
Holistic Strategy: Combining intermittent fasting with a whole-food, anti-inflammatory diet is a safer and more comprehensive strategy for managing chronic inflammation.
Health Status Influences Results: The effect of fasting on inflammation is context-dependent and influenced by an individual's baseline health, weight, and metabolic state.

Understanding the Complex Relationship Between Fasting and Inflammation

Fasting has long been recognized for its potential health benefits, but its specific impact on inflammation is a subject of ongoing scientific research and debate. The body’s inflammatory response is a complex process involving various signaling proteins and immune cells. Acute inflammation is a natural defense mechanism against injury or infection, but chronic low-grade inflammation is linked to numerous diseases, including type 2 diabetes, heart disease, and autoimmune conditions. The duration of a fast plays a crucial role in determining its inflammatory effects, with studies showing different outcomes for shorter versus longer periods of calorie restriction.

Short-term intermittent fasting (16–24 hours)

Intermittent fasting (IF) typically involves restricting food intake to a specific window of time, such as the 16:8 method, where a person eats for eight hours and fasts for 16. Research suggests that these shorter fasting periods can have anti-inflammatory effects through several mechanisms:

Monocyte reduction: A study published in 2019 found that a short fasting period of about 19 hours led to a strong drop in blood monocytes, a type of white blood cell that indicates inflammation.
NLRP3 inflammasome suppression: Short-term fasting can suppress the activity of the NLRP3 inflammasome, a multiprotein signaling complex that triggers inflammation. This mechanism is thought to involve an increase in arachidonic acid during fasting, which acts to inhibit inflammasome activity.
Enhanced cellular repair (autophagy): Fasting triggers autophagy, a process where the body cleans out damaged cells to regenerate newer, healthier ones. This process helps reduce cellular stress and dysfunction, which can drive inflammation.

Prolonged fasting (48 hours or more)

While intermittent fasting shows promise, the effects of prolonged fasting (lasting 48 hours or longer) on inflammatory markers are more complex and sometimes contradictory. A recent systematic review published in Ageing Research Reviews challenged the belief that prolonged fasting consistently reduces inflammation, finding that most studies reported either no change or an increase in key inflammatory biomarkers like C-reactive protein (CRP), IL-6, and TNF-alpha during the fasting period itself.

This acute inflammatory response may be part of an adaptive, transient mechanism as the body shifts its energy sources. For example, studies have shown that while hs-CRP levels may rise during prolonged water-only fasting, they can decrease below baseline levels during the refeeding period. Other studies, however, report that some inflammatory markers remain elevated even after refeeding.

Refeeding and Inflammation

The refeeding process after a fast appears to be a critical factor influencing inflammatory markers. Some studies have noted a decrease or normalization of inflammatory markers post-refeeding, suggesting that the pro-inflammatory spike seen during prolonged fasting might be temporary. The type of food introduced during refeeding is also important. Anti-inflammatory diets, rich in whole plant foods, can further aid in normalizing inflammatory levels and supporting overall metabolic health.

Comparison of Fasting Durations and Anti-Inflammatory Outcomes


Feature	Short-term Fasting (16–24 hours)	Prolonged Fasting (≥48 hours)	Anti-inflammatory Diet	Re-feeding Phase
Inflammatory Effect	Can show acute anti-inflammatory benefits.	Often triggers an acute pro-inflammatory response.	Long-term reduction of chronic inflammation.	Can reverse the pro-inflammatory effects of prolonged fasting.
Mechanism	Monocyte reduction, NLRP3 inflammasome suppression, increased arachidonic acid, and autophagy.	Metabolic stress, changes in adipose tissue, release of inflammatory proteins.	Reduced intake of pro-inflammatory foods; increased intake of antioxidants.	Dietary intervention to normalize inflammatory proteins and stabilize metabolic functions.
Duration	Daily or a few times per week.	Extended periods, such as 3-10+ days, usually medically supervised.	Continuous, consistent dietary pattern.	Follows a fasting period; duration varies based on the fast's length.
Risks	Generally low risk for healthy individuals.	High risk, including electrolyte imbalances, nutrient deficiencies, and cardiac stress.	Generally low risk; promotes nutrient-dense intake.	High risk if refeeding is done improperly with junk food or overeating.
Suitability	Wide suitability, including for metabolic syndrome.	Not suitable for individuals with pre-existing conditions like heart disease.	Highly suitable for promoting long-term health.	Crucial for transitioning safely and maximizing benefits.

Factors Influencing Fasting Outcomes

Beyond the duration of the fast, several factors influence its effect on inflammation. An individual’s health status, including baseline inflammatory levels and body composition, can significantly alter the response to fasting. For example, studies suggest that individuals who are overweight or obese may experience a more pronounced pro-inflammatory spike during prolonged fasts. The heterogeneity in human studies—due to differences in fasting protocols, study populations, and inflammatory marker measurement—also makes it challenging to draw universal conclusions.

For many, a less extreme approach involving time-restricted eating (e.g., 16:8) may be safer and more sustainable for long-term health and inflammation management. Combining intermittent fasting with a whole-food, anti-inflammatory diet provides the most comprehensive strategy, promoting weight loss and decreasing inflammatory load through a nutrient-rich intake.

Conclusion

The time required to fast to reduce inflammation is not a simple, single answer. While research suggests that short-term intermittent fasting (16–24 hours) can induce acute anti-inflammatory effects by altering immune cell activity, prolonged fasting of 48 hours or more may temporarily increase systemic inflammatory markers. However, this response can be followed by a normalization or reduction of inflammation during the refeeding phase, especially when transitioning to an anti-inflammatory diet. Given the varied and sometimes contradictory findings in human studies, personalized approaches are essential. Consulting a healthcare professional before attempting any prolonged fasting protocol is critical, especially for individuals with underlying health conditions. For those without contraindications, a combined approach of intermittent fasting and a consistent anti-inflammatory diet offers a balanced and safer path toward managing chronic inflammation.

Frequently Asked Questions

Intermittent fasting (16–24 hours) has been shown to produce acute anti-inflammatory effects, such as reducing inflammatory monocytes. In contrast, prolonged fasting (48+ hours) often leads to a temporary increase in inflammatory markers during the fast itself, which may then normalize or decrease below baseline after a proper refeeding period. For most people, a less extreme intermittent fasting approach is safer and sufficient for managing inflammation.

The mechanism involves several pathways. Short-term fasting can suppress the NLRP3 inflammasome, a complex that triggers inflammation. It also increases levels of arachidonic acid, a lipid that helps inhibit inflammation. Additionally, fasting stimulates autophagy, a cellular repair process that removes dysfunctional proteins and reduces cellular stress that contributes to inflammation.

Yes, prolonged fasting (48+ hours) comes with significant risks. Recent studies indicate that it can induce an acute inflammatory response, increasing markers like CRP, especially in overweight individuals. Risks include potential cardiac stress, electrolyte imbalances, and nutrient deficiencies. It is not recommended without medical supervision, especially for individuals with pre-existing conditions like heart disease.

Yes, the refeeding period is critical. For instance, some studies on prolonged fasting show that while inflammatory markers increase during the fast, they decrease below baseline levels after participants follow a guided refeeding plan with anti-inflammatory foods. Reintroducing healthy, whole foods post-fast can help normalize inflammatory levels and prevent a rebound effect.

An anti-inflammatory diet, rich in nutrient-dense foods like fruits, vegetables, nuts, and healthy fats, can significantly complement the benefits of fasting. While fasting provides periods of metabolic rest, a consistent anti-inflammatory diet reduces the overall inflammatory load on the body. This combined approach is a robust strategy for managing chronic inflammation.

You can combine a time-restricted eating schedule, like the 16:8 method, with an anti-inflammatory diet. Aim to fill your eating window with foods rich in antioxidants and omega-3s, such as berries, leafy greens, salmon, and seeds. Drink plenty of water during your fasting period and focus on whole, unprocessed foods to maximize benefits and avoid inflammatory triggers.

For most healthy individuals, combining an anti-inflammatory diet with intermittent fasting is safe and beneficial. However, some people may experience side effects like mood dips or decreased energy during fasting, especially if they are new to the practice. It is crucial to listen to your body and consult a healthcare provider to ensure it is appropriate for your health needs.