How long to fast to reduce cholesterol?

November 18, 2025 •

4 min read

According to a 2015 review, alternate-day fasting over 3–12 weeks can lead to significant reductions in total cholesterol and triglycerides. For those wondering, 'how long to fast to reduce cholesterol?', the answer depends on the specific fasting protocol and individual health factors.

Quick Summary

This article explores the necessary duration for fasting to effectively lower cholesterol. It compares different intermittent fasting methods, their typical timelines, and discusses the scientific basis for metabolic changes that impact lipid profiles.

Key Points

Start Intermittent Fasting First: Aim for daily 12 to 16-hour fasts and consistently follow the protocol for several weeks to see initial benefits.
Alternate-Day Fasting is Highly Effective: Studies show that alternate-day fasting for 3–12 weeks can significantly lower total cholesterol and triglycerides.
Longer Fasts Require Medical Supervision: Prolonged fasts (over 24 hours) should only be done under a doctor's care, as they can temporarily increase cholesterol or pose other risks.
Healthy Diet is Crucial: The benefits of fasting are amplified by a healthy, balanced diet during eating windows; fasting is not a quick fix for poor eating habits.
Weight Loss Plays a Major Role: A large part of the cholesterol-lowering effect from fasting is a result of the associated weight reduction.
Consult a Doctor Before Starting: Always talk to a healthcare professional before beginning a fasting regimen, especially if you have pre-existing health conditions.

Understanding the Metabolic Shift

Fasting initiates a crucial metabolic change in the body that can influence cholesterol levels. After not eating for 10-16 hours, your body switches from burning glucose (sugar) for energy to burning stored fat, a state known as ketosis. This metabolic flexibility is a key mechanism through which fasting affects your lipid profile. This switch can lead to improvements in various blood lipid markers, including LDL ('bad') cholesterol and triglycerides. However, the speed and extent of these changes depend on the fasting method and duration.

Fasting Timelines for Cholesterol Reduction

Intermittent and Alternate-Day Fasting

For most people, sustainable, long-term results come from consistent practice rather than a single event. Intermittent fasting (IF) is a popular approach that cycles between periods of eating and fasting.

16:8 Method: A 16:8 protocol involves fasting for 16 hours and eating during an 8-hour window each day. Most individuals begin to notice changes or feel the benefits within two to four weeks as their body adapts. For improving cholesterol, the consistent metabolic shift over several weeks is what drives the positive changes.
Alternate-Day Fasting (ADF): With ADF, you alternate between days of eating normally and days of significant calorie restriction. Studies have shown significant reductions in total cholesterol (10–21%) and triglycerides (14–42%) within 3 to 12 weeks of starting this regimen.
Regular 12-Hour Fasts: A study from Aga Khan University showed that fasting for about 12 hours three days per week for six weeks resulted in improved lipid profiles, including significant reductions in total cholesterol and LDL cholesterol, along with increases in HDL ('good') cholesterol.

Longer Fasting Durations and Cautions

Prolonged fasting, which involves extended periods of minimal or no caloric intake, should only be undertaken under medical supervision due to health risks. The research on prolonged fasting and cholesterol shows varied and sometimes contradictory results.

Short-Term Prolonged Fasts: Some studies, such as those on 24-hour water fasts, have actually shown a temporary increase in cholesterol levels. This is thought to be a result of the body mobilizing stored fat, and the effect is typically short-term.
Medically Supervised Prolonged Fasts: A 14-day medically supervised fast demonstrated significant long-term reductions in LDL cholesterol and triglycerides in participants. This highlights that while short, unmonitored prolonged fasts can cause temporary spikes, carefully managed longer fasts can lead to more significant reductions.

The Negative Effects of Extreme Fasting

It is important to differentiate between intermittent fasting and extreme calorie restriction, such as eating only one meal a day (OMAD). Some studies suggest that the OMAD pattern may lead to increased total and LDL cholesterol levels compared to less restrictive methods, along with other health issues like heightened blood pressure.

Comparison of Fasting Methods for Cholesterol


Method	Typical Duration for Results	Potential Cholesterol Impact	Safety & Considerations
Time-Restricted Feeding (e.g., 16:8)	2–4 weeks for initial changes, ongoing for sustained benefits.	Potential for modest improvements in LDL and HDL cholesterol over time.	Generally considered safe and manageable for most healthy adults. Good for long-term consistency.
Alternate-Day Fasting (ADF)	3–12 weeks for significant reductions.	Significant reductions in total cholesterol and triglycerides.	More intense and potentially harder to sustain than TRF. Requires greater discipline.
Medically Supervised Prolonged Fasting	Can achieve significant reductions within 2–4 weeks, with longer fasts showing more marked effects.	Potential for significant reduction of LDL and triglycerides under specific protocols.	Requires medical supervision. Not for unmonitored at-home use, especially for prolonged periods.

Fasting is Not a Standalone Solution

While fasting can be a powerful tool, its cholesterol-lowering benefits are often intertwined with other factors. A healthy, balanced diet during eating periods is crucial for success. Many positive outcomes linked to fasting, such as reduced insulin resistance and improved lipid processing, are also driven by the overall weight loss that frequently accompanies a fasting regimen. Focusing on a holistic approach that includes a nutritious diet and regular exercise is more effective than relying on fasting alone.

Conclusion: Finding the Right Fasting Duration

There is no single, universally optimal fasting duration to reduce cholesterol. For most people, a manageable intermittent fasting schedule, such as the 16:8 method, consistently practiced over several weeks, is a safe and effective starting point. For more significant or rapid changes, alternate-day fasting over a few months has shown robust results. Prolonged fasting should only be attempted with professional medical supervision. Remember to consult your healthcare provider to discuss the best approach for your specific health needs before starting any new fasting regimen. You can read more about a 14-day study on long-term fasting at the NIH website: NIH Study on Long-Term Fasting.

Note: It is crucial to monitor your cholesterol levels with blood tests (lipid profiles) before and during any new diet or fasting protocol to assess its impact.

Frequently Asked Questions

For a standard lipid panel, a healthcare professional will typically ask you to fast for 9 to 12 hours before the blood draw. This ensures the triglycerides from recent meals do not distort the results.

Yes, research suggests that various forms of intermittent fasting can be effective for lowering high cholesterol. Many studies have shown it can reduce LDL ('bad') cholesterol and triglycerides, and in some cases, increase HDL ('good') cholesterol.

Not necessarily. While some medically supervised, prolonged fasts have shown positive results, other short-term prolonged fasts (like a 24-hour water fast) can cause temporary increases in cholesterol as fat is mobilized. Intermittent fasting is generally a safer and more sustainable approach for many people.

Yes, a 24-hour water-only fast can temporarily increase cholesterol levels. This is a short-term effect caused by the body mobilizing fat stores for energy. This is distinct from the long-term, sustained benefits seen with regular intermittent fasting.

Some studies on the OMAD pattern have shown potentially adverse effects, including increased total and LDL cholesterol and higher blood pressure, compared to less restrictive methods. It may not be a suitable or safe method for everyone, especially those with pre-existing heart conditions.

There is no single 'fastest' way, and focusing on sustainability is more important than speed. However, some evidence suggests alternate-day fasting (ADF) can produce significant cholesterol and triglyceride reductions within 3-12 weeks. For most, a consistent approach like the 16:8 method is a safer and more practical option.

Fasting helps lower cholesterol by triggering a metabolic switch where the body burns stored fat for energy instead of glucose. This shift can improve the overall lipid profile. Additionally, fasting often leads to weight loss, which is a major contributing factor to lower cholesterol levels.