Can fasting cause high bilirubin? Understanding the connection between nutrition and liver health

October 3, 2025 •

3 min read

A study published in the Journal of Clinical Pathology found a statistically significant increase in total serum bilirubin levels in fasting males compared to non-fasting males. This raises a critical question: Can fasting cause high bilirubin? The answer is yes, and understanding this link is vital for anyone considering fasting, especially those with pre-existing conditions.

Quick Summary

Fasting can temporarily elevate bilirubin by reducing the liver's processing efficiency and increasing intestinal reabsorption. This effect is more pronounced in individuals with Gilbert's Syndrome but is usually mild and reversible upon refeeding.

Key Points

Fasting Elevates Bilirubin: Fasting or severe caloric restriction is a known cause of temporarily elevated bilirubin levels in the blood.
Two Key Mechanisms: This increase is primarily due to the liver's reduced ability to extract bilirubin and increased reabsorption of it from the intestines.
Gilbert's Syndrome Risk: Fasting is a significant trigger for symptomatic episodes of high bilirubin and jaundice in individuals with Gilbert's Syndrome.
Effect is Reversible: The elevation in bilirubin caused by fasting is typically mild, temporary, and reverses upon resuming normal caloric intake, especially carbohydrates.
More Pronounced in Males: Studies have observed that fasting increases bilirubin levels more significantly in healthy males than in females.
Underlying Conditions Matter: People with pre-existing liver diseases like cirrhosis should be cautious, as fasting can cause more significant and dangerous spikes in bilirubin.
See a Doctor for Symptoms: Persistent or severe symptoms like jaundice, dark urine, and abdominal pain warrant medical attention to rule out other causes of hyperbilirubinemia.

What is Bilirubin?

Bilirubin is a yellowish pigment formed when old red blood cells break down. This process happens in the spleen and other parts of the reticuloendothelial system. Bilirubin then goes to the liver for processing before being excreted.

There are two main forms of bilirubin:

Unconjugated (Indirect) Bilirubin: The unprocessed form, not water-soluble, carried in blood by albumin.
Conjugated (Direct) Bilirubin: Processed by the liver to be water-soluble and ready for excretion in bile.

Conjugated bilirubin is transported via bile ducts to the small intestine and eliminated through stool. If this process is impaired, bilirubin builds up in the blood, causing hyperbilirubinemia, which can lead to jaundice (yellowing of skin and eyes).

The Link Between Fasting and High Bilirubin

Fasting and calorie restriction have been shown to increase serum bilirubin levels, a condition called fasting hyperbilirubinemia. This rise is typically mild and temporary in healthy people, returning to normal with regular eating.

Two main reasons explain this phenomenon:

Reduced Liver Uptake: During fasting, the liver becomes less efficient at clearing bilirubin from the blood, leading to unconjugated bilirubin accumulation.
Increased Intestinal Reabsorption: Fasting may increase the reabsorption of bilirubin from the gut. Gut bacteria can deconjugate bilirubin, which is then reabsorbed into the bloodstream, raising levels. This effect is reversed upon eating, especially carbohydrates.

Fasting and Gilbert's Syndrome

Fasting is a known trigger for high bilirubin in people with Gilbert's Syndrome. This genetic condition causes reduced activity of a liver enzyme (UGT1A1) that processes bilirubin. While those with Gilbert's Syndrome usually have slightly high unconjugated bilirubin, fasting can worsen this, potentially causing visible jaundice. Avoiding prolonged fasting is generally advised for these individuals.

Factors Influencing Fasting Hyperbilirubinemia

Several factors can affect how much fasting impacts bilirubin levels:

Duration of Fasting: Longer fasts correlate with a greater increase in bilirubin, particularly in males.
Gender: Studies indicate fasting causes a more significant bilirubin increase in males than females.
Underlying Liver Conditions: In those with pre-existing liver issues, fasting can dangerously raise bilirubin levels. Fasting is often not recommended for severe liver disease.
Caloric Intake: Very low-calorie diets can also increase bilirubin and trigger symptoms in susceptible individuals.

When to Be Concerned: Symptoms and Warning Signs

While a slight bilirubin increase from fasting is usually harmless, very high levels can signal a more serious issue. Consult a doctor if you experience persistent or severe symptoms:

Jaundice: Yellowing of skin and eyes.
Dark Urine: Resembling tea.
Pale Stools: Potentially indicating bile duct blockage.
Fatigue.
Abdominal Pain: Upper right side pain can suggest liver or gallbladder problems.
Fever and Chills.
Nausea and Vomiting.

Seek immediate medical help for severe abdominal pain, confusion, or easy bruising/bleeding.

Comparing Causes of High Bilirubin


Feature	Fasting-Induced High Bilirubin	High Bilirubin from Other Causes
Cause	Temporary metabolic changes from low calories.	Underlying liver disease (hepatitis, cirrhosis), bile duct obstruction (gallstones), or blood disorders.
Severity	Usually mild and temporary, worse with Gilbert's.	Variable severity depending on the cause.
Symptom Duration	Resolves soon after eating.	May be chronic until the cause is treated.
Underlying Condition	Normal physiological response; risk increased by Gilbert's Syndrome.	Often a sign of a disease requiring medical treatment.
Reversibility	Easily reversed by refeeding.	Depends on treating the underlying cause.
Treatment	None needed for mild cases; manage fasting duration and carbohydrate intake.	Specific to the cause (e.g., medication, surgery).

Conclusion: Managing Bilirubin and Your Diet

While fasting can cause high bilirubin, it's typically a mild, temporary response in healthy individuals. Those with Gilbert's Syndrome may experience a more significant increase and visible jaundice. Fasting can be risky for people with severe liver disease. For most, reintroducing food will normalize bilirubin levels quickly. If you have persistent jaundice or other worrying symptoms, see a healthcare provider to rule out serious conditions. A balanced diet and avoiding prolonged fasting, especially if sensitive, can help manage bilirubin and support liver health.

For more on bilirubin tests and results, visit the Cleveland Clinic website.

Frequently Asked Questions

Significant increases in serum bilirubin can occur within 12 to 24 hours of fasting. Studies show a positive correlation between the duration of fasting and the increase in bilirubin levels, particularly in males.

For healthy individuals, fasting hyperbilirubinemia is generally considered a mild and temporary physiological response that is not dangerous. Levels typically return to normal shortly after eating resumes.

Individuals with Gilbert's Syndrome should be cautious with prolonged or intermittent fasting, as it is a well-known trigger for increased bilirubin levels and potential jaundice. Consultation with a doctor is recommended for personalized advice.

Fasting-induced high bilirubin is a temporary effect caused by changes in liver processing and intestinal reabsorption. Other causes, like liver disease or bile duct obstruction, are pathological and require specific medical treatment.

Simply reintroducing food, particularly carbohydrates, is often enough to reverse fasting-induced hyperbilirubinemia and restore bilirubin levels to normal. Keeping well-hydrated also helps.

The most visible symptom is jaundice (yellowing of the skin and eyes). Other symptoms can include dark urine, pale stools, fatigue, abdominal pain, nausea, and fever.

While temporary increases from fasting are common, you should see a doctor if you have persistent jaundice, dark urine, pale stools, or severe symptoms like fever, confusion, or abdominal pain.