Why do fava beans cause hemolytic anemia? Unraveling Favism

October 17, 2025 •

4 min read

Affecting around 400 million people worldwide, Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme deficiency in humans. The deficiency means that when susceptible individuals consume fava beans, a condition called favism can be triggered, which causes hemolytic anemia. This occurs due to the oxidative compounds within the beans attacking and destroying the red blood cells.

Quick Summary

Favism is an acute hemolytic anemia triggered by consuming fava beans in people with G6PD deficiency. This genetic enzyme defect prevents red blood cells from protecting themselves against oxidative stress, leading to their rapid destruction. Toxic compounds in the beans, known as vicine and convicine, are the direct cause of this reaction.

Key Points

Genetic Defect: Favism is caused by a genetic deficiency of the G6PD enzyme, which is critical for protecting red blood cells from oxidative damage.
Oxidative Compounds: Fava beans contain natural glycosides, vicine and convicine, which are metabolized into strong oxidizing agents that attack red blood cells.
Impaired Antioxidant Production: The lack of functional G6PD means red blood cells cannot produce enough of the protective antioxidant glutathione, making them susceptible to damage.
Symptoms of Hemolysis: A favic attack results in hemolytic anemia, causing fatigue, jaundice, dark urine, and potentially severe complications.
Prevention is Key: The best way to manage favism is to completely avoid fava beans and other known oxidative triggers.
Prevalence: G6PD deficiency is most prevalent in populations from African, Mediterranean, Middle Eastern, and Asian descent.
Severe Cases: In infants and young children, favism can be more severe and potentially fatal, with a higher ratio of ingested beans to body mass.
Variable Reaction: Not all G6PD-deficient individuals react to fava beans, and the severity can depend on the specific genetic variant and amount consumed.

The Genetic Root: Understanding G6PD Deficiency

Favism is not a condition that affects everyone who eats fava beans. Instead, it is a specific manifestation of an inherited genetic disorder known as glucose-6-phosphate dehydrogenase (G6PD) deficiency. G6PD is a crucial enzyme found in all red blood cells. Its primary role is to produce a molecule called NADPH (Nicotinamide adenine dinucleotide phosphate), which in turn helps maintain high levels of a powerful antioxidant, glutathione. Glutathione is essential for neutralizing harmful reactive oxygen species, also known as free radicals, that naturally form within red blood cells.

In individuals with a G6PD deficiency, the red blood cells lack this critical protective mechanism. When exposed to oxidative stressors, their cells are ill-equipped to defend against damage. This leaves the cell membrane vulnerable to attack, leading to the premature breakdown of red blood cells, a process called hemolysis. The severity of the deficiency varies depending on the specific genetic variant inherited. This is why some people with the deficiency may have no symptoms unless triggered, while others experience severe reactions. The condition is X-linked, meaning it affects males more frequently, but females who are carriers can also be symptomatic.

The Toxic Trigger: Vicine and Convicine

Fava beans (Vicia faba) contain naturally occurring glycoside compounds called vicine and convicine. When ingested, these are metabolized in the body into highly potent oxidizing agents known as divicine and isouramil. For a person with normal G6PD function, the body can easily neutralize these chemicals. The G6PD enzyme ensures a sufficient supply of reduced glutathione to counteract the oxidative damage.

However, in a G6PD-deficient individual, the system is overwhelmed. Without adequate G6PD, the red blood cells cannot produce enough NADPH to regenerate the protective glutathione. The influx of oxidants from the divicine and isouramil quickly damages the red blood cell membranes, leading to their rupture. This massive destruction of red blood cells is the core of the hemolytic anemia observed in favism.

The Process of Hemolysis

The destruction of red blood cells in a favic attack can be a rapid and severe event. This process is categorized into intravascular and extravascular hemolysis. Intravascular hemolysis happens within the blood vessels, as the red blood cells burst directly. Extravascular hemolysis occurs when damaged red blood cells are cleared from circulation by macrophages in the spleen. This rapid, widespread destruction leads to the classic symptoms of a hemolytic crisis.

Symptoms of a Favic Attack

Anemia and Fatigue: The rapid decrease in red blood cells leads to severe anemia, causing extreme tiredness and pallor.
Jaundice: The breakdown of hemoglobin from the destroyed red blood cells releases bilirubin, which accumulates in the blood and causes yellowing of the skin and eyes.
Dark Urine: The body excretes excess bilirubin and other byproducts of red blood cell destruction through the urine, giving it a dark, tea-colored appearance.
Abdominal or Back Pain: The rapid breakdown of red blood cells and the body's reaction can cause discomfort and pain.
Enlarged Spleen: The spleen works overtime to clear damaged red blood cells from the blood, causing it to become enlarged and tender.

Management and Prevention

There is no cure for G6PD deficiency, and the most effective treatment for favism is prevention. Individuals diagnosed with the condition must avoid fava beans and other potential triggers, such as certain medications and chemicals. This is particularly critical in regions where G6PD deficiency is prevalent and fava beans are a dietary staple.

Comparison of Normal vs. G6PD-Deficient Metabolism


Feature	Normal G6PD Individual	G6PD-Deficient Individual
G6PD Enzyme	Fully functional and abundant.	Deficient or functionally impaired.
NADPH Production	High levels, ensuring antioxidant defense.	Insufficient levels, compromising defense.
Glutathione Levels	Effectively maintained in reduced, active form.	Depleted under oxidative stress.
Oxidative Stress Tolerance	Red blood cells withstand oxidative compounds.	Red blood cells highly vulnerable to oxidative damage.
Fava Bean Exposure	No adverse hemolytic reaction.	Triggers acute hemolytic anemia (favism).
Red Blood Cell Lifespan	Normal, around 120 days.	Prematurely destroyed, leading to shorter lifespan.

Conclusion

Favism is a serious and potentially life-threatening condition caused by a genetic inability to counter the oxidative stress induced by fava beans. For individuals with a G6PD deficiency, the natural compounds vicine and convicine in the beans act as potent oxidants, overwhelming the red blood cells' weakened defenses and causing them to burst. The resulting hemolytic anemia can range from mild to severe, and in some cases, can lead to complications like kidney failure. The key to managing this condition is a clear diagnosis, diligent avoidance of triggers, and, in severe cases, medical treatment including blood transfusions. Public awareness and screening, especially in high-prevalence areas, are crucial preventative measures.

Frequently Asked Questions

Favism is a specific type of acute hemolytic anemia triggered by the consumption of fava beans in individuals who have a genetic deficiency of the enzyme glucose-6-phosphate dehydrogenase (G6PD).

Individuals with a genetic G6PD deficiency are at risk. This condition is most common among people of African, Mediterranean, Middle Eastern, and Southeast Asian descent, which is where fava beans are also a common part of the diet.

No, cooking does not eliminate the risk. The toxic compounds in fava beans, vicine and convicine, are relatively heat-stable and remain active after cooking, still posing a risk to G6PD-deficient individuals.

Symptoms typically appear 24-48 hours after eating fava beans and include fatigue, pale skin, jaundice (yellowing of skin and eyes), dark-colored urine, abdominal pain, and an enlarged spleen.

G6PD deficiency is diagnosed with a simple blood test that measures the level of the G6PD enzyme in red blood cells. Newborn screening for the condition is also common in high-risk regions.

There is no cure for the underlying G6PD deficiency. However, favism attacks can be managed by avoiding triggers. In severe cases of hemolytic anemia, blood transfusions and supportive care may be necessary.

While fava beans are the most significant and confirmed trigger, most other beans and legumes are not an issue. However, individuals with G6PD deficiency should always consult a doctor or dietician for personalized advice.