What are the side effects of Lathyrus sativus?

January 1, 2026 •

4 min read

An estimated 2.4% of the population in some endemic regions of Ethiopia has been affected by neurolathyrism, a devastating neurodegenerative disease caused by consuming large quantities of Lathyrus sativus. This hardy legume, often a lifeline during famine, contains a potent neurotoxin that can lead to permanent paralysis and other neurological damage. Understanding the specific side effects is crucial for preventing this severe and often irreversible condition.

Quick Summary

Prolonged and excessive consumption of the grass pea, Lathyrus sativus, can cause neurolathyrism, a neurodegenerative disorder resulting in progressive, irreversible paralysis of the lower limbs. The condition is caused by a neurotoxin called β-ODAP and is more prevalent during periods of drought and famine when this legume becomes a dietary staple. The risk is highest with high consumption and poor nutritional status.

Key Points

Neurolathyrism: The main side effect is a neurodegenerative disorder causing irreversible spastic paralysis of the lower limbs due to motor neuron damage.
Neurotoxin β-ODAP: The toxicity is caused by $\beta-N$-oxalyl-L-$\alpha$,$\beta$-diaminopropionic acid ($eta$-ODAP), an excitotoxin that overstimulates and kills nerve cells.
Risk Factors: High and prolonged consumption, particularly during famine or drought when the legume is a dietary staple, increases the risk significantly.
Mitigating Risks: Proper preparation, including soaking and boiling, can reduce the toxin content, although elimination is not guaranteed.
Early Symptoms: Initial signs include muscle cramps, leg weakness, and trembling, which can progress to severe paralysis if consumption continues.
Vulnerable Groups: Young adult males are often disproportionately affected, possibly due to higher consumption levels related to physical labor.
Not a General Toxin: Moderate consumption as part of a diversified diet is generally not harmful and does not cause neurolathyrism.
Research and Prevention: Breeding programs are actively developing low-ODAP varieties to make the crop safer and reduce the incidence of the disease.

Understanding the Neurotoxin in Lathyrus sativus

The primary culprit behind the serious side effects of Lathyrus sativus, also known as grass pea or chickling vetch, is a naturally occurring neurotoxic amino acid called $\beta-N$-oxalyl-L-$\alpha$,$\beta$-diaminopropionic acid, or $\beta$-ODAP. This compound acts as a powerful excitotoxin, mimicking the neurotransmitter glutamate in the brain but causing excessive stimulation and eventually leading to the death of motor neurons. The concentration of $\beta$-ODAP in the seeds can vary significantly depending on environmental factors, such as drought conditions, which can increase its potency.

The Mechanisms of Neurolathyrism

The accumulation of $\beta$-ODAP in the body over time targets and damages the upper motor neurons, particularly those within the pyramidal tracts of the spinal cord and motor cortex. This causes a gradual but progressive degeneration of the nerve tissue responsible for controlling movement in the lower limbs. The neurotoxic effects are not immediate and require prolonged, high-quantity consumption before symptoms manifest, often making the damage irreversible by the time it is noticed.

Symptoms of Neurolathyrism

The side effects of consuming Lathyrus sativus are primarily neurological and progress through several stages of severity. Early symptoms can be subtle and easily overlooked, while advanced stages can be completely debilitating.

Early-Stage Symptoms

Muscle cramps: Excruciating cramps, especially in the calf muscles, are often one of the first signs.
Leg heaviness: A sensation of weight or fatigue in the legs, even after minimal physical activity, may occur.
Weakness: Individuals may experience mild difficulty with movements like climbing stairs or rising from a squatting position.
Trembling: Occasional episodes of muscle trembling or hyper-irritability in the lower limbs can be observed.

Advanced-Stage Symptoms

Spasticity: A significant increase in muscle tone and stiffness develops, making movement awkward and difficult.
Scissoring gait: This characteristic walking pattern involves the thighs crossing over each other due to muscle stiffness and increased tone.
Hyperreflexia: The knee and ankle reflexes become exaggerated and may become clonic.
Progressive weakness and paralysis: Muscle weakness intensifies, eventually progressing to partial (paraparesis) or complete (paraplegia) paralysis of the lower limbs, which is often permanent and irreversible.
Muscle atrophy: Disuse and nerve damage lead to the wasting of leg muscle tissue.

Additional Health Complications

While the neurological damage is the most well-known, other complications can arise from prolonged consumption of Lathyrus sativus.

Cognitive effects: Some sources report potential memory loss and cognitive dysfunction in more severe cases.
Cardiovascular issues: Weak heartbeats and complications like aortic aneurysms have been associated with lathyrism.
Respiratory problems: Decreased breathing can occur in the most extreme cases.
Seizures: In rare instances, severe poisoning can lead to seizures and even death.

Risks and Mitigating Factors

The risk of developing neurolathyrism is not uniform. Several factors influence an individual's susceptibility and the severity of the disease.

Factors Increasing Risk

High and prolonged consumption: The disease is linked to using Lathyrus sativus as a dietary staple for several months, especially when it constitutes a high percentage (over 30%) of the daily caloric intake.
Environmental stress: Drought conditions can increase the level of $\beta$-ODAP in the grass pea, making the harvest more toxic.
Poor nutritional status: Malnutrition, particularly deficiencies in zinc and sulfur-containing amino acids, can exacerbate the neurotoxic effects.
Cooking methods: Inadequate cooking or preparation techniques can leave high concentrations of the toxin in the final dish. Boiling the seeds and discarding the water is a common detoxification method, but effectiveness can vary.

Mitigating Factors

Dietary diversification: Including other food sources, particularly cereals, can significantly lower the risk by reducing the amount of grass pea consumed.
Proper processing: Techniques like prolonged soaking and boiling can remove a large portion of the toxin. Fermentation and germination also show potential in reducing $\beta$-ODAP content.
Use of low-toxin varieties: Plant breeding programs are focused on developing varieties of Lathyrus sativus with lower $\beta$-ODAP levels to make the crop safer for consumption.

A Comparison of Lathyrism and Other Food-Related Neuropathies


Feature	Neurolathyrism (Lathyrus sativus)	Konzo (Cassava)	Guamanian ALS-PDC (Cycad nuts)
Toxin	$\beta$-ODAP	Cyanide compounds	BMAA and Cycasin
Mechanism	Excitotoxicity causing motor neuron death	Interferes with cellular respiration and nerve function	Complex neurotoxicity, potential excitotoxicity
Key Symptoms	Spastic paraparesis, muscle cramps, leg weakness, scissoring gait	Spastic paraparesis of lower limbs	ALS-like symptoms, parkinsonism, dementia
Primary Affected	Young adult males, particularly during famines	Women and children, especially during food crises	Endemic to specific populations in Guam
Reversibility	Irreversible nerve damage	Irreversible, but can stabilize with dietary change	Progressive and fatal

Conclusion

While Lathyrus sativus is a resilient and valuable crop in food-insecure regions, its inherent neurotoxicity poses a serious health threat if not handled correctly. The side effects, centered on the irreversible motor neuron degeneration known as neurolathyrism, can cause permanent paralysis and have significant socioeconomic consequences. The key to preventing these devastating effects lies in a multi-pronged approach: practicing careful food preparation techniques to reduce toxin levels, ensuring dietary diversity to limit dependency, and continuing the development of low-toxin grass pea varieties through scientific breeding programs. By addressing these factors, the risks associated with this vital crop can be mitigated, allowing vulnerable populations to benefit from its nutritional value without suffering its debilitating consequences.

Frequently Asked Questions

Neurolathyrism is a neurological disease caused by prolonged, excessive consumption of Lathyrus sativus (grass pea) seeds, leading to progressive and irreversible paralysis of the lower limbs.

The neurotoxic side effects are caused by a non-protein amino acid called $\beta-N$-oxalyl-L-$\alpha$,$\beta$-diaminopropionic acid, or $\beta$-ODAP, which is present in the seeds.

While methods like prolonged soaking and boiling can significantly reduce the level of the toxin $\beta$-ODAP, they do not guarantee complete removal. Proper preparation is critical but not a foolproof solution.

Consuming Lathyrus sativus in large quantities, typically when it forms a major part of the diet (over 30%) for an extended period of two to three months or more, is considered dangerous.

Individuals whose diets are heavily reliant on grass pea, particularly young adult males and those with poor nutritional status, are most at risk. This often occurs in drought and famine-stricken regions.

No, not all species in the Lathyrus genus are toxic to humans in the same way. The garden sweet pea (Lathyrus odoratus), for example, contains a different toxin that causes osteolathyrism, affecting connective tissues.

No, the nerve damage caused by neurolathyrism is typically irreversible. While stopping consumption can prevent the condition from worsening, existing damage cannot be undone.