Which pulse causes lathyrism? An overview of grass pea toxicity

December 28, 2025 •

4 min read

Epidemics of a crippling paralytic disease, known as neurolathyrism, have been documented for centuries in regions facing drought and famine, and these outbreaks are directly linked to the excessive consumption of one specific pulse. Lathyrism is caused by consuming large quantities of the grass pea, also known as khesari dal (Lathyrus sativus), which contains a neurotoxin.

Quick Summary

Neurolathyrism is a neurological disorder resulting from prolonged, excessive consumption of the pulse Lathyrus sativus, or grass pea. The condition, characterized by irreversible spastic paralysis of the lower limbs, is caused by the neurotoxin β-ODAP. It primarily occurs during times of famine when this hardy legume becomes a dietary staple.

Key Points

Cause: Lathyrism is caused by prolonged, excessive consumption of the grass pea, also known as khesari dal (Lathyrus sativus).
Toxin: The responsible neurotoxin is β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP), which damages motor neurons.
Triggers: The disease typically arises during famines when the drought-resistant grass pea becomes a dietary staple.
Symptoms: The condition leads to irreversible spastic paralysis of the lower limbs, often progressing from a rigid gait to using crutches or crawling.
Prevention: Soaking, boiling, and discarding the water from the pulse can reduce the toxin content, and diversifying the diet is key to prevention.
Vulnerability: Poor, rural populations in regions like India, Bangladesh, and Ethiopia are most at risk due to reliance on this crop.
Research: Efforts are underway to breed low-toxin strains of grass pea to make it safer for consumption.

The culprit: Lathyrus sativus

The neurotoxin behind the paralysis

Lathyrism, specifically neurolathyrism, is caused by the long-term, excessive consumption of the grass pea, Lathyrus sativus. This hardy, drought-resistant legume, known as khesari dal in South Asia, contains a neurotoxic amino acid called β-N-oxalyl-L-α,β-diaminopropionic acid (β-ODAP). The toxicity is particularly pronounced when this pulse becomes a staple food source, especially in times of famine when other crops fail. The disease typically affects poor rural communities in regions like India, Bangladesh, and Ethiopia. The toxic compound β-ODAP is an excitotoxin that mimics the neurotransmitter glutamate, leading to excessive stimulation and eventual death of motor neurons in the central nervous system.

Why consumption rises during famines

Lathyrus sativus is often referred to as an "insurance crop" because it can grow reliably in harsh environmental conditions, including drought and flooding, where other crops would fail. This resilience makes it a crucial food source for survival during food shortages, which tragically increases the likelihood of excessive consumption. The combination of a high-β-ODAP diet, heavy physical labor, and certain nutritional deficiencies, such as a lack of sulfur-containing amino acids, increases the risk of developing lathyrism.

Symptoms and progression of neurolathyrism

The stages of motor impairment

The onset of neurolathyrism is often sudden, with early symptoms including muscle cramps and weakness in the legs. The condition progresses through several stages of increasing severity:

Mild stage (No-stick stage): The patient can walk unaided but may experience a rigid or jerky gait.
Moderate stage (One-stick or two-stick stage): The individual requires the use of one or two walking sticks for support.
Severe stage (Crawler stage): The paralysis becomes so debilitating that the person is forced to move around on all fours.

Irreversible damage

By the time symptoms become noticeable, the damage to the motor neurons is often irreversible. Neurological examination reveals spastic paraparesis—a partial paralysis characterized by increased muscle tone and stiffness in the lower limbs, exaggerated reflexes, and a characteristic "scissor gait" where the legs cross over each other. Unfortunately, there is no known cure, and treatment is primarily focused on rehabilitation and preventing further exposure.

Comparison of Lathyrus Sativus with other pulses


Feature	Lathyrus Sativus (Khesari Dal)	Common Pulses (e.g., Lentils, Chickpeas)
Toxicity	Contains the neurotoxin β-ODAP, causing neurolathyrism with excessive intake.	Generally non-toxic when consumed as part of a normal diet.
Drought Resistance	Highly resistant; often grows in harsh conditions where other crops fail.	Less resilient; often requires more favorable growing conditions.
Nutritional Value	High protein content, but the risk of toxicity limits its use as a staple food.	Excellent source of protein, fiber, and micronutrients without neurotoxic risks.
Preparation	Requires extensive processing (soaking, boiling, discarding water) to reduce toxin levels.	Standard cooking methods are sufficient for consumption.
Epidemic Risk	High risk during famines when it becomes a dietary staple.	No risk of neurolathyrism.

Detoxification and prevention

Processing methods to reduce toxicity

Several methods can significantly reduce the β-ODAP content in grass peas, though they do not guarantee complete elimination of the toxin. These traditional practices include:

Soaking: Soaking the seeds in water for several hours and then discarding the water can leach out a large portion of the water-soluble toxin.
Boiling or Parboiling: Boiling the seeds, discarding the cooking water, and repeating the process can further reduce toxicity.
Roasting: High-temperature roasting can destroy a significant percentage of the neurotoxin.

Long-term solutions

Preventing lathyrism requires a multi-pronged approach that extends beyond food preparation. It involves:

Dietary Diversification: Promoting a varied diet that does not rely excessively on a single food source, especially during periods of scarcity.
Breeding Low-Toxin Strains: Developing and distributing new varieties of grass pea that naturally have lower levels of β-ODAP.
Public Awareness: Educating at-risk communities about the dangers of over-relying on grass pea and the proper preparation methods.

Conclusion

Understanding which pulse causes lathyrism is crucial for public health, particularly in vulnerable communities. The culprit is the drought-resistant grass pea (Lathyrus sativus), which contains a potent neurotoxin called β-ODAP. While it serves as a life-saving food source during famines, its excessive consumption can lead to irreversible paralysis. By combining traditional detoxification methods with modern approaches like breeding low-toxin strains and promoting diverse diets, we can mitigate the devastating effects of this preventable disease. It highlights the delicate balance between ensuring food security and safeguarding public health, especially in the face of climatic and economic instability. Continued research into the mechanisms of β-ODAP toxicity and the development of safer grass pea varieties is paramount to eradicating this historic affliction.

Authoritative Link: MedLink Neurology on Lathyrism

Frequently asked questions

Frequently Asked Questions

Lathyrism is a crippling neurological disorder caused by excessive consumption of the grass pea, Lathyrus sativus. It leads to irreversible paralysis of the lower limbs and affects both humans and animals.

The pulse that causes lathyrism is the grass pea (Lathyrus sativus), which is also known by names such as khesari dal or chickling pea.

The neurotoxin found in khesari dal is β-N-oxalyl-L-α,β-diaminopropionic acid, commonly abbreviated as β-ODAP.

β-ODAP acts as an excitotoxin, overstimulating and eventually destroying the motor neurons responsible for controlling the lower limbs. This damage to the central nervous system results in spastic paralysis.

Initial symptoms can include muscle cramps in the calves, leg weakness, a feeling of heaviness in the legs, and occasional trembling. The onset can be sudden and triggered by physical exertion.

Some traditional processing methods, like soaking, boiling, and discarding the water, can significantly reduce the toxin levels in grass peas. However, these methods are not 100% effective, and complete prevention requires a diversified diet.

No, while some species like Lathyrus sativus cause neurolathyrism, other related species contain different toxins that cause conditions like osteolathyrism, which affects connective tissues, not the nervous system.