The Toxic Culprit: ODAP in Grass Pea
Lathyrism, particularly the neurological form known as neurolathyrism, is caused by the overconsumption of legumes from the genus Lathyrus. The primary offender is Lathyrus sativus, commonly called the grass pea or khesari dal. This hardy, drought-resistant crop is often consumed in large quantities during times of food scarcity, leading to a build-up of the toxic compound in the body.
The Role of ODAP
The direct cause of neurolathyrism is the neurotoxin β-N-oxalyl-L-α,β-diaminopropionic acid, or β-ODAP. ODAP acts as an excitotoxin, overstimulating glutamate receptors in nerve cells, leading to neuronal damage and death. This primarily affects upper motor neurons controlling the lower limbs. The toxin also disrupts mitochondria and increases oxidative stress, further damaging neurons.
Why does ODAP become a problem during famine?
During periods of drought and famine, the grass pea is often one of the only crops that survives. Relying on a diet consisting of a third or more of grass pea for several months can lead to toxic ODAP accumulation, unlike standard diverse diets.
Types of Lathyrism and Causative Toxins
While neurolathyrism is the most well-known form, two other types of lathyrism result from different toxins found in other Lathyrus species.
| Type of Lathyrism | Causative Toxin | Primary Source | Affected Tissue |
|---|---|---|---|
| Neurolathyrism | β-ODAP (BOAA) | Lathyrus sativus (Grass Pea) | Motor neurons, spinal cord |
| Osteolathyrism | Beta-aminopropionitrile (BAPN) | Lathyrus odoratus (Sweet Pea) | Connective tissues, bones |
| Angiolathyrism | Beta-aminopropionitrile (BAPN) | Lathyrus odoratus (Sweet Pea) | Blood vessels |
Reducing the Risk of Lathyrism
Effective strategies exist to reduce lathyrism risk, focusing on lowering ODAP concentration in food.
Best Practices for Reducing ODAP Content:
- Soaking: Soaking peas for 12+ hours and discarding the water significantly reduces ODAP, as the toxin is water-soluble.
- Boiling and Parboiling: Cooking in boiling water and discarding it before further cooking also lowers toxin levels and denatures protease inhibitors.
- Mixing with Other Grains: Consuming grass pea as part of a mixed grain diet dilutes ODAP intake. Keeping consumption below 30% of the diet dramatically reduces risk. Sulphur-containing amino acids from other cereals may offer protection.
- Avoid Immature Seeds: Immature seeds have higher ODAP concentrations.
- Fermentation: Traditional fermentation can help break down neurotoxic compounds.
Modern Developments and Considerations
Increased awareness and food security have decreased lathyrism cases in some areas, but risk remains in vulnerable regions. Research is ongoing to develop low-toxin grass pea varieties that retain hardiness (Source: John Innes Centre). Individual susceptibility varies based on factors like nutritional status; diets low in sulphur-containing amino acids may enhance ODAP's effects.
Conclusion
Lathyrism occurs due to the long-term, excessive intake of specific toxic compounds from Lathyrus legumes, primarily β-ODAP from the grass pea. This condition, causing spastic leg paralysis, often arises during famine when these resilient crops are a dietary staple. While preventable through preparation methods like soaking, boiling, and diet diversification, it remains a public health concern for food-insecure communities. Developing safer crop varieties and improving nutritional knowledge are vital for global risk mitigation.
