Lathyrism: The Hidden Dangers of Kesari Dal Consumption

Tucked away in the pulse markets of central India is a humble legume with a troubled reputation. Known as Kesari dal, khesari dal, or grass pea, this hardy crop has fed poor families through droughts and famines for centuries. But when it dominates the plate for months on end, it can quietly cripple young, healthy adults, leaving them unable to walk. This silent disease has a name: lathyrism. Understanding why a single dal can cause irreversible paralysis is a lesson in nutrition, poverty, and public health all at once.

What is lathyrism? 🔗

Lathyrism is one of the oldest known neurotoxic disorders. It is caused by the prolonged and exclusive consumption of seeds from the genus Lathyrus, most commonly Lathyrus sativus, popularly called grass pea or Kesari dal. The disease has been recorded in Indian medical writing dating back to the sixteenth-century Bhavaprakasha and was mentioned by Hippocrates around 46 B.C., making it one of the earliest food-related illnesses ever documented.

The condition is technically called neurolathyrism when it affects the nervous system. It is mainly seen in poor, drought-prone regions of India, Bangladesh, Nepal, Ethiopia and China. In India, historical outbreaks have hit hardest in Madhya Pradesh, Uttar Pradesh, Bihar, Chhattisgarh and Odisha, where grass pea grows easily on poor soils and survives both flood and drought.

The toxin behind the disease 🔗

The culprit is a non-protein amino acid called β-N-oxalyl-L-α,β-diaminopropionic acid, abbreviated as β-ODAP or BOAA. This compound was identified in 1964 by scientists at the Indian Institute of Science in Bengaluru, ending a long search for the chemical cause of the disease.

β-ODAP closely mimics the neurotransmitter glutamate. Because of this resemblance, it overstimulates nerve cells in the spinal cord and motor cortex, a process called excitotoxicity. It also acts as a poison of the mitochondria, leading to excess cell death, especially in motor neurons. The result is permanent damage to the pyramidal tracts that control voluntary movement of the legs.

Why grass pea is grown despite the danger 🔗

Grass pea is remarkably tough. It can survive both flood and drought when no other crop will, and it is one of the cheapest sources of protein available to farming families. The seed is rich in protein, vitamin B1 and iron, which is why landless labourers in central India have long depended on it during lean months. The problem begins only when it becomes the staple food and crowds out other pulses, cereals and vegetables from the daily diet.

Symptoms of lathyrism 🔗

Lathyrism is not an acute poisoning. It develops gradually, usually after three to six months of consuming grass pea as the main dietary protein source. Most cases appear in young men between the ages of 15 and 45, who eat more and do heavier physical work than women and children. The disease is permanent once symptoms appear, so early recognition matters.

Early warning signs 🔗

The first complaints are vague. People describe heaviness in the legs, cramping after walking, and a sense that the knees are locking. Many sufferers report waking up at night with sudden muscle spasms in the calves and thighs. Because these signs look like ordinary fatigue from farm work, they are often ignored until walking becomes visibly difficult.

Progression to spastic paralysis 🔗

As nerve damage progresses, the muscles of the lower limbs become rigid and overactive. Sufferers develop a characteristic scissor-like gait, in which the legs cross over each other while walking and the toes drag on the ground. Atrophy of the gluteal muscles is a unique sign that doctors look for. In severe cases, the person can only walk on the balls of the feet, then with crutches, and finally cannot walk at all.

An important point for clinicians is that lathyrism almost never affects sensation, mental ability or the arms. Vision, speech and thinking remain normal. The damage is strictly to the upper motor neurons that supply the legs, which is why the disease is also called spastic paraparesis. There is no specific cure once the damage is done; treatment is limited to physiotherapy, assistive devices such as braces or crutches, nutritional rehabilitation and community-based rehabilitation programmes.

Other forms of lathyrism 🔗

While neurolathyrism is the most important form for public health, two related conditions exist. Osteolathyrism affects bones and connective tissues and is caused by the toxin BAPN (β-aminopropionitrile) found in sweet pea seeds, which interferes with collagen cross-linking. Angiolathyrism affects the walls of blood vessels and is also linked to BAPN exposure. Both are rare in humans compared to the neurological form.

Lathyrism in the Indian story 🔗

The disease has shaped public health policy in independent India in important ways. An outbreak in 1961 affected around 32,000 people in Madhya Pradesh alone, and after a severe drought in June 1975 the disease returned to affect about one lakh men in Madhya Pradesh and Bihar.

In response, the government banned the sale and storage of grass pea in 1961 under the Prevention of Food Adulteration Act, 1954, although Madhya Pradesh, Bihar and West Bengal did not follow the ban. Cultivation, however, was never stopped, and grass pea continued to be sold cheaply in rural markets. This is why the disease has never fully disappeared from central India, even though most modern Indians have never heard of it.

The shift toward low-toxin varieties 🔗

Indian scientists did not stop at banning the crop. Plant breeders at the Indian Agricultural Research Institute developed Pusa 24, the first low β-ODAP variety, in 1966. Newer varieties developed through ICAR collaborations, such as Ratan, Prateek and Mahateora, contain ODAP levels well below the threshold considered risky. In 2015, an expert committee recommended lifting the ban, citing the crop’s potential for food security amid climate change. The debate continues, balancing the nutritional value of a hardy pulse against the painful history of paralysed villagers.

Prevention of lathyrism 🔗

Because the nerve damage is permanent, prevention is everything. The good news is that the toxin can be substantially removed by simple kitchen techniques, and the disease can be eliminated by reasonable dietary diversity. The three pillars of prevention are safe preparation, dietary variety and public awareness.

Safe preparation at home 🔗

β-ODAP is highly water-soluble, which means it can be washed out of the seeds before cooking. The most effective traditional method is the soak-and-decant technique. Soaking the seeds or dal overnight and decanting the water before cooking eliminates about 90 per cent of the toxin. A study published in PubMed reported that if the legume is boiled for two hours and the water is then decanted, almost 85 per cent of the toxic amino acid is eliminated.

Other effective methods include roasting the seeds at around 140 °C for 15 to 20 minutes, steaming, and bacterial or fungal fermentation, all of which significantly reduce β-ODAP content. Cooking grass pea like ordinary dal without any soaking or water-discarding leaves most of the toxin intact, which is why prevention starts in the kitchen.

Dietary diversity 🔗

The single biggest risk factor for lathyrism is making Kesari dal the dominant source of calories. Studies suggest that the disease typically develops when grass pea contributes more than 30 to 40 per cent of total caloric intake for three months or more. Mixing it with other pulses such as moong, masoor and arhar, with cereals such as rice or wheat, and with green leafy vegetables both dilutes the toxin and supplies the protective sulphur-containing amino acids that help the body neutralise β-ODAP. A varied plate is, in this case, literally a medicine.

Public health and awareness 🔗

Awareness campaigns in vulnerable districts are critical. Anganwadi workers, ASHA workers and primary health centres can be powerful channels for teaching families about safe preparation, especially during droughts when ration supplies of other pulses fall short. Schools in affected blocks can integrate basic food-safety lessons into health education. Government procurement of pulses at the minimum support price and the strengthening of the Public Distribution System also reduce the need to rely on a single risky crop during hard times.

Beyond the household, the scientific community continues to work on the longer-term solution: making grass pea itself safe. Promoting and distributing certified low-ODAP varieties such as Ratan, Prateek and Mahateora, supporting farmers who grow them, and monitoring β-ODAP levels in market samples are all part of a balanced strategy that protects health without abandoning a crop that climate change may make more important, not less.

What students of public health can take away 🔗

Lathyrism is a textbook example of how nutrition, poverty and policy intersect. The disease is not caused by a virus or a bacterium, but by a poor person’s lack of choice. It cannot be cured by hospitals, only prevented by economic and social change. It teaches that a balanced diet is not a luxury but a shield against silent toxins that even nature places in our food. And it shows that scientific research, from identifying β-ODAP at IISc Bengaluru to breeding safer varieties at IARI, can quietly remove a centuries-old burden from millions of lives.

What do you think? If a single pulse can both save lives during a drought and paralyse the very people it feeds, how should a country decide between banning it outright and investing in safer varieties? And what role can young public health professionals play in carrying simple kitchen knowledge, like soaking and decanting, into villages where lathyrism still hides?

References

1. https://en.wikipedia.org/wiki/Lathyrism
2. https://www.gktoday.in/lathyrism/
3. https://connect.iisc.ac.in/2020/12/neurolathyrism-an-unsolved-mystery/
4. https://en.wikipedia.org/wiki/Neurolathyrism
5. https://www.downtoearth.org.in/food/rumoured-forbidden-it-s-time-to-banish-fears-around-khesari-dal-and-relish-the-nutritious-legume-92976
6. https://crackittoday.com/current-affairs/lathyrism-neurological-disease/
7. https://pubmed.ncbi.nlm.nih.gov/3454610/