Some plants and animals originate food contain toxic substances. Some pulses and legumes contain a number of toxic substances such as protease inhibitors, lathyrogens, and flavism causing agents, cyanogens, haemaglutinins and paponins which are discussed below:

a) Trypsin inhibitor is a proteinous in nature. It suppresses the release of amino acid. It thus interferes with the normal growth of animals fed with such pulses.

b) Haemglutinins are also proteins. They impair the absorption system.

c) Cynogenic glycosides cause cyanide poisoning on hydrolysis of the glycoside by the enzyme α-glucosidase hydrogen cyanide is liberated.
Cyanides content of 10-20 mg per 10 gm of pulses is considered safe.

Many legumes excepting limabean (Phaseolus lunatus) contain cyanide within these limits.

d) Saponins are glycosides of high molecular weight. It has been reported in soyabean, swordbean and jack bean. Toxic saponins cause nausea and vomiting and can be removed by soaking the beans prior to cooking.

e) Alkaloids are known to occur in the seeds of many legumes but they are relatively innocuous.

f) Some compounds present in pulses appear to bind iodine thus producing a state of iodine deficiency in the thyroid and eventually goitre.

g) Lathyrism is a disease that paralyses the lower limbs. The disease is associated with consumption of kesari dal regularly as high as 300g daily.

In lathyrism, the toxic substances interfere with formation of normal collagen fibers in the connective tissue.

h) A hemolytic factor in Vicia faba causes flavism. It is caused by eating broadbeans or by inhaling pollen of its flowers. Flavism is haemolytic anaemia. In several cases, death may occur within 24-48 hours of the onset of the attack.

i) Oxalic acid, a constituent of rhubarb, spinach and beet may cause oxalic poisoning in certain individuals.

j) Some poisonous substances may also be present in some cereals and vegetables e.g. protease inhibitor in cereals and potatoes, saponins in spinach and asparagus and goitrogens in rapeseed mustard, cabbage and related species. Goitrogens cause hypothyroidism and thyroid enlargement.