Foods, mainly those of plant origin and mushrooms, contain natural toxic substances. Their acute toxicity is as a rule mild, but carcinogenic and teratogenic effects cannot be ruled out. They include e.g. cyanogens, lathyrogens, hydrazines, glucosinolates and related goitrogens, cumarins, saponins, alkaloids and glycoalkaloids, biogenic amines, enzyme inhibitors, such as lectins (haemagglutinins) and trypsin inhibitors and chelating substance e.g. phytates and oxalates. These toxic substances are partly removed by technological processes. When principles of a varied diet are respected, the health risk is reduced to a minimum.