Natural plant toxins and anti-nutrients
Plants are chemical factories. Unlike animals-- having the luxury of teeth and claws and legs to help them get out of a tight spot-- plants spend their lives in one place and have evolved to rely upon elaborate chemical defenses to ward off unwanted predators. For this reason, plants have in their arsenal an amazing array of thousands of chemicals noxious or toxic to bacteria, fungi, insects, herbivores, and yes, even humans. Fortunately for us, this chemical diversity also includes many compounds that are beneficial to humans-vitamins, nutrients, antioxidants, anti-carcinogens, and many compounds with medicinal value.
Most plant species in the world are not edible, many because of the toxins they produce. The process of domestication has gradually reduced the levels of these compounds over the millennia so that the plant foods we eat today are far less toxic than their wild relatives. Because many of these toxins evolved as a way to fight off predators, not surprisingly, our modern food plants are much more susceptible to disease.
The table below lists a few families of the more common plant toxins found at very low levels in the foods we eat. Many of these compounds are known carcinogens. Some fat-soluble plant toxins even bioaccumulate-- that is, when an animal eats the plant, the toxins collect in animal tissues and pass to humans when we eat the animal-- and can be secreted in human and animal milk (for example, solanine from potatoes). Toxin concentrations in a plant can vary tremendously, often by 100X or more, and can be dramatically affected by environmental stress on the plant (drought, heat/cold, mineral deficiencies, etc) and disease. Different varieties of the same plant species can also have different levels of toxins and nutritional value.
http://www.geo-pie.cornell.edu/issues/toxins.htmlNicola
