Chemicals that plants make to ward off pests stimulate nerve cells in ways that may protect the brain against diseases such as Alzheimer's and Parkinson's
Traditional healers learned through trial and sometimes fatal error that these same plants had important medicinal uses. Pharmacologists, toxicologists and biochemists are now confirming that plant chemicals that are toxic when consumed at high levels can be hormetic—that is, they provide health benefits when eaten in smaller amounts.
When the effects of hormesis-inducing substances are measured, they yield what scientists call a biphasic response curve. It can be illustrated on a graph plotting effects relative to dose and by drawing a line that traces an upside-down U shape. The effect line rises at first to indicate that eating a small or moderate amount of a plant chemical has beneficial health effects. It then drops gradually to illustrate the toxicity that emerges as more of these substances are consumed. Eating too many Brazil nuts can poison the liver and lungs because of the presence of the trace element selenium. Yet eating just a few supplies an essential nutrient that is incorporated into an enzyme that may help protect against heart disease and cancer. This example illustrates how hormesis works and differentiates it from homeopathy, which claims, without valid evidence or a plausible mechanism, that vanishingly small amounts of what causes illness can be curative.