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Food products are fundamentally mixtures of chemical compounds including carbohydrates, amino acids, fats, oils, and vitamins. Contamination may be caused by either naturally occurring substances or by synthetic chemicals that may be added or are present during agricultural production or post-harvest treatment and further processing.
Because human diets are normally composed of large numbers of different foods, only minute quantities of any specific toxic material are consumed. Thus dilution exerts a significant protective effect against acute intoxication. Toxicants are substances which, upon ingestion, produce changes in homeostasis that are threatening to the normal function of the organism.
A small number of these chemicals, such as the hydrazines found in a few mushrooms, are highly carcinogenic. In general, however, the adverse effects of toxic chemicals in plants are related to interference with nutrient availability, metabolic processes, detoxification mechanisms, and allergic reactions in particular animals and humans. Many natural toxins are found in staple foods of the human diet such as grains and legumes.
There is a difference of degree between toxicity and hazard, and the hazard to man in normal good health from naturally occurring toxicants in food is usually slight, because of (a) the small concentrations and (b) antagonistic interactions between toxicants which provide "safety in numbers." Hazard from foods may indeed exist under some circumstances, such as the presence of abnormal contaminants, ingestion of abnormal amounts, or abnormal susceptibility existing in some disease states. However, the major hazards of the dinner table can ordinarily be ascribed to careless food handling, unbalanced or fad diets, or overeating.
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