The great variety of agricultural productions is only one form of the various manifestations of nature. It is a current error today to believe that all that is natural is perfect, and, from a nutritional point of view, devoid of danger. However, numerous examples such as toxic mushrooms and fishes prove the contrary. Protein plants are not an exception to the rule. Although the side effects of some of their componants are not always as severe as those of mycotoxines or ichyotoxines, they nevertheless do exist. The list of noxious compounds present in legume seeds or other plant seeds is rather long. It ranges from cyanogenetic heterosides and toxic amino-acids, liable to lead to death, to the antienzymes, hemagglutinins, antivitamins and flatulence producing substances. Also, included are mineral chelating substances, especially phytic acid, oestrogenic hormones and anti-hormones. Some populations show a genetic sensitivity of food such as beans, leading to the terrible favism syndrome. The existence of pharmacogenetic problems in human nutrition has not been considered enough. In animal nutrition they are of less importance because of the possibilities offered by animal genetics. Clinicians and nutritionists know the existence of these substances. Repeated experiments clearly indicate their more or less marked toxicity. Agricultural and technological means are used to surpass and/or reduce these toxical or pharmacodynamical actions. In many circumstances, re-adjustments of the dietary balances are very useful. Thus, there are antagonisms between biology and the economy of animal production, interrelated with human nutrition. The art of animal production is to reduce if not to suppress these antagonisms without taking into consideration the intelluctual deviations and aberrations of those who are forgetting more and more the imperatives of agriculture, whose adaptation is primordial to prevent the world from dying of starvation.