Seed lectins : the effects of dietary Phaseolus vulgaris lectins on the general metabolism of monogastric animals
Rats, mice, pigs, quails, chickens, steers and even some insects are unable to grow properly and in some cases die when fed on diets containing raw kidney bean (Phaseolus vulgaris). Although this problem has been extensively studied the precise mechanism of the interference of dietary antinutritional factors with the growth and health of these animals or insects is still not completely understood. In the present work, the toxic effects of the purified kidney bean globulin lectins upon the general metabolism of the rats were studied. The results of the experiments indicated that both qualitatively and quantitatively most of the deleterious effects of raw kidney bean feeding to rats could be accounted for by the inclusion of the pure lectin into nutritionally adequate semi-synthetic diets based on high-quality proteins such as egg albumin. These effects included: (a) a drastic depletion of storage lipid and glycogen and loss of body protein. (The rate of the catabolism of lipids was considerably higher than that of any other body constituent.); (b) a large loss of skeletal muscle (indicated by the change of muscle mass and atrophy of gastrocnemius and plantaris muscles); (c) enlargement of the small intestine, liver and pancreas and involution of the thymus; (d) increased excretion of faecal and urinary nitrogen with a consequently poor nitrogen retention; (e) increased 3-hydroxybutyrate output, and (f) changes in blood concentrations of pancreatic hormones. The magnitude of most of these effects was dependent upon the dietary concentrations of kidney bean globulin lectins (PHA). Thus the extent of the depletion of body lipid and glycogen, loss of muscle, enlargement of the small intestine, liver and pancreas, the extent of the thymus atrophy as well as the increased faecal and urinary nitrogen and increased urinary 3-hydroxybutyrate outputs were shown to be directly correlated with the dietary PHA concentration. In contrast to the deleterious effects of fully active, native PHA, the aggregated lectin preparation (UPHA) did not cause any significant antinutritional effects. The overall results indicated that raw kidney bean is toxic mainly because of its lectin constituent and that local (gut) and systemic adverse reactions caused by PHA account for most of the deleterious effects of this potentially important source of dietary protein for animals and humans.