The effect of pectin on the utilization of marginal levels of dietary protein by weanling rats.

The effect of dietary pectin levels on protein utilization was studied in weanling rats. Levels of 0, 4.8, 16.7 and 28.6% pectin were used in diets containing 10% protein from casein, bread or bread supplemented with lysine or lysine and threonine. Food intake, energy digestibility and protein digestibility were lowered by dietary pectin, resulting in very strong decreases in digestible energy and digestible protein intakes, protein being affected relatively more than energy. The weight gain of the experimental animals was also incrementally inhibited, with a net loss of weight occurring at the 28.6% pectin level. At this level of pectin addition, the mortality of the experimental groups averaged 50%, death occurring within the first 2 weeks of feeding the experimental diets. Dietary pectin worsened the animal's feed conversion and affected negatively the efficiency with which dietary protein was utilized for growth as measured by the net protein ratio, this effect being much more severe for the higher quality protein diets. It seems to have brought the animals' net protein utilization (NPUs) toward intermediate values, increasing the NPUs of the groups fed the bread-based diets and diminishing those of the other protein groups. The cause of these effects is not clear, although they may be due in part to a lower ratio of digestible protein to digestible energy with increasing dietary pectin. Other participating mechanisms may be the development of adverse intestinal microflora or binding of some essential amino acids to a greater extent than others.