EFFECT OF DIETARY RHUBARB STALK FIBER ON THE BIOAVAILABILITY OF CALCIUM IN RATS

Ground rhubarb stalk fiber containing, on a dry weight basis, 74% tota l dietary fiber (66% insoluble and 8% soluble) was prepared from rhuba rb plants. This fiber source has been shown to have a pronounced lipid lowering effect in mice. Its high oxalic acid content may, however, b e a limiting factor for its use. The present study was undertaken to d etermine the safe dose level of the fiber in terms of its effect on ca lcium bioavailability. Male weanling Sprague-Dawley rats were fed a se mipurified diet (AIN 76) for 4 weeks containing 0, 1, 3, or 5% rhubarb fiber, or pure oxalic acid equivalent to 5% rhubarb fiber. The fiber content of each diet was brought to 5% by adding cellulose, and the ca lcium level of all diets was the same. As the rhubarb stalk fiber cont ent of the diet increased, a consistent trend of increasing total rete ntion and apparent absorption of calcium was manifested. In contrast, however, cellulose, due to its increased effect on intestinal motility , resulted in a decreased calcium bioavailability. Overall results sug gest that an addition of rhubarb stalk powder up to the level of 5% in a diet does not have detrimental effect on calcium bioavailability.