A polymer-based preparation (a chitosan-microgel preparation called CHM), intended for use as a diet supplement reducing fat and cholesterol absorption from the digestive tract, was obtained by the combination of chitosan of a reduced molecular weight with a polyvinylpyrrolidone microgel in a I : I (w/w) ratio. Both components were obtained with ionizing radiation (controlled degradation of chitosan in the solid state and crosslinking polymerization of neat vinylpyrrolidone). The chitosan component was shown in previous in vitro studies to exhibit a high fat-binding capacity, whereas the microgels, able to swell to about 40 times their original volume, were intended to serve as stomach-filling agents. The influence of the CHM preparation on the body mass, the weight of the liver and other principal organs, and the serum levels of triglycerides and cholesterol was examined in rats fed a fat- and cholesterol-rich diet (FChD). It was found that the preparation administered as a diet additive at 4% CHM (2% chitosan) in rats effectively prevented body mass gain, fat accumulation in the liver, and liver enlargement, which otherwise developed in the animals fed FChD only, whereas the weight of the other main organs (heart, liver, kidney, spleen, testicles, and lungs) remained unaltered. CHM was also capable of exerting this effect when administered to animals already in an atherosclerotic, overweight condition. No adverse effects were observed during the 10 weeks of feeding the animals the CHM-containing diet. (C) 2007 Wiley Periodicals, Inc.