Chitin is a polysaccharide derived from the shell of crustaceans. Chitosan is a deacylated chitin derivative and ChitoRich™ is a chitosan-based formulation. Chitosan is known to inhibit dietary fat absorption. ChitoRich™ and chitosan were evaluated for their ability to control fat absorption in growing rats. Forty-eight rats (about 150 g) were fed for 4 weeks on 12 different diets containing two levels of vegetable shortening (15 and 5%) and fiber (5 and 2.5%) with cellulose, chitosan, or ChitoRich™ as the dietary fiber sources. Rats fed ChitoRich™ ate less and gained less body weight than rats fed the other fiber sources. Rats fed ChitoRich™ adapted over time; thus, the weight control effect was not significant during the third and fourth weeks. Feed efficiency of the rats fed ChitoRich™ was lower than that seen in rats fed the other fibers, indicating that calories from a higher percent of absorbed macronutrients were required to maintain their bodies. Apparent fat digest (AFD) was lower in rats fed the ChitoRich™ than in the rats fed cellulose. The reduction of AFD was not as great as that seen by other researchers, possibly due to the low solubility and high viscosity of shortening, compared to corn oil. AFD of the rats fed ChitoRich™ increased over time, suggesting an adaptation to ChitoRich&trad;. Apparent protein digestibility (APD), apparent Ca digestibility (ACaD), and weight gain per unit of protein intake were less in the rats fed ChitoRich™ than in the other fiber-fed groups. ChitoRich™-fed rats had retarded body weight gain, reduced levels of serum albumin, total liver lipids, and epididymal fat weight when compared to the other fiber groups, possibly due to the reduced caloric intake, FD, and APD. Serum cholesterol level was not affected by the fiber source. Liver iron and zinc concentrations were not different among fiber sources, indicating that chitosan and ChitoRich™ may not inhibit the absorption of trace minerals. Liver retinol concentration in the ChitoRich™-fed rats was higher than in the cellulose- or chitosan-fed groups, possibly due to the antioxidant effect of ascorbic acid. All rats were free of microscopic lesions, suggesting that chitosan and ChitoRich™ are safe sources of dietary fiber under these dietary conditions. ChitoRich™ is effective for reducing dietary fat absorption and body weight gain.