Tomatoes contain the steroidal glycoalkaloid tomatine, which has been reported to form strong, insoluble complexes with cholesterol in vitro. To determine whether tomatine can reduce dietary cholesterol absorption and plasma levels of cholesterol and triglycerides, we fed hamsters a high-fat, high-cholesterol diet with 0.05-0.2% added tomatine in the diet. The tomatine diets induced lowering of serum low-density lipoprotein (LDL) without changing high-density lipoprotein (HDL) cholesterol. Compared to the control diets, four- to fivefold more labeled dietary cholesterol and coprostanol was excreted in the feces of the tomatine-fed hamsters. The amount of cholesterol excreted in the feces corresponded to the amount of tomatine in the diet. These observations suggest that due to the formation of an insoluble tomatine-cholesterol complex and its excretion in the feces, very little dietary tomatine is absorbed from the digestive tract into the blood stream. They are also consistent with the reported low oral toxicity of tomatine compared to other glycoalkaloids.