1. Sterol metabolism was studied in rats fed on a semi-synthetic fibre-free diet and in rats fed on diets containing cellulose (200 or 100 g/kg) or sugar-cane fibre (bagasse) at the same levels.
2. Rats fed on the diets containing cellulose or bagasse produced significantly greater quantities of faeces than did rats fed on the fibre-free diet.
3. Rats given bagasse excreted more bile acid and more neutral sterol in their faeces than did rats fed on cellulose or on the fibre-free diet.
4. After 28 d, hepatic synthesis of cholesterol (from acetate) and cholesterol 7α-hydroxylase activity were significantly higher in animals fed on bagasse than in animals fed on the other two diets.
5. No significant differences in serum cholesterol levels were seen in rats fed on any of the three diets.
6. Food consumption was not substantially altered by the inclusion of bagasse or cellulose in the diets, although the efficiency of foodstuff utilization was generally lower.
7. Bagasse adsorbed substantial quantities of cholic acid in vitro, whereas cellulose did not. The lignin fraction prepared from bagasse contributed only slightly to the total bile acid-binding capacity of bagasse.
8. The results are discussed in the light of possible effects of dietary fibre on sterol metabolism in man.