Effect of baked beans (Phaseoh vulgaris) on steroid metabolism and non-starch polysaccharide output of hypercholesterolaemic pigs with or without an ileo-rectal anastomosis

Abstract

The plasma-cholesterol-lowering effects of some dietary legumes are now well established from animal and human studies, but the mechanism is not completely understood. The present study investigated the effect of baked beans (Phaseolus vulgaris) on steroid metabolism of hypercholesterolaemic pigs. Three groups of four pigs were studied: baseline (BL), normal pigs (NP) and those previously prepared with an ileo-rectal anastomosis to nullify the function of the large intestine (IR). All three groups were given a semi-purified control diet, with about 40% energy as fat (polyunsaturated: saturated fatty acid (P:S) ratio 0.3), supplemented with 10 g cholesterol/kg, for 14 d. Then IR and NP pigs were fed for 28 d on a diet supplemented with 10 g cholesterol/kg and 300 g baked beans/kg (dry-matter basis), so that the 40% contribution to energy from fat was maintained (P:S ratio 0.3). Group BL was fed on the control diet throughout. The intact pigs (NP) fed on baked beans showed considerable differences compared with the other groups, as follows: (a) reduced plasma cholesterol (NS); (b) higher concentration of cholesterol in bile (NS); (c) higher concentration of bile acids, especially secondary bile acids, in bile (P< 0.05); (d) reduced elimination of bile acids in faeces, especially secondary bile acids (P< 0.05); (e) higher excretion of coprostanol and lower elimination of cholesterol in faeces (P< 0.05). From these findings it is proposed that a baked-bean-enriched diet potentiates bacterial fermentation and steroid degradation in the large intestine and enhances conservation of bile acids and cholesterol within the enterohepatic circulation. The high concentration of bile acids and cholesterol in bile may thus promote feedback inhibition of hepatic cholesterol synthesis, and hence, reduce plasma cholesterol.