Four groups of weanling male rats were fed either palm, hardened or unhardened soybean oils or cacao butter, for 28d. Comparative studies were made on cholesterol and its metabolites in several tissues and feces from the rats, and on the chemical and physical properties of the dietary fats.
1) Hardening of soybean oil caused increase in octadecenoic acid, including trans-isomers, by conversion from linoleic and linolenic acids, regardless of the bound position in triglyceride. Amounts of saturated fatty acids, situated at the 2-position of triglyceride, were much less in cacaco butter than in palm oil. Cacao butter was mainly comprised of 2-oleo-1, 3-disaturated glycerides, thus causing it to show unique melting behavior.
2) Cholesterol concentrations in serum and liver were low in the hardened soybean oil group, but no significant differences between the cacao butter and palm or soybean oil groups could be detected. This was also observed for serum triglyceride and phospholipid. Analytical results on fatty acids in liver and fecal lipids suggested preferential excretion into the feces of octadecenoic acid, probably its trans-isomers, in the hardened soybean oil group, stearic acid in the cacao butter group, and palmitic acid in the palm oil group.
3) The amounts of cholesterol and its metabolites in feces from the hardened soybean oil group were essentially the same as those in the palm oil group. In the cacao butter group, however, cholesterol content was much higher than that in the palm oil group. Some metabolites subjected to the action of intestinal bacteria, such as coprostanol, lithocholic and deoxycholic acids, were present at significantly lower amounts than those in the other groups. Thus, the ratio of 21 metabolites to cholesterol in the feces was basically the same in all groups, except for the cacao butter group showing a smaller value.
4) From these results, the effects of hardened soybean oil on cholesterol metabolism may be equivalent to those of palm and soybean oils, but cacao butter may somewhat differently affect the metabolism and action of intestinal bacteria.