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CSIRO (Australia) Division of Human Nutrition, Glenthorne Laboratory, O'Halloran Hill, SA 5158, Australia
Plasma cholesterol concentrations were significantly lower in rats fed a cholesterol-free diet containing white wheat flour than those fed the diet with whole wheat or wheat bran. Concentrations of total bile acids and neutral sterols in cecal digesta were significantly higher in rats fed wheat flour than in those fed whole wheat, wheat pollard or wheat bran. Digesta bile acids and neutral sterol pools correlated negatively with plasma cholesterol, indicating that excretion was regulating plasma concentration. Total cecal volatile fatty acid (VFA) concentrations were unaffected by diet but cecal propionate was higher and butyrate lower in rats fed wheat flour than in those fed whole wheat. Cecal digesta butyrate concentrations correlated negatively with the cholesterol metabolite, coprostanol, and with secondary bile acids. Cecal propionate correlated negatively with plasma cholesterol concentration, but butyrate correlated equally positively, suggesting these VFA were indicators rather than regulators of altered cecal steroid metabolism. Effects of white wheat flour on steroid metabolism and cecal VFA resemble those of oat bran and support the observation that wheat flour might be hypocholesterolemic in humans.
KEY WORDS: rats wheat fractions steroid metabolism volatile fatty acids bile acids
1 Presented in part at the Annual Meeting of the Federation of American Societies for Experimental Biology, April 1992, Anaheim, CA [Illman, R. J., Storer, G. B. & Topping, D. L. (1992) White wheat flour lowers plasma cholesterol relative to whole wheat flour in the rat.] and at the 4th Vahouny Fiber Conference, April 1992, Washington, DC [Topping, D. L. Propionate as mediator of the effects of dietary fiber. In: Dietary Fiber (Kritchevksy, D. & Bonfield, C., eds.). Plenum Press, New York, NY and London, U.K. (in press)
2 The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.
3 To whom correspondence should be addressed.
Manuscript received 5 October 1992. Revision accepted 27 January 1993.
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