GENDER DIFFERENCES IN RESPONSE TO DIETARY SOLUBLE FIBER IN GUINEA-PIGS - EFFECTS OF PECTIN, GUAR GUM, AND PSYLLIUM

Dietary soluble fiber significantly lowers plasma low density lipoprot ein (LDL) cholesterol concentrations in humans and animals. In male gu inea pigs, alterations in hepatic cholesterol homeostasis induced by d ietary fiber in part account for the decrease in plasma LDL levels (Fe rnandez et al. 1994. Am. J. Clin. Nutr. 59: 869-878; 1995. 61: 127-134 , and J. Lipid Res. 1995. 36: 1128-1138). To test whether dietary fibe r elicited similar hypocholesterolemic responses in both genders, fema le guinea pig were fed diets containing 12.5% pectin (PE), 12.5% guar gum (GG), 7.5% psyllium (PSY), or 12.5% cellulose (control diet). In a ddition, physiological (0.04%) (LC) or pharmacological (0.25%) (HC) am ounts of cholesterol were tested with the fibers to determine whether dietary cholesterol altered the plasma cholesterol response. Significa nt reductions in plasma cholesterol were observed in females fed LC di ets with PE, CG, or PSY (P < 0.01) while the responses to fiber with h igh cholesterol intake were more moderate. Hepatic cholesterol concent rations were reduced in the LC group (P < 0.001) with increased HMG-Co A reductase and cholesterol 7 alpha-hydroxylase and decreased acyl CoA :cholesterol acyltransferase (ACAT) activities accompanied by a reduct ion in hepatic cholesterol pools induced by fiber intake. In addition, plasma LDL lowering in animals fed the LC diets was associated with i ncreases in hepatic LDL receptor B-max values. Effects of fiber on hep atic cholesterol in animals fed HC diets were moderate and hepatic enz ymes were not altered to the same extent as in the LC groups. For the LC groups there was no gender effect on the magnitude of plasma LDL lo wering, depletion of hepatic cholesterol, or alterations in hepatic ch olesterol metabolism, although hepatic HMG-CoA reductase and ACAT acti vities were lower in females compared to males (P < 0.01). In contrast , females fed the control HC diet had higher plasma LDL levels than ma les and dietary fiber did not reduce hepatic cholesterol concentration s nor alter hepatic enzyme activities as effectively as in males. Thes e studies demonstrate that female, compared to male, guinea pigs are m ore responsive to a dietary cholesterol challenge and, that with this pharmacological perturbation, fiber effects are moderate compared to m ales. In contrast, with low cholesterol intakes, the cholesterol lower ing effects of fiber are similar in both genders.