Gender differences in response to dietary soluble fiber in guinea pigs: effects of pectin, guar gum, and psyllium.

Abstract

Dietary soluble fiber significantly lowers plasma low density lipoprotein (LDL) cholesterol concentrations in humans and animals. In male guinea pigs, alterations in hepatic cholesterol homeostasis induced by dietary fiber in part account for the decrease in plasma LDL levels (Fernandez 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 fiber elicited similar hypocholesterolemic responses in both genders, female guinea pigs were fed diets containing 12.5% pectin (PE), 12.5% guar gum (GG), 7.5% psyllium (PSY), or 12.5% cellulose (control diet). In addition, physiological (0.04%) (LC) or pharmacological (0.25%) (HC) amounts of cholesterol were tested with the fibers to determine whether dietary cholesterol altered the plasma cholesterol response. Significant reductions in plasma cholesterol were observed in females fed LC diets with PE, GG, or PSY (P < 0.01) while the responses to fiber with high cholesterol intake were more moderate. Hepatic cholesterol concentrations were reduced in the LC group (P < 0.001) with increased HMG-CoA reductase and cholesterol 7 alpha-hydroxylase and decreased acyl CoA:cholesterol acyltransferase (ACAT) activities accompanied by a reduction in hepatic cholesterol pools induced by fiber intake. In addition, plasma LDL lowering in animals fed the LC diets was associated with increases in hepatic LDL receptor Bmax values. Effects of fiber on hepatic cholesterol in animals fed HC diets were moderate and hepatic enzymes 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 lowering, depletion of hepatic cholesterol, or alterations in hepatic cholesterol metabolism, although hepatic HMG-CoA reductase and ACAT activities were lower in females compared to males (P < 0.01). In contrast, females fed the control HC diet had higher plasma LDL levels than males and dietary fiber did not reduce hepatic cholesterol concentrations nor alter hepatic enzyme activities as effectively as in males. These studies demonstrate that female, compared to male, guinea pigs are more responsive to a dietary cholesterol challenge and, that with this pharmacological perturbation, fiber effects are moderate compared to males. In contrast, with low cholesterol intakes, the cholesterol lowering effects of fiber are similar in both genders.