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.
Highlights
Dietary soluble fiber significantly lowers plasma low density lipoprotein (LDL) cholesterol concentrations in humans and animals
Plasma total cholesterol levels were significantly reduced by dietary fiber in female guinea pigs fed low cholesterol (LC) diets (P < 0.01) and dietary cholesterol significantly increased plasma cholesterol levels in the four dietary treatment groups (Table l).No differences in plasma cholesterol, as determined by one-wayANOVA, were observed between the Fmanda et al Dietary fiber, gender, and cholesterolmetabolhm 2193
The hypocholesterolemiceffects of dietary fiber, and the mechanisms involved, vary depending on the type of fiber fed, the species under investigation, and the level of dietary cholesterol [34,35,36,37,38].Rats, for example, are known to be relativelyresistant to dietarycholesterol effects on plasma and hepatic cholesterol concentrations [34,35]while other animal models such as hamsters and guinea pigs are more susceptible to the effects of high dietary cholesterol and respond by increasing plasma cholesterol levels and suppressing hepatic LDL receptors [36,37]
Summary
High intakes of cholesterol [8]. Interestingly, psyllium had similar hypocholesterolemic responses in the Materials guinea pig with either low or high cholesterol diets [9]. Whether female guinea pigs have different responses to (w/w) psyllium plus 5% (w/w) cellulose (PSY).The fatty soluble fiber compared with male guinea pigs and acid composition of palm oil was: C16:O 43.3%, C18:O whether the mechanisms of plasma LDL lowering in 4.1%, C18:139.8%, C18:2 9.7% and fat represented 35%. Pooled LDL samples from each dietary group were iodinated by the method of Goldstein, Basu, and Brown [28] for measurement of LDL binding to hepatic membranes from female guinea pigs fed the homologous diet. Two-way ANOVA (GBSTAT, Silver Spring, MD) was used to test significant effects on plasma lipids, VLDL and LDL composition, hepatic cholesterol, apoB/E receptor B-, and affinity K d , and activities of hepatic HMGCoA reductase, ACAT, and cholesterol 7a-hydroxylase mediated by fiber and cholesterol in female guinea pigs. Linear and power relationships were used to identify significant correlations between measurements (P< 0.05)
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