Dietary soluble fiber and cholesterol affect serum cholesterol concentration, hepatic portal venous short-chain fatty acid concentrations and fecal sterol excretion in rats.

Sprague-Dawley rats were fed diets containing 7.5% dietary fiber as cellulose (control), pectin, psyllium or oat bran with or without 0.3% added cholesterol for 3 wk. Among rats fed cholesterol, liver total lipid and cholesterol concentrations were significantly lower in groups fed pectin, psyllium and oat bran compared with cellulose-fed controls. Cholesterol feeding resulted in significantly greater liver cholesterol in rats fed cellulose, psyllium and oat bran but not in those fed pectin. Among rats fed cholesterol, total serum cholesterol levels were significantly lower in those fed pectin than in those fed psyllium, oat bran or cellulose. When cholesterol was fed, the oat bran-fed group had significantly higher butyrate and the pectin-fed group had significantly higher propionate concentrations in the hepatic portal vein than did cellulose-fed controls. The groups fed psyllium, oat bran and pectin all had significantly higher fecal neutral sterols than did the cellulose-fed group when cholesterol was fed. Without dietary cholesterol only pectin-fed rats had significantly higher fecal excretion of neutral sterols than those fed cellulose. Dietary fiber did not influence fecal acidic sterol excretion. However, the addition of cholesterol to these fiber diets was accompanied by a significantly higher bile acid excretion than that of animals fed cellulose without cholesterol. The results of this study indicate that soluble dietary fibers may exert their hypocholesterolemic effect by increasing excretion of fecal neutral sterols.     

Soluble dietary fiber and cholesterol influence in vivo hepatic and intestinal cholesterol biosynthesis in rats.

Ninety-six male Sprague-Dawley rats were randomly assigned to eight dietary treatments. Rats were fed, with ad libitum access, diets containing 10% dietary fiber as cellulose (control), pectin, psyllium or oat bran with or without 0.3% added cholesterol for 3 wk. Among cholesterol-fed rats, liver total cholesterol was significantly lower in rats fed diets supplemented with either pectin or psyllium compared with those fed cellulose. In contrast, rats fed oat bran with cholesterol had significantly higher liver cholesterol concentrations compared with cellulose-fed animals. Liver total lipid concentrations were significantly lower in groups fed pectin and psyllium with or without dietary cholesterol compared with cellulose-fed controls. Pectin feeding with or without dietary cholesterol significantly lowered plasma total cholesterol compared with cellulose feeding. Oat bran had no effect on plasma total cholesterol compared with control diets. Hepatic sterol synthesis was significantly greater for animals fed soluble dietary fibers compared with those fed cellulose, but the effect on intestinal sterol synthesis was less pronounced.     

Dietary fructose but not starch is responsible for hyperlipidemia associated with copper deficiency in rats: effect of high-fat diet

OBJECTIVE: To test the hypothesis that copper deficiency in rats may be hyperlipidemic only when the diets consumed contain nutrients which contribute to blood lipids such as fructose and high fat. METHODS: Weanling male Sprague Dawley rats were fed diets which contained either starch or fructose as their sole carbohydrate source. The diets were either inadequate (0.6 microg Cu/g) or adequate (6.0 microg Cu/g) in copper and contained either high (300 g/kg) or low (60 g/kg) fat. At the end of the 4th week the rats were killed. Livers were analyzed for copper content. Plasma was analyzed for cholesterol and triglyceride concentrations. RESULTS: High-fat diet did not increase blood lipids in rats fed a copper-deficient diet containing starch. In contrast, the combination of high-fat diet with fructose increased blood triglycerides and fructose with copper deficiency resulted in a significant increases in blood cholesterol. CONCLUSIONS: Hyperlipidemia of copper deficiency in rats is dependent on synergistic effects between dietary fructose and copper deficiency and fructose and amount of dietary fat. Hyperlipidemia does not develop if starch is the main source of dietary carbohydrate in a copper-deficient diet even if a high-fat diet is fed.     

Hamsters and guinea pigs differ in their plasma lipoprotein cholesterol distribution when fed diets varying in animal protein, soluble fiber, or cholesterol content.

There were two objectives to these studies: 1) to compare the lipoprotein cholesterol distribution in two animal models in response to different dietary treatments and 2) to assess whether the hypercholesterolemia induced by high cholesterol intake could be reversed by consumption of vegetable-protein and/or dietary fiber. Guinea pigs, which carry the majority of plasma cholesterol in LDL, and hamsters, with a higher distribution of cholesterol in HDL, were evaluated in three different studies. In Study 1, animals were fed semi-purified diets for 4 wk with proportions of 60:40, 20:80 or 0:100 (w/w) of casein/ soybean protein. Hamsters and guinea pigs that consumed 100% soybean protein had lower plasma total cholesterol (TC) than those fed diets containing casein (P < 0.01). In Study 2, three doses of dietary pectin (2.7, 5.4, or 10.7 g/100g) added in place of cellulose were tested. Intake of 10.7 g/100 g pectin resulted in the lowest plasma TC concentrations for both species (P < 0.01). Although the TC lowering was similar in studies 1 and 2, the lipoprotein cholesterol distribution differed. Whereas the differences in plasma cholesterol were in LDL in guinea pigs, hamsters exhibited differences in both non-HDL and HDL cholesterol. In study 3, animals were fed 100% soybean protein, 10.7 g/100 g pectin, and three doses of dietary cholesterol: 0.04, 0.08, or 0.16 g/100 g, which is equivalent to 300, 600, or 1,200 mg/d in humans. Guinea pigs and hamsters had the highest plasma LDL and hepatic cholesterol concentrations when they consumed 0.16 g/100 g of cholesterol (P < 0.01). However, intake of 0.08 g/100 g of cholesterol resulted in lower plasma LDL cholesterol concentrations than did consuming high animal protein (60:40 casein/ soy) or low soluble fiber (2.7 g/100 g). Relatively high levels of dietary cholesterol combined with vegetable protein and soluble fiber resulted in desirable lipoprotein profiles in animal models that significantly differ in their lipoprotein cholesterol distribution.     

Effects of tomato pomace and mixed-vegetable pomace on serum and liver cholesterol in rats

The effects of tomato pomace and mixed-vegetable pomace, vegetable processing by-products, on serum and liver cholesterol were compared against pectin, wheat bran, cellulose, and lignin. Male Sprague-Dawley rats (100 g) were fed high sucrose, semi-purified diets containing basal (0), 5% or 10% of the fiber source and either 0, 0.5% cholesterol or 0.5% cholesterol + 0.125% sodium cholate. After 28 days, there were highly significant differences (P less than 0.001) in serum and liver cholesterols due to fiber source, dietary cholesterol and the interaction. The effect of fiber source level was significant (P less than 0.05) for liver cholesterol only. Pectin groups had serum and liver cholesterol levels lower (P less than 0.05) than the others. At the 10% level, tomato pomace, wheat bran and lignin (Indulin AT) groups had serum cholesterols higher (P less than 0.05) than basal; the mixed-vegetable pomace and cellulose groups were not different from basal. Liver cholesterols of tomato pomace, mixed-vegetable pomace, wheat bran and lignin groups were not different at the 10% level, but were higher than the pectin, cellulose and basal groups (P less than 0.05). In a second experiment, serum cholesterols of rats fed pectin were lower (P less than 0.05) than for those fed cellulose or two types of lignin (Indulin AT, Reax 27).     

Effect of pectin,type of fat,and growing rate on lipid metabolism in rats

The effects of pectin, type of fat, and growing rate on lipid metabolism were investigated. Male Wistar rats weighing 122±1 g were fed ad libitum for 8 weeks a nutritionally adequate diet containing 0.5% cholesterol, 12% fat, either corn oil (CO) or beef tallow (BT), and 5% fiber, either cellulose (CE) or pectin (PE). At the end of the feeding period, the rats in each diet group were divided according to their body weight into two groups, slow-growing (range 360 g to 426 g, SG) or fast-growing (range 444 g to 479 g, FG). The difference between the means of the two groups was highly significant (P<0.01). Dietary pectin compared to cellulose lowered liver cholesterol and total liver lipid. However, there was a significant interaction between the type of dietary fiber and the type of dietary fat so that liver total lipid concentration was lower in the BT-fed than in the CO-fed rats. Liver triglyceride level (only measured in the FG group) was not influenced by fiber but was markedly higher in the CO-fed than the BT-fed rats. A significant triple interaction between type of dietary fiber, type of dietary fat, and growth rate was observed for serum cholesterol. Serum cholesterol was significantly lower in the PE-fed than the CE-fed animals except when BT was the dietary fat fed the SG rats and CO was the dietary fat fed the FG rats. The present results suggest that in determining lipid metabolism the interaction between extrinsic factors and intrinsic factors such as growing rate should be taken into consideration.     

Dietary oxidized cholesterol increases expression and activity of antioxidative enzymes and reduces the concentration of glutathione in the liver of rats

An experiment was conducted with rats to investigate the effect of dietary oxidized cholesterol on the antioxidant status. Four groups of male, growing Sprague-Dawley rats received diets containing unoxidized or oxidized cholesterol (5 g/kg diet) with either coconut oil or salmon oil as dietary fat (100 g/kg diet) for 5 weeks. The oxidized cholesterol preparation consisted of 7 g of various cholesterol oxidation products and 93 g of unmodified cholesterol per 100 g preparation. No significant amounts of oxysterols were detected in the unoxidized cholesterol-supplemented diets. As parameters of the antioxidant status activities, mRNA concentrations of several antioxidative enzymes and the concentrations of glutathione were measured. Rats fed the diets containing oxidized cholesterol had significantly higher mRNA concentrations of glutathione peroxidase (p < 0.001) and superoxide dismutase (p < 0.01), a significantly higher activity of glutathione peroxidase (p < 0.001), and significantly lower concentrations of total (p < 0.05) and reduced glutathione (p < 0.01) in the liver than rats fed diets containing unoxidized cholesterol. These effects were independent of the dietary fat. In conclusion, the study suggests that dietary oxidized cholesterol stresses the antioxidant defense system in rats.     

Partially hydrolyzed guar gum increases intestinal absorption of iron in growing rats with iron deficiency anemia

OBJECTIVE: The objective of this study was to evaluate the effect of partially hydrolyzed guar gum (PHGG) dietary fiber towards intestinal iron absorption, for dietary intake and on the growth of rats with iron deficiency anemia in comparison to those fed on a diet with cellulose and without dietary fiber. MATERIALS AND METHODS: Male Wistar rats (n=24) weaned at 21 days were fed with AIN93-G diet without iron for 2 weeks in order to induce iron deficiency anemia. At 36 days old, the anemic rats were divided into three groups: (1) PHGG group-100g of PHGG per kg of diet; (2) Cellulose group-100g of cellulose per kg of diet; (3) Control group-diet without dietary fiber. All the diets had 25mg of elemental iron/kg of diet added to lead to recovery from iron deficiency anemia. RESULTS: The final hemoglobin values in g/dl, for the PHGG group, the cellulose group and the control group were, respectively: 11.3+/-1.2, 8.6+/-0.7 and 8.1+/-0.9 (P<0.001). The levels of hepatic iron, in mug/g of dry tissue, in the same order, were: 322.2+/-66.6, 217.2+/-59.1 and 203.7+/-42.4 (P<0.001). Apparent iron intestinal absorption was, respectively: 67.5+/-8.9%, 35.4+/-15.3% and 31.3+/-24.9% (P<0.001). The three groups consumed similar quantities of diet. The changes in weight and in body length were similar in the three groups studied. CONCLUSION: PHGG led to greater intestinal absorption of iron, regeneration of hemoglobin and hepatic levels of iron than diet with cellulose and diet control.     

Effect of dietary cholesterol and fat levels on lipid peroxidation and the activities of antioxidant enzymes in rats

The aim of this study was to investigate the effect of dietary fat levels, with or without cholesterol, on lipid peroxidation and the activities of antioxidant enzymes in rats. Thirty-two Wistar rats aged 4 weeks were divided into 4 groups and fed high (20%; HF) or low (5%; LF) fat, with or without 1% cholesterol, for 6 weeks. Cholesterol feeding resulted in significantly higher concentrations of serum cholesterol, but lowered serum triacylglycerol levels. Cholesterol feeding also led to markedly decreased levels of hepatic thiobarbituric acid reactive substances (TBARS) and lower activities of hepatic superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase, and glucose-6-phosphate dehydrogenase (G6PDH) when compared with cholesterol-free counterparts in both HF and LF diets. On the other hand, rats fed high-fat diets showed increased serum and liver TBARS, but decreased hepatic GSH-Px, SOD, and G6PDH activities. Hepatic catalase activity was lower in rats fed cholesterol-containing diets, but higher in rats fed high-fat diets, and interaction existed between cholesterol and fat feeding. These results suggested that dietary cholesterol might delay lipid peroxidation and decrease the activities of the hepatic antioxidant enzymes. The degree of lipid peroxidation was also influenced by dietary fat levels.     

Interrelated effects of dietary fiber and fat on lymphatic cholesterol and triglyceride absorption in rats

Lymph cannulated rats were administered intragastrically a test emulsion containing 25 mg of [14C]cholesterol, 50 mg of either guar gum, cellulose or chitosan, and 200 mg of either safflower, high-oleic safflower or palm oil, and the absorption of labeled cholesterol and fatty acids was measured. The type of both dietary fiber (P less than 0.001) and fat (P less than 0.05) significantly influenced cholesterol absorption. A significant interaction of fiber and fat on cholesterol absorption (P less than 0.05) was also observed. Chitosan effectively lowered cholesterol absorption more than did guar gum or cellulose, and this effect was more significant when given with safflower or high-oleic safflower oil than with palm oil. When guar gum was the source of dietary fiber, dietary fats did not modify cholesterol absorption. Dietary fiber also significantly affected triglyceride absorption (P less than 0.05). Absorption tended to be low in the chitosan, high in the cellulose and intermediate in the guar gum group. Absorption of safflower and high-oleic safflower oils tended to be higher than that of palm oil when cellulose or guar gum was fed. Guar gum, as compared with the other fibers, altered the absorption pattern of both cholesterol and triglyceride. The results showed that the type of dietary fat significantly influenced the effect that dietary fiber exerted on lipid absorption.     

Effects of manufactured soluble dietary fiber from Quercus mongolica on hepatic HMG-CoA reductase and lipoprotein lipase activities in epididymal adipose tissue of rats fed high cholesterol diets

This study investigated the effect of a manufactured soluble dietary fiber on lipid metabolism in rats fed high cholesterol diets. Soluble dietary fiber was prepared from wood chips of oak (Quercus mongolica). Male Sprague-Dawley rats weighing 100 +/- 10 g were randomly assigned to either a normal diet or five high cholesterol diets containing 1% cholesterol and different fiber supplements. The high cholesterol groups were subdivided into fiber-free diet (FF), 5% pectin (5P), 10% pectin (10P), 5% manufactured soluble dietary fiber (5QM), and 10% manufactured soluble dietary fiber (10QM) groups. Total serum cholesterol concentrations in all soluble dietary fiber-supplemented groups were lower than in the FF group. The high-density lipoprotein-cholesterol concentration in the FF group was significantly lower, compared with the normal group, but was increased in groups supplemented with soluble dietary fiber. Low-density lipoprotein-cholesterol levels and the atherogenic index had the same tendency as total cholesterol concentration. Compared with the FF group, in the 5P, 5QM, 10P, and 10QM groups hepatic triglyceride concentrations were 12%, 16%, 20%, and 24% lower, respectively, and hepatic cholesterol concentrations were 48%, 52%, 52%, and 58% lower, respectively. Hepatic 3-hydroxy-3-methylglutaryl-CoA reductase activity in the soluble fiber groups was significantly higher than in the FF groups, but lower than the normal group. When hepatic tissue was observed under a light microscope, the FF group had completely formed lipomas in the hepatic tissue, which led to fat deposits and then a fatty liver. The size and number of lipomas were lower in the soluble dietary fiber-fed groups, as compared with the group not fed dietary fiber. In conclusion, improvements in lipid metabolism were observed as a result of the manufactured soluble dietary fiber from the oak chips, and were similar to that seen for pectin. The preparation method for the soluble dietary fiber from oak chips successfully produced a functional soluble fiber.     

Fermentation of resistant rice starch produces propionate reducing serum and hepatic cholesterol in rats

This study was designed to investigate the effects of different proportions of rice starch and cornstarch on lipid metabolism in rats fed high dietary cholesterol. Male Wistar rats were fed a 10 g/100 g fat diet containing 1 g/100 g cholesterol with 0 (control diet), 15, 30, 45 or 63 g/100 g rice starch with an enzyme resistant starch concentration of 1.26, 1.39, 1.52, 1.65 or 1.80 g/100 g, respectively, for 4 wk. Groups fed diets with < 63 g/100 g rice starch were supplemented with cornstarch to 63 g/100 g. The two kinds of starch had different structures as seen using scanning electron microscopy (SEM). The rice starch was an aggregation (n = 20-60) of smaller granules (3-8 microm in diameter), whereas the cornstarch was composed of larger (5-15 microm in diameter), single granules. The compound rice starch (0.99 kg/L) was larger in size and denser in structure than cornstarch (0.63 kg/L). Serum total cholesterol concentrations in rats fed both the 45 and 63 g/100 g rice starch diets were significantly lower than in all other groups (P < 0.05). The serum propionate concentration in the rats fed 63 g/100 g rice starch diets was significantly higher than that of other groups. Hepatic triglyceride and total cholesterol concentrations in rats fed 63 g/100 g rice starch diets were significantly lower than in the control group. These results suggest that, because the compound rice starch was an aggregation of smaller granules, larger in size and denser in structure than cornstarch, it was digested more slowly and altered lipid metabolism. Resistant rice starch may be fermented to produce propionate, which reduces serum and hepatic cholesterol.     

Metabolism of cholesterol is altered in the liver of C3H mice fed fats enriched with different C-18 fatty acids.

We examined whether the degree of saturation of C-18 fatty acids influenced hepatic cholesterol metabolism in C3H mice. The mice were fed diets containing 20 g/100 g fat, enriched in stearic (18:0), oleic (18:1) or linoleic acid (18:2) with or without 1 g/100 g cholesterol. Plasma total cholesterol concentration was lower in mice fed the 18:0 diet relative to those fed the 18:1- or 18:2-enriched diets (P < 0.05) regardless of dietary cholesterol supplementation. Dietary cholesterol significantly raised hepatic total cholesterol concentration (P < 0.05) in those fed the 18:1- and 18:2-enriched diets, but not in mice fed the 18:0-enriched diet. Dietary cholesterol raised biliary cholesterol concentration (P < 0. 05) in mice fed the 18:1- and 18:2-enriched diets, but not in mice fed the 18:0-enriched diet. The cholesterol saturation index was variably affected by the fat diets. Feeding diets containing cholesterol suppressed the hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) activity and induced acyl coenzyme A:cholesterol acyl transferase (ACAT) activity compared with feeding diets without cholesterol (P < 0.05), indicating that the liver was exposed to dietary cholesterol. Hepatic ACAT activity was lower in mice fed the 18:0-enriched diet compared with those fed the 18:1- or 18:2-enriched diets (P < 0.05). Addition of cholesterol to the 18:1 diet induced the largest increase of hepatic ACAT activity, and this was associated with the enrichment of VLDL with cholesterol. Varying the degree of saturation of C-18 fatty acids influences the metabolism and disposition of hepatic cholesterol.     

Neonatal genetically lean and obese pigs respond differently to dietary cholesterol.

The impact of cholesterol exposure in early life on later cholesterol metabolism is not clearly understood. Sixteen newborn genetically lean and obese pigs were fed 0 or 5.0 g cholesterol/kg diet (0 or 0.5%) (liquid diets for 12 d, dry diets thereafter) for 33 d, after which they were all fed 10.0 g cholesterol/kg diet (1.0%) for 23 d. All animals were killed on d 56 and whole-body protein, fat and water were determined on the ground carcass. Dietary cholesterol had no consistent effect on growth rates or body composition. Mean fat content of lean pigs was 15.1% compared with 22.7% for obese pigs; corresponding values were 14.8 and 14.4% for protein and 65.5 and 58.3% for water. Concentrations of plasma total cholesterol, HDL cholesterol and apolipoproteins B and A-1 were increased by 0.5% dietary cholesterol in obese but not in lean piglets, although dietary cholesterol caused HDL and LDL size distribution profiles to shift toward larger-sized components in both strains. Plasma total cholesterol and apolipoprotein B concentrations rose two- to eightfold in all groups after the 1% cholesterol diet was consumed; these changes were accompanied by shifts in LDL and HDL size distribution profiles towards larger-sized components. With 1.0% cholesterol in the diet of all groups, HDL cholesterol concentration increased by approximately 50% in both groups of lean pigs and in obese pigs previously fed cholesterol, but did not increase further in obese pigs previously fed 0.5% cholesterol. The magnitude of the hypercholesterolemic response in lean pigs was blunted by previous exposure to 0.5% dietary cholesterol, but the response was accentuated in obese animals that had been previously exposed to 0.5% dietary cholesterol. These data provide evidence that genetic differences between obese and lean pigs affect their serum lipoprotein responses to high cholesterol intake.     

High protein buckwheat flour suppresses hypercholesterolemia in rats and gallstone formation in mice by hypercholesterolemic diet and body fat in rats because of its low protein digestibility

OBJECTIVE: This study evaluated the physiologic properties of high protein buckwheat flour (PBF) by examining its effects on serum cholesterol and body fat in rats and on cholesterol gallstone formation in mice. METHODS: Animals were fed experimental diets that contained casein, buckwheat protein extract (BWP), or PBF as a protein source (net protein content 200 g/kg). RESULTS: In experiment 1, consumption of PBF and BWP for 10 d caused 33% and 31% decreases, respectively, in serum cholesterol of rats fed cholesterol-enriched diets when compared with consumption of casein (P < 0.05). Dietary PBF caused a significant decrease in liver cholesterol, whereas dietary BWP caused only a slight decrease (P > 0.05). Fecal excretion of neutral and acidic steroids in the PBF group was significantly higher than those in the BWP and casein groups. In experiment 2, consumption of PBF for 10 d significantly suppressed adipose tissue weight and hepatic activity of fatty acid synthase in rats fed cholesterol-free diets compared with consumption of casein (P < 0.05), whereas that of BWP for this period caused only a slight decrease in adipose tissue weight (P > 0.05). In experiment 3, dietary PBF and BWP significantly decreased the incidence of cholesterol gallstones and lithogenic index in mice fed cholesterol-enriched diets for 27 d, which was associated with increased fecal excretion of acidic steroids. CONCLUSION: This study demonstrated that PBF has strong activities against hypercholesterolemia, obesity, and gallstone formation, suggesting a potential usefulness of PBF as functional ingredient.     

Regulation of cholesterol and lipoprotein metabolism in guinea pigs mediated by dietary fat quality and quantity.

The effects of dietary fat quality and quantity on regulation of cholesterol and lipoprotein metabolism were measured in guinea pigs. The animals were fed 7.5 or 15% (wt/wt) fat diets containing either polyunsaturated corn oil (CO), monounsaturated olive oil (OL) or saturated lard as the fat source. Dietary fat quality had a number of significant effects: animals fed the CO-based diet had lower plasma LDL levels and LDL particles of higher density with decreased ratios of core-to-surface components. Apoprotein B/E receptor-mediated binding of LDL to hepatic membranes was twofold higher for animals fed the CO-based diet. Animals fed the OL-based diet had lower hepatic 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity and increased levels of hepatic cholesterol. Hepatic cholesteryl ester levels were lowest for animals fed the lard-based diet. Increasing dietary fat quantity resulted in increased plasma LDL levels and hepatic cholesterol, HMG-CoA reductase activity and receptor affinity for LDL. No changes were observed in LDL binding. These data demonstrate that, independent of dietary fat quantity, CO-based diets lower plasma LDL levels, modify LDL composition and increase hepatic apoprotein B/E receptor number.     

Interrelated effects of the type of dietary fat and carbohydrate on cholesterol metabolism in rats

Rats were fed semipurified diets, differing in the amount of cholesterol and the sources of fat (corn oil or coconut fat) and carbohydrate (sucrose or starch). After 21 days dietary corn oil had induced higher serum cholesterol concentrations than did coconut fat, except for on diets with a high-cholesterol, high-sucrose background. On high-cholesterol diets containing coconut fat, dietary sucrose increased serum cholesterol, when compared with starch; with corn oil sucrose tended to lower serum cholesterol. Such a tendency was not seen on cholesterol-free diets. Cholesterol feeding caused a dramatic increase in liver cholesterol with all dietary carbohydrate-fat combinations. Liver cholesterol was higher in rats fed corn oil than in those fed coconut fat. The influence of the type of dietary carbohydrate on liver cholesterol was dependent on the type of fat and the amount of cholesterol in the diet. Thus effects of a single dietary component on serum and liver cholesterol in rats are strongly influenced by the background of the diet. This implies that published results of experiments on diet and cholesterol metabolism in rats cannot be compared readily.     

Effect of animal and vegetable fats and proteins on distribution of cholesterol in plasma and organs of young growing pigs

Young, growing pigs were fed for 8 wk diets containing either soy protein isolate or ground beef as the main protein source and soybean oil or beef tallow as the main fat source to examine effects of types of dietary protein and fat on cholesterol distribution between blood plasma, plasma lipoproteins and body organs. Type of dietary protein did not influence concentrations of a) cholesterol in plasma, b) low-density-lipoprotein (LDL) cholesterol, c) high-density-lipoprotein (HDL) cholesterol or d) cholesterol in several organs of pigs. Pigs fed tallow had greater concentrations of plasma cholesterol and LDL and HDL cholesterol than did pigs fed soybean oil. Ratios of HDL to LDL were not altered by dietary fat. Cholesterol concentrations were greater in heart, skeletal muscle and viscera of pigs fed soybean oil than in those fed tallow. Plasma cholesterol varied reciprocally with cholesterol in several tissues. Thus, dietary beef and soy protein isolate had similar effects on cholesterol concentrations in plasma, LDL, HDL and organs, whether pigs consumed soybean oil or beef tallow as a major fat source. Soybean oil, however, exerted a hypocholesterolemic effect, irrespective of major source of dietary protein.     

A diet containing alpha-cellulose and fish oil reduces aberrant crypt foci formation and modulates other possible markers for colon cancer risk in azoxymethane-treated rats

There is a need for better understanding of the roles of dietary fats and fibers in colon cancer risk. We examined the effect of different dietary fiber and fat sources on an azoxymethane (AOM)-induced colon cancer in rats. In a 2 x 3 factorial design, rats were fed a semipurified diet containing soy-derived fiber (Fibrim), alpha-cellulose (Solkafloc) or resistant starch (RS; Hi-maize) at 10 g dietary fiber/100 g diet, combined with fish oil (FO) or sunflower seed oil (SSO) at 10 g/100 g diet, and lard added to all diets at 10 g/100 g, to provide a total of 20 g mixed fat/100 g diet. Sprague-Dawley rats (28 d of age) consumed diets for 4 wk and then two doses of AOM (15 mg/kg body) were administered 1 wk apart by subcutaneous injection. Rats were killed after 13 wk of consuming experimental diets. Colons were fixed in formalin and aberrant crypt foci (ACF) were quantified after staining. ACF counts were higher (+66%, P < 0.01) in rats fed SSO and RS, than in those fed alpha-cellulose and FO. Rats fed FO had 19% fewer ACF than those fed SSO (P < 0.05). alpha-Cellulose was associated with the highest cecal butyrate concentration (P < 0.001), the highest beta-glucuronidase specific activity (P < 0.001) and the lowest cecal water cytotoxicity (P < 0.001) relative to soy fiber- and RS-fed rats. There were inverse correlations between the number of ACF and cecal butyrate concentration (r = -0.33, P < 0.05) and between cecal water cytotoxicity and beta-glucuronidase activity (r = -0.70, P < 0.001). The greatest protection was associated with alpha-cellulose as the fiber source and FO as the fat source as measured by colon ACF numbers in rats.     

Effect of dietary methionine on plasma and liver cholesterol concentrations in rats and expression of hepatic genes involved in cholesterol metabolism

Methionine has been shown to increase plasma cholesterol in animals. In the present study, mechanisms were investigated by which methionine could alter cholesterol metabolism. In the first experiment, forty growing rats were fed four casein-based diets differing in methionine content (2.6, 3.5, 4.5 or 6.0 g/kg) for 14 d. In the second experiment, isolated rat hepatocytes were incubated in media supplemented with 50, 100 or 200 micromol/l methionine. Dietary methionine tended to increase plasma homocysteine concentrations in the rats (P=0.058). A weak positive correlation between circulating homocysteine and plasma cholesterol was observed (R2 0.27, P<0.01). Rats fed 3.5 g/kg or more of methionine had higher concentrations of cholesterol in their plasma, in lipoprotein fractions of density (rho; kg/l) 1.0061.063, and in liver than rats fed 2.6 g/kg methionine. Rats fed 6 g/kg methionine had a higher hepatic expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase and cholesterol-7alpha-hydroxylase than rats fed less methionine. The phosphatidylcholine:phosphatidylethanolamine ratio in rat liver increased with rising dietary methionine concentration; the relative mRNA concentrations of phosphatidylethanolamine N-methyltransferase and cystathionine beta-synthase remained unaffected. Hepatocytes incubated in media supplemented with 100 or 200 micromol/l methionine had a higher cholesterol synthesis than hepatocytes incubated in a medium supplemented with 50 micromol/l methionine; the LDL uptake in hepatocytes was independent of the methionine concentration of the medium. In conclusion, the present study suggests that dietary methionine induces hypercholesterolaemia at least in part via an enhanced hepatic cholesterol synthesis.