Magnesium deficiency affects plasma lipoprotein composition in rats

Weanling rats were pair-fed for 8 d with control and Mg-deficient diets containing 960 and 30 mg of Mg/kg, respectively. The marked reduction in plasma Mg levels indicated that the rats fed the Mg-deficient diet were indeed deficient. In the Mg-deficient rats the percent composition of triglycerides in VLDL, LDL and HDL was elevated and that of protein was reduced. Although the proportion of cholesterol was reduced in LDL and HDL, that of phospholipid was decreased only in HDL. Magnesium deficiency induced a decrease in the percent composition of apolipoprotein (apo) E and a relative increase in the apo C for VLDL. In HDL from Mg-deficient rats, the proportion of apo AI was higher than normal, apo AIV was lower than normal and apo E was virtually absent. The percent composition of oleic and linoleic acids was increased but that of stearic and arachidonic acids was depressed in both VLDL and HDL derived from Mg-deficient rats compared with pair-fed controls. Whether these alterations in lipoprotein profile contribute to hyperlipoproteinemia or are the results of the metabolic changes that produce hyperlipoproteinemia remain to be determined.     

Effect of dietary fat source on lipoprotein composition and plasma lipid concentrations in pigs

Most studies of the effects of dietary fat sources on plasma lipid components have used diets with extreme fat compositions; the current study was designed to more nearly mimic human dietary fat intake. Young growing pigs were fed diets containing either 20 or 40% of energy as soy oil, beef tallow or a 50/50 blend of soy oil and tallow. Different dietary fats did not affect concentrations of cholesterol, triacylglycerol or protein in plasma or major lipoprotein fractions. The concentration of phospholipid was less in plasma and in very low density lipoproteins with soy oil feeding than with tallow feeding. The weight percentage of cholesteryl ester in the low density lipoprotein fraction tended to be greater with 40% than with 20% tallow and tended to be less with 40% than with 20% soy oil. Phospholipid as a weight percentage of low density lipoprotein was least in pigs fed soy oil. Tallow feeding increased the percentage of myristic, palmitic, palmitoleic and oleic acids in plasma, relative to both other groups. Soy oil feeding increased the percentage of linoleic and linolenic acids. These moderate diets were not hypercholesterolemic, but they did alter plasma fatty acid composition and phospholipid concentrations in plasma and very low density lipoprotein.     

Effects of dietary fibers on nonfasting plasma lipoprotein and apolipoprotein levels in rats.

This study was undertaken to determine whether selected dietary fibers had an effect on plasma lipoproteins, apolipoproteins and enzymes involved in cholesterol metabolism in rats. Each experimental diet contained 8% dietary fiber by weight; all animals were killed in a nonfasted state. After 4 wk, final body weight and liver cholesterol were similar in fiber-free controls and in rats fed diets containing cellulose, pectin, oat bran or wheat bran. Pectin-fed animals has significantly lower plasma cholesterol, HDL-cholesterol and apolipoprotein A-I levels, and exhibited significantly higher hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity than did the fiber-free control group. In addition, plasma triglyceride concentrations were lowest in pectin-fed animals. These multiple effects on lipid metabolism were not observed when oat bran, containing one-third soluble fiber, was used. Although total plasma cholesterol levels in wheat bran-fed animals were not different from those in the fiber-free controls or the cellulose-oat bran-fed animals, the LDL cholesterol level was significantly higher than in fiber-free controls or pectin-fed animals. This study demonstrate that dietary fibers included in the diet of rats are able to alter nonfasting lipoprotein cholesterol and apolipoproteins and that pectin, a soluble fiber, was most effective in lowering plasma cholesterol levels.     

Effect of palm oil on plasma lipoprotein concentrations and plasma low-density lipoprotein composition in non-human primates

Palm oil (PO) contains ~43% of palmitic acid. It is the most abundant saturated fatty acid in the diet and it is generally considered the primary cholesterol (C)-raising fatty acid. However, the effect of palmitic acid on plasma cholesterol appears to depend on the cholesterol content of the diet. The aim of this study was to determine the effect of PO with either a high-fat, high-C or moderate-fat, moderate-C diet on lipoprotein C and low-density lipoprotein (LDL) composition. Fifty adult, male vervet monkeys were randomly assigned to the high-fat diet group (HFD: 35%E fat, ~0.106 mg C/kJ; n =20) and the moderate-fat diet group (MFD: 30%E fat, ~0.027 mg C/kJ; n =30). Baseline LDL-C, high-density lipoprotein (HDL)-C and body weight were used to stratify the vervets into comparable experimental groups within each dietary group. The HFD group was divided into two groups of 10 each: one group continued with the HFD in which 8.1%E was derived from lard (AF); in the other group, AF was substituted isocalorically with PO. The MFD group was divided into three groups of 10 each: one group continued with the MFD in which 11.8%E was derived from AF; in the other two groups, the AF was substituted isocalorically with either sunflower oil (SO) or PO. This article presents preliminary results on plasma lipoproteins and LDL composition after 6 months of dietary intervention. Plasma total and LDL-C was higher in all the groups, but the mean changes elicited by PO with either the HFD or MFD were no different from that observed with AF and SO. There was no difference in the mean change of LDL molecular weight within the HFD and MFD. It is concluded that PO is no different from AF (HFD and MFD) or SO (MFD) in its cholesterolaemic effect.     

Effect of dietary seal and fish oils on triacylglycerol metabolism in rats

Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were distributed mainly in the sn-1 and 3 positions of seal oil triacylglycerol and in the sn-2 position of fish oil triacylglycerol. Seal oil or fish oil-rich fats having constant polyunsaturated/monounsaturated/saturated fatty acids and n-6/n-3 polyunsaturated fatty acid (PUFA) ratios were fed to rats for 3 wk. Control rats were fed on a fat containing linoleic acid as the sole PUFA. Seal oil more effectively lowered serum and liver triacylglycerol concentrations than fish oil. The activities of fatty acid synthase (FAS), glucose-6-phosphate dehydrogenase (G6PDH) and hepatic triacylglycerol lipase (HTGL) were significantly lower in the seal oil group than in the control group, whereas the activity of HTGL was significantly lower and the hepatic peroxisomal beta-oxidation and activity of lipoprotein lipase (LPL) in adipose tissue were significantly higher in the fish oil group than in the control group. These observations suggest that the predominant hypotriacylglycerolemic effect of seal oil is caused by the suppression of fatty acid synthesis.     

Interrelationship of plasma triglycerides and HDL size and composition in rats fed different dietary saturated fats

We investigated the relative effects of different dietary saturated fats on the size distribution, apolipoprotein (apo) and chemical composition of HDL in fasted rats. Male Sprague-Dawley rats (174 +/- 2 g) were fed diets containing 0.035% cholesterol and 16% fat (wt/wt) from corn oil (CO diet) or from 2% CO plus 14% butterfat (BF diet), beef tallow (BT diet), palm oil (PO diet) or coconut oil (CN diet) for 6 wk. Apparent lipid digestibility was significantly lower with the PO and BT diets vs. the CO, BF and CN diets. Plasma total cholesterol levels were significantly higher in rats fed the PO and BT diets than in rats fed the BF and CN diets but were not different among the PO-, BT- and CO-fed groups. Nondenaturing gradient gel electrophoresis immunoblot analysis indicated that HDL apo A-I and E resided on particles with significantly smaller modal diameters in rats fed all saturated fats compared with those fed the CO diet. Chemical analyses indicated that HDL generally contained proportionately less protein and more triglyceride, free cholesterol and apo E with saturated fat feeding than with CO diet feeding. Significantly higher plasma and VLDL triglyceride levels were noted with ingestion of the BT, PO or CN diet than with the CO diet. Butterfat feeding resulted in lower plasma triglycerides and HDL-esterified cholesterol than did feeding the other saturated fats. Very low density lipoprotein triglyceride concentrations were inversely correlated with HDL modal diameter of apo E containing lipoproteins (P less than 0.005). These data provide further evidence of the interrelationship of triglyceride and HDL metabolism and suggest that mechanisms independent of cholesterol ester transfer protein may mediate this response in rats.     

Effects of dietary fatty acids on the composition and oxidizability of low-density lipoprotein

OBJECTIVE: The objective of this study was to compare the effects of dietary monounsaturated fatty acids (MUFA), n-6 and n-3 polyunsaturated fatty acids (PUFA) on LDL composition and oxidizability. DESIGN, SETTING AND SUBJECTS: Sixty-nine healthy young volunteers, students at a nearby college, were included. Six subjects withdrew because of intercurrent illness and five withdrew because they were unable to comply with the dietary regimen. INTERVENTIONS: The participants received a 2-week wash-in diet rich in saturated fatty acids (SFA) followed by diets rich in refined olive oil, rapeseed oil or sunflower oil for 4 weeks. Intakes of vitamin E and other antioxidants did not differ significantly between the diets. RESULTS: At the end of the study, LDL oxidizability was lowest in the olive oil group (lag time: 72.6 min), intermediate in the rapeseed oil group (68.2 min) and highest in the sunflower oil group (60.4 min, P<0.05 for comparison of all three groups). Despite wide variations in SFA intake, the SFA content of LDL was not statistically different between the four diets (25.8-28.5% of LDL fatty acids). By contrast, the PUFA (43.5%-60.5% of LDL fatty acids) and MUFA content of LDL (13.7-29.1% of LDL fatty acids) showed a wider variability dependent on diet. CONCLUSIONS: Enrichment of LDL with MUFA reduces LDL susceptibility to oxidation. As seen on the rapeseed oil diet this effect is independent of a displacement of higher unsaturated fatty acids from LDL. Evidence from this diet also suggests that highly unsaturated n-3 fatty acids in moderate amounts do not increase LDL oxidizability when provided in the context of a diet rich in MUFA.     

Copper deficiency alters plasma pool size, percent composition and concentration of lipoprotein components in rats.

Forty weanling male Sprague rats were randomly assigned to two dietary treatments, copper-deficient (9.0 mumol/kg diet) and copper-adequate (102.2 mumol/kg diet). After 7 wk of treatment, reductions in body weight and hematocrit, and an increase in relative heart weight, were observed in the copper-deficient rats. Plasma VLDL, LDL and HDL were isolated by ultracentrifugation and Sepharose column chromatography. In copper-deficient rats, the percent composition of protein was reduced by one-half, and triglyceride was increased by 1.6- and 2.7-fold in LDL and VLDL fractions, respectively. In VLDL, the marked increase in triglyceride was compensated by at least a 75% decrease in percent composition of cholesterol and phospholipids as a result of copper deficiency. No treatment difference in percent composition of HDL components was detected. When the data were expressed as the amount present in the vascular pool corrected for body weight, the plasma pool size of protein, triglyceride, phospholipid and cholesterol of LDL and HDL were increased twofold or more by copper deficiency. In VLDL, a sixfold increase in triglyceride, a 36% reduction in cholesterol, and no change in phospholipid and protein pool size were observed in copper-deficient rats. These data suggest that copper deficiency may enlarge the particle size but not particle number of VLDL, increase both particle size and number of LDL, and elevate particle number but not size of HDL.     

Effects of diets rich in fermentable carbohydrates on plasma lipoprotein levels and on lipoprotein catabolism in rats

This study was conducted to examine the effects of a combination of several dietary fibers (5% guar gum, 5% apple pectin, 15% wheat bran, 22% soybean fiber) and crude potato starch (23%) on plasma lipids and lipoproteins and on liver lipid concentration in rats fed a diet containing either 15% lard or 5% oil with or without dietary cholesterol/cholic acid. Male Wistar rats ate the test diets for 3 wk. The incorporation of fiber and crude potato starch into the diet resulted in a significant enlargement of the cecum; it also increased the concentration of volatile fatty acids and the pool of acetate, propionate and butyrate. Feeding this fermentable carbohydrate decreased plasma cholesterol and triglyceride levels in rats given a low fat diet and prevented the expected rise in plasma cholesterol and triglycerides in rats fed cholesterol/cholic acid or lard. Further studies of high density lipoprotein (HDL) composition, 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMG-CoA reductase) activity and 125I-labeled human low density lipoprotein (LDL) turnover were done in the group fed the low fat diet without added cholesterol/cholic acid. The study of the HDL fraction in rats fed a diet rich in fermentable carbohydrates demonstrated a decrease in the HDL1 subpopulation and in the proportion of apolipoprotein E. Plasma clearance of intravenously injected 125I-labeled LDL was faster in rats fed this diet than in rats fed the fiber-free diet. In the liver, cholesterol and triglyceride levels were depressed whereas the activity of HMG-CoA reductase was increased.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute effects of dietary fat composition on postprandial plasma bile acid and cholecystokinin concentrations in healthy premenopausal women

Bile acids derived from intestinal bacterial metabolism and transported to the breast in plasma may influence risk of breast cancer. The purpose of the present study was to test the hypothesis that fatty acid chain length and degree of unsaturation differ with regard to their influence on the postprandial release of cholecystokinin (CCK) and the subsequent increase in plasma bile acid concentrations that occur following a meal. A randomized crossover design was used to compare five high-fat test meals (50 g fat) with a low-fat test meal (15 g) on plasma bile acid and CCK concentrations in eighteen healthy premenopausal women. The high-fat meals were enriched in oleate or palmitate, or linoleate or medium-chain triacylglycerols (MCT) or a blend of oleate and long-chain n-3 fatty acids. The postprandial increase in plasma CCK concentration was lower on the MCT meal compared with all meals and was greater following the linoleate compared with the low-fat meal. Plasma bile acid concentrations increased 2-3-fold postprandially but the increase was lower following the MCT meal compared with the other meals and was greater on the linoleate meal compared with the low-fat meal. The postprandial increases in plasma chenodeoxycholic acid concentration showed a trend to rise with increasing unsaturation of the test meal. In conclusion, meals rich in linoleate are a potent stimulus for CCK release and lead to prolonged elevations of plasma bile acids and meals containing MCT inhibit CCK release and the subsequent increase in plasma bile acid concentrations.     

Effect of dietary egg on variability of plasma cholesterol levels and lipoprotein cholesterol

The effects of dietary cholesterol on plasma cholesterol levels, its distribution among lipoproteins, and apoproteins of high-density lipoprotein subclasses in individuals who did and did not demonstrate response in plasma cholesterol levels were studied in 21 healthy middle-aged men for 3 mo. After consumption of 3 eggs/day in addition to their habitual diets for 28 days, 21 subjects were divided into 8 hyper- and 13 hypo-responders. The average plasma cholesterol level of the 21 subjects was changed from 188 +/- 36 to 199 +/- 36 mg/100 ml over the 28-day classification period. During the same period the mean plasma cholesterol level of the hyper-responders was significantly increased (p less than 0.025) from 170 +/- 41 to 199 +/- 29 mg/100 ml while that of the hypo-responders fell slightly. The addition of six eggs to the daily diet of the hypo-responders did not alter the mean plasma cholesterol level but resulted in a wide difference in response of plasma cholesterol concentration. The 13 hypo-responders were divided into hypo-hyper-responders (n = 6) and hypo-hypo-responders (n = 7) depending upon the degree of change in plasma cholesterol level. The present study illustrated the variabilities of plasma cholesterol level among free-living subjects who demonstrated two-stage thresholds of response to dietary intake of cholesterol.     

Different effects of zinc and copper deficiency on composition of plasma high density lipoproteins in rats

Male Sprague-Dawley rats (six per group) were fed an egg white-based diet containing 0 or 5 micrograms/g Cu with 1, 10, 100 or 1000 micrograms/g Zn. After 6 wk of feeding, the rats were killed, and the tissues were processed for trace element, lipid and lipoprotein analysis. Copper deficiency was associated with a higher concentration of plasma free cholesterol, high density lipoprotein (HDL) cholesterol and HDL apolipoproteins. Plasma total cholesterol was not significantly affected. No significant differences were noted in HDL lipid composition. However, HDL apo E and apo A-I concentrations were higher with copper deficiency. Lecithin:cholesterol acyltransferase (LCAT) was not affected in a consistent manner by copper status. Varying the amount of zinc in the diet did not produce significant changes in plasma total cholesterol, plasma free cholesterol, HDL cholesterol, or HDL apolipoprotein concentrations. However, HDL from zinc-deficient rats were enriched in free cholesterol and depleted in triglycerides. Furthermore, the concentration of HDL apo C increased as the level of dietary zinc increased.     

Effect of dietary fat and cholesterol on plasma lipids and lipoprotein fractions in normolipidemic men

In a controlled feeding situation, male subjects were assigned to one of four treatment groups: low fat (31% of total kcal)/low cholesterol (193 mg/d) (LFLC), low fat/usual cholesterol (504 mg/d) (LFUC), usual fat (46% of total kcal)/low cholesterol (UFLC) and usual fat/usual cholesterol (UFUC) intake. For the first 2 wk of the 10-wk study all subjects consumed the UFUC diet. Subjects consumed experimental diets during wk 3-7 and resumed their customary intake during wk 8-10. Plasma total, high-density-lipoprotein (HDL), low-density-lipoprotein and very-low-density-lipoprotein cholesterol and triglycerides were determined weekly. A significant effect (P less than 0.05) of dietary fat on plasma total and HDL cholesterol was observed between the end of wk 2 and 7. Low fat intake resulted in 17 +/- 2 mg/dL lower total cholesterol and 10 +/- 1 mg/dL lower HDL cholesterol than the usual fat intake. Plasma lipids were not affected either by dietary cholesterol or by any interaction of dietary fat with cholesterol.     

Effects of dietary fatty acid composition on macronutrient selection and synaptosomal fatty acid composition in rats

Our previous work showed that rats consuming 20% (wt/wt) lard diets selected more protein and less carbohydrate than did rats fed 20% (wt/wt) soybean oil diets. To determine if this effect is specific to saturated fat source and to measure changes in fatty acid composition of synaptosomal phospholipids, male Wistar rats were fed a 20% (wt/wt) soybean oil or tallow diet with 24% protein and 48% carbohydrate for 2 wk. Rats then self-selected from two diets with the same fat previously fed but different protein and carbohydrate composition (5% protein, 67% carbohydrate and 55% protein, 17% carbohydrate). Tallow-fed rats selected more protein and less carbohydrate than did soybean oil-fed rats. Dietary fat also affected fatty acid composition of synaptosomal phospholipids, phosphatidylcholine being most affected and phosphatidylinositol most resistant. Later studies determined if selection differences were due to taste. When rats self-selected without prior exposure to diets, tallow-fed rats selected more protein and less carbohydrate than did soybean oil-fed rats during the last 2 wk but not the first 2 wk. When rats selected from diets with identical protein and carbohydrate composition but different dietary fat, rats consumed slightly greater amounts of the tallow diet at each protein level. The relative intake of tallow and soybean oil diets, however, did not vary significantly with dietary protein treatment. These results confirm that rats fed saturated fat diets select more protein and less carbohydrate than do rats fed polyunsaturated fat diets and suggest this difference is not due to taste factors.