Dietary fatty acids, lipoproteins, and cardiovascular disease

Plasma lipoproteins in preruminant calves fed diets containing tallow or soybean oil with and without cholesterol

Five-week-old, preruminant male calves were fed milk replacer containing tallow or soybean oil (230 g/ kg of dietary DM) with and without cholesterol (10 g/ kg of dietary DM) for 17 d in order to study changes in plasma lipids and lipoproteins. Dietary soybean oil induced higher cholesterolemia than did tallow because of a specific increase in plasma concentrations of large high density lipoproteins of type 1 (1.026 to 1.060 g/ml), but plasma concentrations of low and very low density lipoproteins were not modified. Addition of cholesterol to diets containing either tallow or soybean oil markedly increased plasma concentrations of intermediate and low density lipoproteins, suggesting partial inhibition of the low density lipoprotein receptor activity in tissue. By contrast, dietary cholesterol added to the diet containing soybean oil led to an increase in plasma concentrations of type 1 high density lipoproteins and of light high density (1.060 to 1.091 g/ml) lipoproteins. These data indicated that the soybean oil diet, which was rich in linoleic acid, did not reduce the effects of dietary cholesterol on the metabolism of low and high density lipoproteins in the preruminant calf.

Effects of dietary fatty acid composition on plasma cholesterol

It should be clear from the preceding sections that the effects of dietary fatty acids on plasma lipids get more complicated the more we try to simplify them! We have presented one argument as to how different fatty acids may interact to impact human plasma lipids. This is by no means an endorsement that ours is the only argument. Nevertheless, a strong case can be made for 14:0 and 18:2 as being the key players in this scenario. The role of palmitic acid seems to be the most controversial. While clearly certain studies do indeed reveal 16:0 to be hypercholesterolemic relative to 18:1, the data from studies suggesting that it behaves similarly to 18:1 are equally compelling. What is certain is that it is erroneous to assume that 16:0 is the major cholesterol-raising SFA simply because it is the most abundant SFA in the diet. Clearly, 18:0 cannot be considered cholesterol-elevating. One is therefore left with the 12-16C SFA. However, 12:0 and 14:0 are only of concern if diets contain palm-kernel, coconut oil or dairy products as major dietary constituents. Accordingly one is left with 16:0 and its response is highly dependent on the metabolic status as well as the age of the subjects being used. While "elderly" hypercholesterolemic humans clearly benefit from decreased 16:0 (and all SFA) consumption, "younger" normocholesterolemic subjects fail to show such clear-cut effects. Additionally, the concomitant levels of dietary cholesterol and 18:2 also have a major bearing on the cholesterolemic response of 16:0 As far as guidelines for the general public are concerned, clearly for people with TC > 225 and LDL-C > 130 mg/dl and/or those who are overweight (i.e. those percieved to be at high risk), the primary emphasis should clearly be on reducing total fat consumption. Decreasing saturated fat consumption will invariably also lower dietary cholesterol consumption. The latter manouver will generally lower TC and LDL-C. Whether the reduction occurs because of the removal of 14:0, or 16:0 and/or dietary cholesterol is a mute point, since most dietary guidelines advocate curtailing intake of animal and dairy products, which will result in reductions of all the SFA. It remains to be established whether life-long adherence to the above dietary guidelines in those subjects with normal cholesterol levels and an absence of the other conventional risk factors for CHD, will result in a subsequent decrease in CHD risk. In the latest NCEP report 39 million Americans were targeted as those who would benefit from reductions in LDL-C, principally by dietary means. This is indeed a very high number. But that leaves almost 220 million Americans! For them the age old recommendation to consume a moderate fat load, maintain ideal body weight and eat a varied and balanced diet would still appear to be the most powerful advice.

The role of stereospecific saturated fatty acid positions on lipid nutrition

The saturated fatty acids in the sn-1 and -3 position of triacylglycerols can exhibit different metabolic patterns due to their low absorptivity. This means that dietary fats containing saturated fats primarily in sn-1 and -3 positions (e.g., cocoa butter, coconut oil, and palm oil) can have very different biological consequences than those fats in which the saturated fats are primarily in the sn-2 position (e.g., milk fat and lard). Differences in stereospecific fatty acid location should therefore be an important consideration in the design and interpretation of lipid nutrition studies and in the production of specialty food products.

Low density lipoprotein binding to monolayer cultures of hepatocytes isolated from hamsters fed different dietary fatty acids

(i) The aim of these studies was to investigate the effect of dietary cholesterol and dietary fat on the expression of the hepatic low density lipoprotein (LDL) receptor. (ii) Low density lipoprotein (LDL) binding to monolayer cultures of hepatocytes isolated from hamsters fed different amounts of cholesterol and fats was measured. (iii) Hepatocytes isolated from hamsters fed a low cholesterol diet (< 0.008% w/w) specifically bound LDL and this binding increased with time in culture. By comparison, LDL binding to hepatocytes isolated from hamsters fed 0.12% (w/w) cholesterol was lower and there was no time dependent increase. Intermediate levels of binding were seen for hepatocytes from hamsters fed 0.06% (w/w) cholesterol. (iv) In hamsters fed 10% (w/w) fat in the presence of 0.06% (w/w) cholesterol, significantly more LDL receptors were expressed by hepatocytes from animals fed safflower oil compared to those isolated from lard or olive oil fed animals. (v) The reduced LDL cholesterol concentrations frequently observed for hamsters fed polyunsaturated fatty acids thus reflects an increase in the number of LDL receptors expressed in the liver. However, other explanations are needed for the effects of monounsaturated fatty acids.

Carbohydrate-fat exchange and regulation of hepatic cholesterol and plasma lipoprotein metabolism in the guinea pig

Adult female guinea pigs were fed semipurified diets containing increasing concentrations of saturated fat (2.5%, 7.5%, 15%, and 25% wt/wt) to determine effects of exchanging fat-carbohydrate calories on lipoprotein metabolism. Plasma very-low-density lipoprotein (VLDL) and high-density lipoprotein (HDL) did not vary but plasma low-density lipoprotein (LDL) concentrations increased with increasing fat calories. LDL cholesterol values were 42 +/- 25, 61 +/- 17, 92 +/- 25, and 98 +/- 21 mg/dL (mean +/- SD, n = 5), respectively. The relative proportion of cholesteryl ester increased and triacylglycerol (TAG) decreased for VLDL, LDL, and HDL as dietary fat increased. Plasma lecithin cholesterol acyltransferase (LCAT) activity was positively correlated with HDL cholesteryl ester content. Hepatic cholesterol and TAG concentrations were highest in animals fed 25% fat (P < .01). Hepatic apolipoprotein (apo) B/E receptor maximal binding capacity (Bmax) was 30% higher in animals fed 2.5% and 7.5% fat as compared with those fed 15% and 25% fat (P < .01) and inversely correlated with plasma LDL (r = -.85, P < .01). In contrast, HDL binding to guinea pig hepatic membranes exhibited a significant positive correlation with dietary fat quantity (r = .98, P < .001), consistent with a dose-response with increasing fat calories. The activity of hepatic 3-hydroxy-3-methyl glutaryl coenzyme A (HMG CoA) reductase was not affected by the amount of dietary fat, whereas the activity of acyl CoA:cholesterol acyltransferase (ACAT) was significantly increased in animals fed 25% fat (P < .05). Hepatic free-cholesterol and ACAT activity exhibited a positive correlation for all dietary groups (r = .75, P < .001). These results demonstrate that exchange of saturated dietary fat for carbohydrate calories results in significant modifications in the regulation of metabolic pathways that determine plasma LDL concentrations and hepatic cholesterol homeostasis.

Carbohydrate type and amount alter intravascular processing and catabolism of plasma lipoproteins in guinea pigs

To test the effects of exchanging dietary complex and simple carbohydrate for fat calories on lipoprotein metabolism, guinea pigs were fed two different fat/carbohydrate ratios: 2.5:58% (w/w) or 25:29% (w/w) with either sucrose or starch as the carbohydrate source. Animals fed high-fat had higher plasma low-density lipoprotein (LDL) and hepatic cholesterol concentrations than animals fed low-fat diets (P < 0.01). The cholesteryl ester content per particle was higher, and the number of triacylglycerol (TAG) molecules was lower in very low density lipoprotein (VLDL) and LDL from animals fed high-fat diets. Intake of high-fat/sucrose resulted in higher plasma LDL concentrations than intake of high-fat/starch, and animals fed low-fat/starch had the highest plasma TAG concentrations associated with VLDL particles containing more TAG molecules, as well as a TAG-enriched LDL. The activity of plasma lecithin cholesteryl:acyl transferase (LCAT) was highest in animals fed high-fat/sucrose, and heart lipoprotein lipase (LPL) activity was higher in animals fed high-fat diets. Hepatic apoprotein B/E (apo B/E) receptor number (Bmax) was increased 21% with low-fat diets (P < 0.01). These results suggest that the hypercholesterolemia induced by high-fat and by sucrose intake are associated with a higher plasma LCAT activity which results in a cholesteryl ester-enriched VLDL which, by the action of LPL, might be more readily converted to LDL through the delipidation cascade leading to downregulation of hepatic apo B/E receptors. The hypertriglyceridemia associated with low-fat intake may result from increased production of VLDL TAG, which would explain the increased TAG content and the higher TAG/CE ratio of VLDL from animals fed the low-fat/starch diet.

Alteration of plasma lipids in the rat by fractionation of modified milk fat (butterfat)

Our objective was to determine the nutritional effects of defined fat fractions of modified milk fat, or butterfat (anhydrous butter without the milk fat globule membrane) on lipid and lipoprotein cholesterol concentrations in plasma of rats fed diets containing 16% fat and two amounts of cholesterol. Five dietary fats were compared: 1) intact butterfat, 2) a liquid butterfat fraction enriched in oleic acid and unsaturated triacylglycerols with < 40 carbon atoms, 3) a solid butterfat fraction enriched in palmitic and stearic acids, 4) corn oil, and 5) palm oil. The extent of diet-induced hypercholesterolemia was the greatest with palm oil, followed by solid butterfat, corn oil, intact butterfat, and the lowest with liquid butterfat. Triacylglycerol concentrations in plasma were greater for rats fed palm oil than for those fed corn oil or liquid or intact butterfat. Among the high cholesterol dietary groups, ingestion of the liquid butterfat diet resulted in similar lipoprotein cholesterol and very low density lipoprotein concentrations relative to the corn oil diet, and ingestion of the solid butterfat diet resulted in similar lipoprotein cholesterol and very low density lipoprotein concentrations relative to the palm oil diet. These results suggest that changes in the triacylglycerol and fatty acid composition of butterfat by fractionation processes may improve its nutritional profile.

[Effect of rapeseed in beef cattle feeding on fatty acid composition, vitamin E content and oxidative stability of body fat]

Four groups of five fattening bulls each consumed a concentrate--wheat straw-diet (2.5:1) supplemented with either 0, 7, 14 or 21% ground rape seed for 350 days. Rape seed contained 427 g crude fat (ether extract) and 127 mg vitamin E per kg dry matter. The supplementation with rapeseed increased the fat concentrations in the rations from 25 to 50, 75 and 100 g, and of vitamin E from 11 to 19, 26 and 34 mg per kg dry matter. All bulls were slaughtered with about 560 kg body weight. Fatty acid composition of depot fat and of the fat of musc. long. dorsi were determined by gas liquid chromatography. Vitamin E concentrations in blood, depot fat and muscle were determined by HPLC. Oxidative stability of depot fat was measured as induction time by means of rancimat-test. Rape seed supplementation decreased C16-fatty acids and increased C18-fatty acids in depot and muscle fat. Muscle fat contained significantly more mono and poly unsaturated fatty acids (40.2 and 7.4%) than depot fat (33.5 and 2.0%, respectively). Rape seed supplementation enhanced significantly the vitamin E-concentrations in all body samples. In depot fat vit. E increased from 4.5 to 7.3, 8.5 and 14.9 micrograms/g. Induction time increased from 10.9 to 18.5, 16.1 and 19.5 h, when 0, 7, 14 or 21% rapeseed were added.

The effects of different dietary fats and cholesterol on serum lipoprotein concentrations in hamsters

(i) We have studied the effect of dietary cholesterol and fat on lipoprotein concentrations in the male Golden Syrian hamster. (ii) On a low fat diet, dietary cholesterol increased the cholesterol concentration in all the major serum lipoprotein fractions. It also increased the storage of cholesterol ester in the liver. (iii) In the absence of added dietary cholesterol, additional dietary fat had little influence on serum or hepatic cholesterol concentrations, and this is irrespective of the nature of the dietary fat. (iv) In the presence of 0.12% (w/w) cholesterol, lard (rich in saturated fatty acids) increased serum VLDL cholesterol and triacylglycerol concentrations. By contrast, olive oil (rich in oleic acid) had no effect on VLDL lipid concentrations and sunflower oil, rich linoleic acid, reduced them. (v) Lard also increased serum LDL cholesterol concentrations in cholesterol-fed animals. Olive oil reduced LDL cholesterol concentrations and sunflower oil had no effect. (vi) In cholesterol-fed animals, lard had no effect on the hepatic cholesterol ester concentration, while both olive and sunflower oil increased it. This increase was significantly higher in olive oil-fed hamsters compared to those fed sunflower oil. (vii) Thus, in this species, the primary effects of dietary fat on lipoprotein metabolism appear to represent a modulation of the effects of dietary cholesterol. In cholesterol-fed hamsters we confirm the hypercholesterolaemic effects of saturated fatty acids and highlight important differences in the effects of mono- and poly-unsaturated fatty acids on lipoprotein metabolism.

Dietary fat saturation modifies the metabolism of LDL subfractions in guinea pigs

The effects of dietary fat saturation on the metabolism of low-density lipoprotein (LDL) subfractions were measured in adult male guinea pigs fed semipurified diets containing 15% (wt/wt) corn oil (CO; 58% linoleic acid), lard (24% palmitic/14% stearic acid), or palm kernel oil (PK; 52% lauric/18% myristic acid). Animals fed the CO diet had lower plasma total cholesterol levels than guinea pigs fed the PK or lard diets (P < .01). Plasma LDL-1 (d = 1.019 to 1.05 g/mL) concentrations were 3.5- and 2.4-fold higher in animals fed the PK diet compared with the CO and lard groups, respectively, while LDL-2 (d = 1.05 to 1.09 g/mL) concentrations were not different among groups. For all dietary fat groups LDL-1 had a higher molecular weight and a larger diameter than LDL-2. LDL fractional catabolic rates (FCRs) varied, depending on both the diet and the LDL subfraction. Animals fed the polyunsaturated CO diet had a more rapid LDL FCR than animals from the other two groups (P < .01). Within the same diet group, LDL-2 exhibited a slower turnover rate than LDL-1 in animals fed the PK diet, while no differences in LDL subfraction FCR were found in the CO and lard groups. Animals fed the PK and lard diets did not exhibit significant modifications in the density distribution of LDL subfractions over a period of 33 hours. In contrast, animals fed the CO diet exhibited a shift of more buoyant to denser LDL particles, suggesting that differences in LDL intravascular processing are mediated by dietary fat saturation. In vitro LDL binding to hepatic membranes confirmed the in vivo data with an increased expression of apolipoprotein B/E receptors (Bmax) in animals fed the CO diet (P < .01). Hepatic apolipoprotein B/E receptors exhibited less affinity for LDL-2 in the PK group, a result consistent with the less rapid turnover of LDL-2 in PK-fed animals. The results suggest that dietary fatty acids varying in saturation and composition have distinctive atherogenic potentials. The lowest plasma LDL cholesterol concentrations mediated by CO intake could in part be explained by induced changes in the composition and processing of LDL subfractions, resulting in faster LDL turnover rates in addition to increased expression of hepatic apolipoprotein B/E receptors.(ABSTRACT TRUNCATED AT 400 WORDS)