Effects of stearic acid on plasma lipid and lipoproteins in humans

More than 40 years ago, saturated FA with 12, 14, and 16 carbon atoms (lauric acid, myristic acid, and palmitic acid) were demonstrated to be “hypercholesterolemic saturated FA.” It was further concluded that the serum total cholesterol level would hardly be changed by isocaloric replacement of stearic acid (18∶0) by oleic acid (cis-18∶1n−9) or carbohydrates. These earlier studies did not address the effects of the various FA on the serum lipoprotein profile. Later studies found that the hypercholesterolemic saturated FA increase serum total cholesterol levels by raising concentrations of both the atherogenic LDL and the antiatherogenic HDL. Consequently, the ratio of total to HDL cholesterol will hardly change when carbohydrates replace these saturated FA. Compared with other saturated FA, stearic acid lowers LDL cholesterol. Studies on the effects on HDL cholesterol are less conclusive. In some, the effects on HDL cholesterol were comparable to those of palmitic acid, oleic acid, and linoleic acid, whereas in others a decrease was observed. This may suggest that in this respect the source of stearic acid is of importance, which needs however further study. From all these studies, however, it can be concluded that stearic acid may decrease the ratio of total to HDL cholesterol slightly when compared with palmitic or myristic acid. Without doubt, the effects of stearic acid are more favorable than those of trans monounsaturated FA.     

The composition of saturated fatty acids in plasma phospholipids changes in a way to counteract changes in the mean melting point during pregnancy

It has been demonstrated that in pathological conditions with an increase in the calculated mean melting point (MMP) of phospholipid (PL) fatty acids (FA) there are changes in the composition of the saturated FA (SFA), which partially counteract this effect: shorter-chain SFA with lower melting points are increased, while longer-chain less fluid SFA are suppressed. The aim of this study was to determine whether there are differences in MMP during pregnancy and in the newborn and, if so, whether similar adaptive changes occur in the composition of the SFA The FA composition of plasma PL was determined in healthy women (n-16) twice during pregnancy (15–24 wk and 29–36 wk) and at delivery and in umbilical venous blood obtained at birth. The MMP of maternal PL was significantly higher at delivery compared to mid-gestation, due to a loss of highly unsaturated FA (HUFA) which were replaced by SFA. In addition, changes in the SFA occurred; 16∶0 with lower melting point was higher while 18∶0 with higher melting point was lower at delivery. MMP of PL FA in umbilical plasma was lower than in maternal plasma at delivery, which was due to higher HUFA content. In contrast to maternal plasma, 16∶0 was lower while 18∶0, 20∶0 and 24∶0 were higher in umbilical plasma resulting in a higher MMP of SFA, tending to raise the overall MMP. It can be concluded that, during pregnancy and in the newborn, the FA composition of SFA changes in a way to counteract changes in MMP induced by reduced and increased HUFA, respectively.     

Comparison of the effect of the amount and degree of unsaturation of dietary fat on plasma low density lipoproteins in vervet monkeys

The effects of the degree of unsaturation and of the amount of dietary fat on low density lipoprotein (LDL) concentration and composition were determined in vervet monkeys. Diets with fat contents of 41, 31 and 18% energy, each with a low and a high polyunsaturated to saturated fatty acid ratio (P/S; 0.27–0.38 and 1.13–1.47) were fed to six female vervet monkeys for two months. Another six females were given a low fat, high P/S diet for the same period of time, to serve as a reference. The cholesterol contents of the diets were low (21–33 mg per day) and relatively constant. LDL cholesterol concentrations decreased significantly (P≤0.01) when the dietary fat content decreased from 31 to 18% of energy. The dietary P/S ratio only affected LDL cholesterol concentrations during moderate (31% of energy) fat intake, where LDL cholesterol increased (P≤0.01) with a decrease in dietary P/S. Substantial individual variations were observed in LDL cholesterol concentration responses to dietary fat changes. The changes in LDL cholesterol concentrations were the result of changes in the concentration of LDL particles, as the molecular composition did not differ significantly between dietary periods. The high density lipoprotein choelsterol and the plasma triacylglycerol concentrations were not influenced by the dietary fat changes. During the high P/S diets, the percentage of 18∶2 (linoleic acid) increased (P≤0.01) and that of 18∶1 (oleic acid) decreased (P≤0.01) in LDL esterified cholesterol, as compared to the low P/S diets. In adipose tissue triacylglycerol the percentage of 18∶2 was three times higher (P≤0.01) during the high P/S diets than during the low P/S diets. A decrease in the amount of dietary fat (from 31 to 18% of energy) was associated with an increase in the percentage of 18∶1 in LDL esterified cholesterol.     

Hyperphagia modifies FA profiles of plasma phospholipids,plasma FFA,and adipose tissue TAG

Hyperphagia was achieved by continuous intracerebroventricular infusion of a melanocortin receptor antagonist (HS024; Neosystem, Strasbourg, France) in rats. The effects of hyperphagia on FA composition and concentration of plasma phospholipids (PL), plasma FFA, and adipose tissue TAG were studied in rats for 8 d [short-term hyperphagia (STH); n=8], or 28 d [longterm hyperphagia (LTH); n=9]. The control rats were treated with artificial cerebrospinal fluid for 8 d (n=8) or 28 d (n=10). The rats were fed the same regular diet. In STH rats the plasma PL and fasting plasma FFA contained higher concentrations of saturated FA (SFA) and monounsaturated FA (MUFA), and plasma FFA contained lower n−6 PUFA than in the control rats. In LTH rats the plasma PL contained higher concentrations of SFA, MUFA, and n−3 PUFA and higher proportions of 16∶1n−7 and 18∶1n−9 at the expense of 18∶2n−6 than in the control rats. In LTH rats the abundant dietary intake of 18∶2n−6 did not enrich 18∶2n−6 of the plasma PL or adipose tissue TAG. In LTH rats the fasting plasma FFA contained more than twofold higher concentrations of SFA and MUFA, and higher proportions of 16∶1n−7 and 18∶1n−9 at the expense of 18∶2n−6 than in the control rats. This animal obesity model shows that LTH affects the FA composition and concentration of plasma PL, plasma FFA, and adipose tissue TAG, a result consistent with changes associated with increased risk of various diseases in humans. These results also demonstrate that LTH alters the FA composition of plasma PL and adipose tissue TAG in a way that does not reflect the FA composition of dietary fat.     

Species variation in the atherogenic profile of monkeys: Relationship between dietary fats,lipoproteins, and platelet aggregation

Because lipoproteins and platelet aggregation have been implicated in atherogenesis, relative differences in the response of these variables to dietary fat saturation were compared in three species of monkeys differing in their susceptibility to atherosclerosis (cebus, rhesus, and squirrel monkeys). Both long-term (8–12 years) and short-term (8 weeks) responses to diets containing 31% fat calories were examined in the same monkeys. As expected, long-term feeding of coconut oil by comparison to corn oil produced significantly higher plasma concentrations of total cholesterol, LDL cholesterol, apoB, and triglycerides, as well as higher ratios of LDL/HDL cholesterol and apo B/apo A-I. These responses were characteristic of all species with cebus being most responsive and rhesus the least. The shortterm plasma cholesterol response to animal fats (butter, lard, beef tallow) was significantly less than that to coconut oil. When fish oil was substituted for two-thirds of either corn oil or coconut oil, exceptional decreases occurred in plasma cholesterol and triglycerides, as well as in HDL cholesterol and apo A-I concentrations despite the fact that the fish oil diets contained more saturated fat and less polyenes than the corn oil diet. Platelet aggregation tended to increase with saturated fat consumption and greatly decreased with fish oil intake in all monkeys, although cebus monkeys were ten-fold more resistant to platelet aggregation than the other two species. The molecular species of platelet phosphatidylcholine (PC) varied with both the dietary fat fed and species of monkey. An inverse correlation (r=−0.60; p<0.001) was found between changes in one such PC molecular species (18∶0−20∶4) induced by diet and the platelet aggregation threshold. These results demonstrate that the lipemic and platelet responses to dietary saturated fat depend upon both the type of fat (i.e., the specific combination of dietary fatty acids, including the chain length of saturated fatty acids and the degree of polyunsaturation) and the species of monkey (genetic component) in which the response is elicited.     

The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing from a typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)-and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18∶2ω6) and eicosapentaenoic acid (20∶5ω3) and to increases in palmitoleic (16∶1), eicosatrienoic (20∶3ω6) and arachidonic acids (20∶4ω6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16∶1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18∶1 and significant decreases in all ω3 PUFA except 22∶6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18∶2 and 20∶4ω6 and significant decreases in 18∶1, 20∶5ω3 and 22∶5ω3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deteterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the fatty acid profile of the plasma lipids.     

Effects of dietary phenolic compounds on tocopherol, cholesterol, and fatty acids in rats

The effects of the phenolic compounds butylated hydroxytoluene (BHT), sesamin (S), curcumin (CU), and ferulic acid (FA) on plasma, liver, and lung concentrations of α- and γ-tocopherols (T), on plasma and liver cholesterol, and on the fatty acid composition of liver lipids were studied in male Sprague-Dawley rats. Test compounds were given to rats ad libitum for 4 wk at 4 g/kg diet, in a diet low but adequate in vitamin E (36 mg/kg of γ-T and 25 mg/kg of α-T) and containing 2 g/kg of cholesterol. BHT significantly reduced feed intake (P<0.05) and body weight and increased feed conversion ratio; S and BHT caused a significant enlargement of the liver (P<0.001), whereas CU and FA did not affect any of these parameters. The amount of liver lipids was significantly lowered by BHT (P<0.01) while the other substances reduced liver lipid concentrations but not significantly. Regarding effects on tocopherol levels, (i) feeding of BHT resulted in a significant elevation (P<0.001) of α-T in plasma, liver, and lung, while γ-T values remained unchanged; (ii) rats provided with the S diet had substantially higher γ-T levels (P<0.001) in plasma, liver, and lung, whereas α-T levels were not affected; (iii) administration of CU raised the concentration of α-T in the lung (P<0.01) but did not affect the plasma or liver values of any of the tocopherols; and (iv) FA had no effect on the levels of either homolog in the plasma, liver, or lung. The level of an unknown substance in the liver was significantly reduced by dietary BHT (P<0.001). BHT was the only compound that tended to increase total cholesterol (TC) in plasma, due to an elevation of cholesterol in the very low density lipoprotein + low density lipoprotein (VLDL+LDL) fraction. S and FA tended to lower plasma total and VLDL+LDL cholesterol concentrations, but the effect for CU was statistically significant (P<0.05). FA increased plasma high density lipoprotein cholesterol while the other compounds reduced it numerially, but not significantly. BHT, CU, and S reduced cholesterol levels in the liver TC (P<0.001) and percentages of TC in liver lipids (P<0.05). With regard to the fatty acid composition of liver lipids, S increased the n-6/n-3 and the 18∶3/20∶5 polyunsaturated fatty acids (PUFA) ratios, and BHT lowered total monounsaturated fatty acids and increased total PUFA (n−6+n−3). The effects of CU and FA on fatty acids were not highly significant. These results suggest some in vivo interactions between these phenolic compounds and tocopherols that may increase the bioavailability of vitamin E and decrease cholesterol in rats.     

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 (B_max) 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.     

Fatty acid profiles and relative mobilization during fasting in adipose tissue depots of the American marten (Martes americana)

The American marten (Martes americana) is a boreal forest marten with low body adiposity but high metabolic rate. The study describes the FA composition in white adipose tissue depots of the species and the influence of food deprivation on them. American marten (n=8) were fasted for 2 d with 7 control animals. Fasting resulted in a 13.4% weight loss, while the relative fat mass was >25% lower in the fasted animals. The FA composition of the fat depots of the trunk was quite similar to other previously studied mustelids with 14∶0, 16∶0, 18∶0, 16∶1n−7, 18∶1n−9, and 18∶2n−6 as the most abundant FA. In the extremities, there were higher proportions of monounsaturated FA (MUFA) and PUFA. Food deprivation decreased the proportions of 16∶0 and 16∶1n−7, while the proportion of long-chain MUFA increased in the trunk. The mobilization of FA was selective, as 16∶1n−7, 18∶1n−9, and particular n−3 PUFA were preferentially mobilized. Relative mobilization correlated negatively with the carbon chain length in saturated FA (SFA) and n−9 MUFA. The Δ9 desaturation of SFA enhanced the mobilization of the corresponding MUFA, but the positional isomerism of the first double bond did not correlate consistently with relative mobilization in MUFA or PUFA. In the marten, the FA composition of the extremities was highly resistant to fasting, and the tail tip and the paws contained more long-chain PUFA to prevent the solidification of lipids and to maintain cell membrane fluidity during cooling.     

Incorporation of n−3 fatty acids into plasma and liver lipids of rats: Importance of background dietary fat

The health benefits of long-chain n−3 PUFA (20∶5n−3 and 22∶6n−3) depend on the extent of incorporation of these FA into plasma and tissue lipids. This study aimed to investigate the effect of the background dietary fat (saturated, monounsaturated, or n−6 polyunsaturated) on the quantitative incorporation of dietary 18∶3n−3 and its elongated and desaturated products into the plasma and the liver lipids of rats. Female weanling Wistar rats (n=54) were randomly assigned to six diet groups (n=9). The fat added to the semipurified diets was tallow (SFA), tallow plus linseed oil (SFA-LNA), sunola oil (MUFA), sunola oil plus linseed oil (MUFA-LNA), sunflower oil (PUFA), or sunflower oil plus linseed oil (PUFA-LNA). At the completion of the 4-wk feeding period, quantitative FA analysis of the liver and plasma was undertaken by GC. The inclusion of linseed oil in the rat diets increased the level of 18∶3n−3, 20∶5n−3, and, to a smaller degree, 22∶6n−3 in plasma and liver lipids regardless of the background dietary fat. The extent of incorporation of 18∶3n−3, 20∶5n−3, and 22∶5n−3 followed the order SFA-LNA>MUFA-LNA>PUFA-LNA. Levels of 22∶6n−3 were increased to a similar extent regardless of the type of major fat in the rat diets. This indicates that the background diet affects the incorporation in liver and plasma FA pools of the n−3 PUFA with the exception of 22∶6n−3 and therefore the background diet has the potential to influence the already established health benefits of long-chain n−3 fatty acids.     

Effect of modified dairy fat on postprandial and fasting plasma lipids and lipoproteins in healthy young men

Fatty acid profile of milk fat can be modified by cow feeding strategies. Our aim was postprandially and after 4 wk to compare the effect of a modified milk fat (M diet) [with 16% of the cholesterolemic saturated fatty acid (C12–16) replaced by mainly oleic and stearic acids] with the effect of D diet, including a conventional Danish milk fat on plasma lipids and lipoproteins. A side effect of the cow feeding regime was a 5% (w/w) increase in trans fatty acid in M diet. Eighteen subjects were fed for two periods of 4 wk strictly controlled isoenergetic test diets with 40% of energy from total fat and the same content of dietary cholesterol in a randomized study with cross-over design. Contrary to expectations, fasting low density lipoprotein (LDL) cholesterol concentration did not differ after the experimental periods. However, M diet resulted in a higher fasting total triacylglycerol concentration compared to D diet (P=0.009). Postprandial samples were taken at two different occasions (i) at day 21, after breakfast and lunch and (ii) on the last day of the study 2, 4, 6, and 8 h after a fat load. Postprandial plasma triacylglycerol and chylomicron triacylglycerol showed higher peak values after D diet than M diet (interaction effect, diet × times P<0.05). In conclusion, M diet did not lower LDL cholesterol compared to D diet. Thus any cholesterol-lowering effect of oleic and stearic acids may have been obscured by the high content of cholesterol-raising saturated fatty acids in milk fat. A higher content of the trans fatty acids in M diet might have counteracted the cholesterol neutral/decreasing effect and increased plasma triacylglycerol.     

Fasting and postprandial lipid response to the consumption of modified milk fats by guinea pigs

The objective of the present study was to investigate the effect of three modified milk fats with different melting profiles on fasting and postprandial lipid responses and on fecal fat content in guinea pigs. We hypothesized that the consumption of modified milk fat with a high m.p. results in reduced fasting and postprandial lipid responses compared with that of modified milk fat fractions with lower m.p. To test this hypothesis, male Hartley guinea pigs were fed isoenergetic diets containing 110 g of fat/kg, either from one of the three modified milk fats with high (HMF), medium (MMF), or low melting profiles (LMF), or from one of the two reference fats as whole mil fat (MF) or a fat blend similar to that of nonhydrogenated soft margarine (MA) for 28 d. Food intake (P<0.05) and body weight gain (P<0.05) were reduced in the animals fed the HMF diet compared with the other groups. In the fasting state, plasma LDL cholesterol was highest in animals fed the LMF diet, intermediary in those fed the MMF and MF diets, and lowest in those fed the HMF and MA diets (P<0.05). Postprandially, the areas under the 0- to 3-h curves for the changes in plasma TG were lower in the HMF group than in the MA- and LMF-fed guinea pigs (P<0.05). The fecal fat content was higher (P<0.05) in the HMF group compared to the other milk fat groups. The present results suggest that modified milk fats can impact food intake, body weight gain, fasting cholesterolemia, and postprandial triglyceridemia, and these changes may be attributed to an altered fat absorption.     

Postprandial Lipid Responses do not Differ Following Consumption of Butter or Vegetable Oil when Consumed with Omega-3 Polyunsaturated Fatty Acids

Dietary saturated fat (SFA) intake has been associated with elevated blood lipid levels and increased risk for the development of chronic diseases. However, some animal studies have demonstrated that dietary SFA may not raise blood lipid levels when the diet is sufficient in omega‐3 polyunsaturated fatty acids (n‐3PUFA). Therefore, in a randomised cross‐over design, we investigated the postprandial effects of feeding meals rich in either SFA (butter) or vegetable oil rich in omega‐6 polyunsaturated fatty acids (n‐6PUFA), in conjunction with n‐3PUFA, on blood lipid profiles [total cholesterol, low density lipoprotein cholesterol (LDL‐C), high density lipoprotein cholesterol (HDL‐C) and triacylglycerol (TAG)] and n‐3PUFA incorporation into plasma lipids over a 6‐h period. The incremental area under the curve for plasma cholesterol, LDL‐C, HDL‐C, TAG and n‐3PUFA levels over 6 h was similar in the n‐6PUFA compared to SFA group. The postprandial lipemic response to saturated fat is comparable to that of n‐6PUFA when consumed with n‐3PUFA; however, sex‐differences in response to dietary fat type are worthy of further attention.     

Betaine supplementation affects the cholesterol but not the lipid profile of pigs

This study was undertaken to investigate the effects of long term betaine intake on the cholesterol and lipid profile of Alentejano (AL) pigs. At ?36 kg body weight (BW), castrated male and female pigs fed a commercial (C) diet, were divided into two groups: i) Group C, consuming the C diet; and ii) Group CB, consuming the C diet supplemented with 1 g/kg betaine. Pigs were slaughtered at ?100 kg BW. Fasting plasma concentrations of protein, urea, glucose, TAG, phospholipids, homocysteine, total and LDL‐ and HDL‐cholesterol were determined. Liver TAG, phospholipids, and total and free cholesterol were analyzed, as well as total lipids, cholesterol contents, and fatty acid (FA) composition of M. semimembranosus and dorsal subcutaneous fat. Betaine supplemented pigs presented significantly higher plasma concentrations of TAG, phospholipids, cholesterol, and lipoprotein cholesterol. Dorsal subcutaneous fat cholesterol concentration was also significantly higher in CB than in C pigs. No differences were detected in the most abundant FA profile (including the unsaturated to saturated FA ratio) of muscle and subcutaneous fat tissues among treatments. These data suggest that betaine induces dyslipidemia, and increases cholesterol concentration in dorsal subcutaneous fat, without affecting the FA profile of M. semimembranosus and dorsal subcutaneous fat.     

Low-fat diets do not lower plasma cholesterol levels in healthy men compared to high-fat diets with similar fatty acid composition at constant caloric intake

In most studies reporting the effects of high-fat (HF) and low-fat (LF) diets on human plasma fatty acids (FA) and lipoprotein levels, the design involved adding to the diet an oil that had an FA composition (FAC) very different from the FAC of the control diet. Thus, it is difficult to determine if simply reducing the fat content of the diet without changing the dietary FAC changes the tissue FAC or alters plasma lipid levels. In this study, we fed diets that contained either 22 or 39% of calories from fat, but had no differences in their FAC, for 50 d to a group (n=11) of healthy men (20–35 y). Thus, the polyunsaturated/saturated ratios (1.0) of the diets were identical as were the n−3/n−6 ratio and the monounsaturated-to-total fat ratios. The diets contained (wt% of total fat) approximately 28% saturated FA, 33% monounsaturatedcis-FA, 6% monounsaturatedtrans-FA, 22% n−6 polyunsaturated FA, and 7% n−3 polyunsaturated FA, and 4% other minor FA. The diets consisted of natural foods and were formulated to contain 16 en% protein, either 45 or 62 en% carbohydrate (CHO) and at least the recommended dailyallowance for all micronutrients. Both diets contained 360 mg of cholesterol per day. All subjects were given the HF diet for 20 d, and then six were placed on the LF and the other five remained on the HF diet for 50 d. The two groups were crossedover for the remaining 50 d of the study. The subjects' baseline total cholesterol level was 173 mg/dl, after 50 d on the HF diet it was 177 mg/dl and after 50 d on the LF diet, 173 mg/dl. The differences were not significant, and there were no significant changes in either the LDL or HDL cholesterol levels with either diet. Triglyceride levels, and consequently very low density lipoprotein levels, rose significantly on the LF, higher CHO diet compared to the levels found in the subjects on the HF diet (91.5 and 66.4 mg/dl respectively,P<0.002). The linoleic acid content of the plasma, platelets, and red blood cells was significantly (P<0.05) reduced in the LF diet compared to HF diet, without any obvious physiological effects. Hence, many earlier observations indicating reductions in plasma lipid levels when people are on LF diets may be due to changes in the FAC of the diet, not the reduction in fat calories.     

Effect of apolipoprotein E polymorphism on serum lipoprotein response to saturated fatty acids

This report summarizes two studies which investigated the effects of apolipoprotein E (apoE) polymorphism on the serum total cholesterol (TC) and lipoprotein cholesterol responses to 8∶0+10∶0 and 12∶0 diets (Study I) and 14∶0, 16∶0, and 18∶0 diets (Study II). Eighteen healthy premenopausal women (3 apoE 3/2, 12 apoE 3/3, 3 apoE 4/3) in study I and another 18 healthy premenopausal women (4 apoE 3/2, 10 apoE 3/3, 3 apoE 4/3, 1 apoE 4/2) in study II consumed a baseline diet providing 40 en% total fat, 11 en % 18∶2, 15 en% 18∶1, 11.5 en% saturated fat for the first week of each 5-wk period. The experimental diets for both studies provided 40 3n% total fat, 13–14 en% as one of five test saturated fatty acids (SFA), 14–16 en% 18∶1, and 3–4 en% 18∶2. Analysis by apoE phenotypes showed that both the 8∶0+10∶0 diet and the 12∶0 diet in Study Linduced significant increases in serum TC in subjects with different apoE phenotypes with the exception of apoE 3/2 in the medium-chain triglyceride group. In contrast, in Study II, individuals with apoE 4/3 consuming the 14∶0 diet showed significant increases in serum TC, high density lipoprotein-cholesterol (HDL-C), and HDL2-C, but the same subjects consuming the 16∶0 diet showed significant increases in serum TC and low density lipoprotein-cholesterol. The findings from both studies indicated serum lipoprotein responses to SFA were different and the variation of responsiveness may be regulated, at least in part, by apoE polymorphism, especially when 14∶0, 16∶0, or 18∶0 was consumed.     

Response of plasma lipids to dietary cholesterol and wine polyphenols in rats fed polyunsaturated fat diets

This experiment was designed to evaluate the effects of dietary red wine phenolic compounds (WP) and cholesterol on lipid oxidation and transport in rats. For 5 wk, weanling rats were fed polyunsaturated fat diets (n−6/n−3=6.4) supplemented or not supplemented with either 3 g/kg diet of cholesterol, 5 g/kg diet of WP, or both. The concentrations of triacylglycerols (TAG, P<0.01) and cholesterol (P<0.0002) were reduced in fasting plasma of rats fed cholesterol despite the cholesterol enrichment of very low density lipoprotein + low density lipoprotein (VLDL+LDL). The response was due to the much lower plasma concentration of high density lipoprotein (HDL) (−35%, P<0.0001). In contrast, TAG and cholesteryl ester (CE) accumulated in liver (+120 and +450%, respectively, P<0.0001). However, the cholesterol content of liver microsomes was not affected. Dietary cholesterol altered the distribution of fatty acids mainly by reducing the ratio of arachidonic acid to linoleic acid (P<0.0001) in plasma VLDL+LDL (−35%) and HDL (−42%) and in liver TAG (−42%), CE (−78%), and phospholipids (−28%). Dietary WP had little or no effect on these variables. On the other hand, dietary cholesterol lowered the α-tocopherol concentration in VLDL+LDL (−40%, P<0.003) and in microsomes (−60%, P<0.0001). In contrast, dietary WP increased the concentration in microsomes (+21%, P<0.0001), but had no effect on the concentration in VLDL+LDL. Cholesterol feeding decreased (P<0.006) whereas WP feeding increased (P<0.0001) the resistance of VLDL+LDL to copper-induced oxidation. The production of conjugated dienes after 25 h of oxidation ranged between 650 (WP without cholesterol) and 2,560 (cholesterol without WP) μmol/g VLDL+LDL protein. These findings show that dietary WP were absorbed at sufficient levels to contribute to the protection of polyunsaturated fatty acids in plasma and membranes. They could also reduce the consumption of α-tocopherol and endogenous antioxidants. The responses suggest that, in humans, these substances may be beneficial by reducing the deleterious effects of a dietary overload of cholesterol.     

The effect of fatty acid composition of rapeseed oil on plasma lipids and oxidative stability of low‐density lipoproteins in cholesterol‐fed hamsters

We studied the effect of four rapeseed oils with different fatty acid profiles on parameters implicated in the pathogenesis of atherosclerosis in humans in a model experiment with hamsters. The hamsters were divided into seven groups and fed a semi‐synthetic, cholesterol‐enriched diet (5 g/kg diet) containing 15% of the fat in question for a period of six weeks. The following rapeseed oils were used: (1) conventional rapeseed oil (6% saturated fatty acids [SFA], 64% monounsaturated fatty acids [MUFA], 18% linoleic acid [LA], 9% α‐linolenic acid [ALA]), (2) linoleic acid‐rich rapeseed oil (6% SFA, 61% MUFA, 28% LA, 2% ALA), (3) oleic acid‐rich rapeseed oil (6% SFA, 74% MUFA, 11% LA, 5% ALA), (4) myristic acid‐rich rapeseed oil (11% myristic acid, 35% SFA, 44% MUFA, 14% LA, 5% ALA). Sunflower oil, olive oil and lard were used as control fats. The concentrations of the lipids in the plasma, in the lipoprotein fractions and in the liver, the fatty acid composition of various tissues, the tocopherol status and the susceptibility of low‐density lipoproteins (LDL) to in vitro‐oxidation were determined. The concentrations of total cholesterol found in the plasma and in the LDL fraction and the ratios of LDL to HDL were similar after feeding the four different types of rapeseed oil, sunflower oil and olive oil. Lard produced the highest concentrations of cholesterol in plasma and the LDL fraction and the highest ratio of LDL to HDL. Feeding conventional, oleic acid‐ and myristic acid‐rich rapeseed oils resulted in markedly lower ratios of arachidonic to eicosapentaenoic acid in the lipids of the liver and the erythrocytes. This is considered beneficial for the formation of eicosanoids. The lag‐time before the onset of peroxidation of the LDL lipids, induced by copper ions, was not statistically significant between the seven hamster groups suggesting that the susceptibility of LDL to lipid peroxidation was similar after feeding all types of fat. Considering all parameters obtained in the used hamster model it is obvious that all four rapeseed oils are at least as favourable as olive oil or sunflower oil.     

Variations of <Emphasis Type="Italic">trans</Emphasis> octadecenoic acid in milk fat induced by feeding different starch-based diets to cows

The impact of starch sources differing in their velocities of ruminal degradation on the milk fat of dairy cows was studied. The animals received diets containing a slowly degradable (potatoes) or rapidly degradable (wheat) starch concentrate (40% of the dry matter) in a total mixed diet. Milk fat was the only animal performance factor affected: Cows produced significantly less milk fat when fed the wheat diet than the potato diet (−3.3 g/kg, −122 g/d; P<0.05). With the wheat diet, milk fat was poorer in short-chain FA and richer in unsaturated longchain FA, especially in trans octadecenoic acid (4.4 vs. 2.7% of the total FA, P<0.05). A very large increase in the isomer trans-10 18∶1 (+1.46% of the total FA) was observed. Because no difference in volatile FA concentrations in the rumen was revealed, the increase in trans octadecenoic acids, and particularly the isomer trans-10 18∶1, was associated with the larger postprandial drop in ruminal pH with wheat. Similar concentrate levels and FA profiles in both diets indicated that the decrease in milk fat was due to changes in the ruminal environment. Quicker degradation of wheat starch, and hence a greater drop in pH with this diet associated with the absence of any effect on volatile FA, strengthen the hypothesis developed in the literature of enzyme inhibition via increased levels of trans octadecenoic acids, especially the trans-10 isomer. Hence, milk fat can be decreased with rapidly degradable starch sources and not only with high levels of concentrates in the diet or added fat. More detailed work is necessary to elucidate the microorganisms involved and to determine whether metabolic pathways similar to those reported for high-concentrate diets are involved.     

Triglyceride composition of bovine milk fat with elevated levels of linoleic acid

The effect of increasing the linoleic acid (18∶2) content of milk fat on the composition and structure of the triglycerides (TG) was investigated. Protected sunflower seed supplement was added to the diet of a cow grazing on pasture, and the structure and composition of the milk fat compared with the milk fat from its monozygous twin which had been fed a control diet. The relative proportions of TG fractions of high, medium, and low molecular weight in the milk fat with elevated levels of 18∶2 (15.5% 18∶2) were 43.0, 19.5, and 37.5 moles %, respectively, compared with 36.1, 19.7, and 44.2 moles %, respectively, in the milk fat from the cow fed the control diet. Separation of these three TG fractions of each milk fat into TG classes with different levels of unsaturation showed that the milk fat with elevated levels of 18∶2 contained higher proportions of diene, triene, and tetraene TG and correspondingly lower proportions of saturated and, to a lesser extent, monoene TG. The saturated and monoene TG from the two milk fats had similar fatty acid compositions. However, the diene TG of the 18∶2-rich milk fat included high proportions of the combination of 18∶2 with two saturated fatty acids (FA) which are minor constituents of normal milk fats. Likewise, the triene TG reflected the presence of 18∶2 in combination with 18∶1 and a saturated FA.