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

Dietary alpha-linolenic acid, EPA, and DHA have differential effects on LDL fatty acid composition but similar effects on serum lipid profiles in normolipidemic humans

Our aim was to study the effects of increased dietary intake of alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) on serum lipids and LDL fatty acid compositions. To this end, a controlled parallel study was conducted in 74 healthy normolipidemic men and women aged 19-43 y. Participants were randomly assigned to 1 of 3 interventions and consumed a total intake of 4.4 g/d ALA (ALA group), 2.2 g/d EPA (EPA group), and 2.3 g/d DHA (DHA group) for 6 wk. Fatty acid ethyl esters were incorporated into margarines, which replaced the participant's normal spread. The ALA, EPA, or DHA intake led to a significant enrichment of the LDL with the respective (n-3) fatty acid. In addition, LDL EPA contents in the ALA group increased by 36% (P < 0.05) with no changes in LDL DHA. The EPA intervention led to an additional enrichment with DHA (24%; P < 0.001), whereas the DHA intervention further increased the amount of EPA (249%; P < 0.001). ALA, EPA, or DHA intake did not affect fasting serum concentrations of total and LDL cholesterol, but fasting serum triacylglycerol concentrations significantly decreased in the EPA (-0.14 mmol/L) and DHA (-0.30 mmol/L) interventions and also in the ALA intervention (-0.17 mmol/L). DHA intake significantly increased serum HDL cholesterol, whereas no changes were found with ALA or EPA intake. In conclusion, the present data support the hypothesis that isolated dietary ALA, EPA, and DHA intakes lead to differential enrichment in LDL due to interconversion. Moderate amounts of ALA, EPA, and DHA are effective in improving lipid profiles of normolipidemic humans.

Small Dense Low-Density Lipoprotein Concentration and Oxidative Susceptibility Changes after Consumption of Soybean Oil, Rice Bran Oil, Palm Oil and Mixed Rice Bran/Palm Oil in Hypercholesterolaemic Women

The effects of a diet containing soybean oil (SBO), rice bran oil (RBO), palm oil (PO) or a RBO/PO (3:1) mixture on the composition and oxidation of small dense low-density lipoproteins (sdLDL) in 16 hypercholesterolaemic women were investigated. During the 8-week control period, participants consumed a free-choice weight-maintaining diet comprising carbohydrate (55% energy), protein (15% energy) and fat (30% energy) with < 300 mg/day of cholesterol. During each 10-week study period, participants consumed this same diet but with the addition of one of the three test oils or the RBO/PO mixture. Total cholesterol and low-density lipoprotein (LDL)-cholesterol levels were significantly reduced during SBO, RBO and RBO/PO consumption, while high-density lipoprotein cholesterol was significantly decreased by SBO consumption. There was a significant reduction in sdLDL-cholesterol levels only after using SBO and it tended to be reduced during RBO/PO consumption, whereas it was significantly increased following PO consumption. The sdLDL oxidation lag time was significantly increased during PO, RBO/PO and RBO consumption, but significantly reduced following SBO. The results for the RBO/PO mixture suggest that this oil mixture might further reduce the risk of atherosclerosis.

Modified egg composition to reduce low-density lipoprotein oxidizability: high monounsaturated fatty acids and antioxidants versus regular high n-6 polyunsaturated fatty acids

Eggs high in n-6 PUFA, predominant in Western markets, were found to increase blood LDL oxidation, suggesting a new health concern beyond raising cholesterol. Protective composition was explored by increasing egg antioxidants and MUFA and reducing n-6 PUFA. Lag times to plasma LDL oxidation were significantly shortened with two eggs/day of high-PUFA compositions compared to a low-egg (2-4/week) regime, by 28.8% following "HPUFA-regular" ( p < 0.01) and by 27.2% following antioxidant-fortified "HPUFA-HAOX" ( p < 0.01). However, two "HMUFA-HAOX" eggs/day with reduced egg n-6 PUFA FA% (LA by 30.7%) and PUFA:MUFA ratio (LA:OA by 45.8%) plus increased antioxidants (vitamin E 500%, carotenoids 260%), resulting in increased plasma OA 33.3%, vitamin E 22.4%, and carotenoids 55.0% ( p < 0.01), were associated with lag-time only 6.6% shorter than low-egg (NS). Among health-oriented egg modifications, here for the first time they reduced associated LDL oxidization, consistent with anti-inflammation and antioxidant paradigms, warranting further research on functional advantages of antioxidative egg composition.

Changes in the phenolic content of low density lipoprotein after olive oil consumption in men. A randomized crossover controlled trial

Olive oil decreases the risk of CVD. This effect may be due to the fatty acid profile of the oil, but it may also be due to its antioxidant content which differs depending on the type of olive oil. In this study, the concentrations of oleic acid and antioxidants (phenolic compounds and vitamin E) in plasma and LDL were compared after consumption of three similar olive oils, but with differences in their phenolic content. Thirty healthy volunteers participated in a placebo-controlled, double-blind, crossover, randomized supplementation trial. Virgin, common, and refined olive oils were administered during three periods of 3 weeks separated by a 2-week washout period. Participants were requested to ingest a daily dose of 25 ml raw olive oil, distributed over the three meals of the day, during intervention periods. All three olive oils caused an increase in plasma and LDL oleic acid (P < 0·05) content. Olive oils rich in phenolic compounds led to an increase in phenolic compounds in LDL (P < 0·005). The concentration of phenolic compounds in LDL was directly correlated with the phenolic concentration in the olive oils. The increase in the phenolic content of LDL could account for the increase of the resistance of LDL to oxidation, and the decrease of thein vivooxidized LDL, observed in the frame of this trial. Our results support the hypothesis that a daily intake of virgin olive oil promotes protective LDL changes ahead of its oxidation.

Dietary modeling shows that the substitution of canola oil for fats commonly used in the United States would increase compliance with dietary recommendations for fatty acids

OBJECTIVE

To examine the effect of substituting canola oil for selected vegetable oils and canola oil-based margarine for other spreads on energy, fatty acid, and cholesterol intakes among US adults.

DESIGN

Twenty-four-hour food recall data from the 1999-2002 National Health and Nutrition Examination Survey (NHANES) were used to calculate the effect of substituting canola oil for dietary corn, cottonseed, safflower, soybean, and vegetable oils described as "not further specified" and of canola oil-based margarine for other spreads at 25%, 50%, and 100% replacement levels.

SUBJECTS

Adult participants aged>or=20 years (n=8,983) of the 1999-2002 NHANES.

STATISTICAL ANALYSIS

Sample-weighted mean daily intake values and the percentage of subjects meeting dietary recommendations were estimated at the various replacement levels. Standard errors of the means and percentages were estimated by the linearization method of SUDAAN.

RESULTS

Significant (P<0.05) changes compared to estimated actual intakes included: saturated fatty acid intake decreased by 4.7% and 9.4% with 50% and 100% substitution, respectively. Complete substitution increased monounsaturated fatty acid and alpha-linolenic acid intakes by 27.6% and 73.0%, respectively, and decreased n-6 polyunsaturated fatty acid and linoleic acid intakes by 32.4% and 44.9%, respectively. The ratio of n-6 to n-3 fatty acids decreased from 9.8:1 to 3.1:1 with 100% replacement. Energy, total fat, and cholesterol intakes did not change.

CONCLUSIONS

Substitution of canola oil and canola oil-based margarine for most other vegetable oils and spreads increases compliance with dietary recommendations for saturated fatty acid, monounsaturated fatty acid, and alpha-linolenic acid, but not for linoleic acid, among US adults.

Olive oil containing olive oil fatty acid esters of plant sterols and dietary diacylglycerol reduces low-density lipoprotein cholesterol and decreases the tendency for peroxidation in hypercholesterolaemic subjects

Plant sterols (PS) and MUFA are well-documented cholesterol lowering agents. We aimed to determine the effect of PS esterified to olive oil fatty acids (PS-OO) on blood lipid profile and lipid peroxidation in hypercholesterolaemic subjects. Twenty-one moderately overweight, hypercholesterolaemic subjects consumed three consecutive treatment diets, each lasting 28 d and separated by 4-week washout periods, using a randomized crossover design. Diets contained 30 % energy as fat, 70 % of which was provided by olive oil (OO), and differed only in the treatment oils: OO, PS esterified to sunflower oil fatty acids (PS-SO), and PS-OO. Both PS-SO and PS-OO treatments provided 1·7 g PS /d. PS-OO and PS-SO consumption resulted in a decrease (P = 0·0483) in LDL-cholesterol (LDL-C) concentrations compared with the OO diet. Although total cholesterol and apo B-100 levels were not significantly affected, PS-SO and, to some extent, PS-OO reduced the total:HDL-cholesterol (HDL-C) ratio (P = 0·0142) and the apo B-100:apo A-I ratio (P = 0·0168) compared with the OO diet. There were no differences across diets in lipoprotein(a) (Lp(a)) and lipid peroxidation levels. However, following consumption of OO and PS-SO, Lp(a) concentrations increased (P = 0·0050 and 0·0421, respectively), while PS-OO treatment did not affect Lp(a) levels. Furthermore, there was a decrease (P = 0·0097) in lipid peroxidation levels with PS-OO treatment during the supplementation phase. Our results suggest that supplementing an OO-rich diet with PS-OO favourably alters the plasma lipid profile and may decrease the susceptibility of LDL-C to lipid peroxidation in hypercholesterolaemic subjects.

Influence of three rapeseed oil-rich diets, fortified with alpha-linolenic acid, eicosapentaenoic acid or docosahexaenoic acid on the composition and oxidizability of low-density lipoproteins: results of a controlled study in healthy volunteers

OBJECTIVE

To compare the individual effects of dietary alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) on low-density lipoprotein (LDL) fatty acid composition, ex vivo LDL oxidizability and tocopherol requirement.

DESIGN, SETTING AND SUBJECTS

A randomized strictly controlled dietary study with three dietary groups and a parallel design, consisting of two consecutive periods. Sixty-one healthy young volunteers, students at a nearby college, were included. Forty-eight subjects (13 males, 35 females) completed the study.

INTERVENTIONS

Subjects received a 2-week wash-in diet rich in monounsaturated fatty acids (21% energy) followed by experimental diets enriched with about 1% of energy of ALA, EPA or DHA for 3 weeks. The omega-3 (n-3) fatty acids were provided with special rapeseed oils and margarines. The wash-in diet and the experimental diets were identical, apart from the n-3 fatty acid composition and the tocopherol content, which was adjusted to the content of dienoic acid equivalents.

RESULTS

Ex vivo oxidative susceptibility of LDL was highest after the DHA diet, indicated by a decrease in lag time (-16%, P<0.001) and an increase in the maximum amount of conjugated dienes (+7%, P<0.001). The EPA diet decreased the lag time (-16%, P<0.001) and the propagation rate (-12%, P<0.01). Tocopherol concentrations in LDL decreased in the ALA group (-13.5%, P<0.05) and DHA group (-7.3%, P<0.05). Plasma contents of tocopherol equivalents significantly decreased in all three experimental groups (ALA group: -5.0%, EPA group: -5.7%, DHA group: -12.8%). The content of the three n-3 polyunsaturated fatty acid differently increased in the LDL: on the ALA diet, the ALA content increased by 89% (P<0.001), on the EPA diet the EPA content increased by 809% (P<0.001) and on the DHA diet, the DHA content increased by 200% (P<0.001). In addition, the EPA content also enhanced (without dietary intake) in the ALA group (+35%, P<0.01) and in the DHA group (+284%, P<0.001).

CONCLUSIONS

Dietary intake of ALA, EPA or DHA led to a significant enrichment of the respective fatty acid in the LDL particles, with dietary EPA preferentially incorporated. In the context of a monounsaturated fatty acid-rich diet, ALA enrichment did not enhance LDL oxidizability, whereas the effects of EPA and DHA on ex vivo LDL oxidation were inconsistent, possibly in part due to further changes in LDL fatty acid composition.

Dietary polyunsaturated fat intake is associated with low-density lipoprotein size, but not with susceptibility to oxidation in subjects with impaired glucose metabolism and type II diabetes: the Hoorn study

OBJECTIVE

A high monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) intake is associated with lower plasma low-density lipoprotein (LDL)-cholesterol. However, PUFA may increase the susceptibility of LDL to undergo oxidative modifications. The aim of this study was to analyze the association of habitual dietary fat intake with LDL size and oxidizability.

DESIGN

Cross-sectional.

SETTING

Cohort study.

SUBJECTS

Seven hundred and fifty-eight subjects with normal, impaired glucose metabolism and type II diabetes.

INTERVENTIONS

Mean LDL size was measured by high-performance gel-filtration chromatography. In vitro oxidizability of LDL was determined by measuring lag time, reflecting the resistance of LDL to copper-induced oxidation. Information about dietary fat intake was obtained by a validated food frequency questionnaire.

RESULTS

PUFA intake (energy percent) was significantly and negatively associated with LDL size in subjects with type II diabetes (standardized beta (95% confidence interval) -0.17 (-0.28;-0.06)) and impaired glucose metabolism - although not statistically significant - (-0.09 (-0.24;0.05)), but not in subjects with normal glucose metabolism (0.01 (-0.10;0.12)) (P-value for interaction=0.02). No significant associations were observed for total, saturated fat and MUFA intake with LDL size. Intake of fat was associated with lag time; however, the small magnitude of the associations suggested that the composition of dietary fat is not a major factor affecting lag time. The same association with lag time was observed in all three glucose metabolism categories.

CONCLUSIONS

In individuals with abnormal glucose metabolism, higher PUFA intake is associated with smaller LDL particle size, but does not alter the susceptibility of LDL to in vitro oxidation.

SPONSORSHIP

Dutch Diabetes Research Foundation, and the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO).

Associations between hypertriglyceridemia, dietary fat intake, oxidative stress, and endothelial activation in men

OBJECTIVE

We examined the associations between intake of different types of dietary fat and plasma levels of oxidative stress and endothelial activation markers in men.

METHODS

For that purpose, a complete physical and metabolic profile was assessed. Dietary habits of subjects were determined with a 3-d food record. We also measured fasting plasma 8-iso-prostaglandin F2alpha and oxidized low-density lipoprotein concentrations and soluble forms of vascular cell adhesion molecule-1 (sVCAM-1), intercellular adhesion molecule-1 (sICAM-1), and E-selectin. All these measurements were performed with commercial enzyme-linked immunosorbent assay kits and standards.

RESULTS

We found that a high total dietary fat intake was associated with high plasma sICAM-1 (r = 0.40, P < 0.005), sVCAM-1 (r = 0.31, P < 0.05), and E-selectin (r = 0.28, P < 0.05) levels. We also found that in men matched for plasma triacylglycerol levels, those consuming a diet rich in total fat (>105 g/d, n = 21) were characterized by higher circulating levels of sICAM-1 (P < 0.05) and E-selectin (P < 0.05) compared with triacylglycerol-matched individuals with a low total dietary fat intake (<105 g/d, n = 21). However, no significant difference was noted in plasma oxidized low-density lipoprotein levels between groups. Further, we conducted multivariate analyses and found that saturated fatty acid intake was the only dietary variable after inclusion of other dietary variables that contributed to circulating sICAM-1 (P < 0.05) and sVCAM-1 (P < 0.05).

CONCLUSION

Our study suggests that high dietary fat consumption is associated with endothelial activation in men and that this detrimental effect is likely attributable to the saturated fatty acid content of the diet.

Effect of dietary n−6 and n−3 polyunsaturated fatty acids on peroxidizability of lipoproteins in steers

The susceptibility of major plasma lipoproteins to lipoperoxidation was studied in relation to the FA composition of their neutral and polar lipids in steers given PUFA-rich diets. Two trials used, respectively, 18 ("sunflower" experiment, S) or 24 ("linseed" experiment, L) crossbred Salers x Charolais steers. Each involved three dietary treatments over a 70-d period: a control diet (CS or CL diets) consisting of hay and concentrate, or the same diet supplemented with oilseeds (4% diet dry matter) fed either as seeds (SS or LS diets) or continuously infused into the duodenum (ISO or ILO diets). Compared with control diets, ISO and ILO treatments tended to decrease the resistance time of LDL and HDL classes to peroxidation, mainly owing to the enrichment of their polar and neutral lipids with PUFA. With diets SS and LS, sensitivity of major lipoprotein classes (LDL, light and heavy HDL) was not affected because ruminal hydrogenation of dietary PUFA decreased their incorporation into lipoparticles. ISO and ILO treatments induced a more important production of conjugated dienes and hydroperoxides generated by peroxidation in the three lipoprotein classes due to the higher amounts of PUFA esterified in lipids of the core and the hydrophilic envelope of particles. The production of malondialdehyde (MDA) increased in steers fed linseed supplements, indicating that MDA production did not occur with linoleic acid provided by sunflower oil supplements. Thus, plasma peroxidation of PUFA generates toxic products in steers fed diets supplemented with PUFA and can be deleterious for the health of the animal during long-term treatment.

Mediterranean diet has no effect on markers of inflammation and metabolic risk factors in patients with coronary artery disease

OBJECTIVE

Mediterranean diet is associated with decreased levels of inflammatory markers and metabolic risk factors in epidemiologic studies and recent trials on patients with metabolic syndrome. Given the recent improvements in medical treatments, it is unclear if such beneficial effects are also present in patients with coronary artery disease (CAD). We therefore investigated the effect of Mediterranean diet on markers of inflammation and metabolic risk factors in patients with treated CAD.

DESIGN

Randomized, controlled trial.

SUBJECTS

A total of 101 patients (59.4+/-8.6 years, 23% female) with established and treated CAD (80% statins).

INTERVENTIONS

Participants were assigned to a Mediterranean diet group (MG; n=48) with a 1-year program of 100 h of education, or to a written advice-only group (AG; n=53). Before and after intervention, we measured serum high-sensitivity C-reactive protein (hs-CRP), fibrinogen, fasting insulin, homocysteine, serum lipids and plasma fatty acids.

RESULTS

The Mediterranean diet program increased the intakes of fish, fruits/vegetables and moderately of canola/olive oil and increased plasma concentrations of long-chain n-3 polyunsaturated fatty acids in the MG. Median hs-CRP and mean fibrinogen, homocysteine, fasting insulin, triglycerides and serum cholesterols remained unchanged in both groups.

CONCLUSIONS

Adoption of a Mediterranean diet by patients with medically treated CAD has no effect on markers of inflammation and metabolic risk factors.

SPONSORSHIP

Alfried Krupp Foundation, Essen, Germany.

Effects of dietary n-6 or n-3 polyunsaturated fatty acids protected or not against ruminal hydrogenation on plasma lipids and their susceptibility to peroxidation in fattening steers1

Two experiments were conducted using crossbred Salers x Charolais fattening steers fed diets enriched with no supplemental oilseeds or oils rich in either n-6 PUFA (from sunflower seeds) or n-3 PUFA (from linseeds) provided either as seeds incorporated in the diet (i.e., not protected from ruminal bacterial hydrogenation) or by chronic infusion into the duodenum (protected form). In the Sunflower experiment, animals (initial age = 454 +/- 20 d; initial BW = 528 +/- 36 kg) received a control diet for 70 d (CS, n = six) consisting of hay and concentrate, or the same basal diet supplemented with sunflower oil (4% of dietary DM), either fed as seeds (SS, n = six) or infused into the duodenum (ISO, n = six). The same experimental design was applied to animals (initial age = 412 +/- 33 d; initial BW = 536 +/- 33 kg) used in the Linseed experiment (CL, LS, and ILO; n = 8 per group). For all animals, blood was sampled every 15 d during 70 d. In both trials, a significant diet x time interaction (P < 0.001) was detected for plasma concentrations of apolipoprotein A-I, phospholipids, and free and esterified cholesterol, with values increasing with time during administration of the PUFA-rich diets being more evident with ISO and ILO diets. Plasma fatty acids were altered with oil infusions, with increased concentrations of n-6 (1.6-fold; P < 0.05) and n-3 PUFA (4.5-fold; P < 0.05) and of their respective indicies of peroxidizability (1.2- and 1.5-fold with Diets ISO and ILO, respectively; P < 0.05). In vitro copper-induced peroxidation of lipids revealed a decreased length of the lag phase in the process of conjugated diene generation by 48% (P < 0.005) with the ILO diet, indicating less resistance against peroxidation than in control steers. Compared with CS, the ISO treatment increased plasma alpha-tocopherol (x2.5; P < 0.05) leading to similar resistance against peroxidation. After depletion of this vitamin, the rates of peroxidation and production of conjugated dienes were greater (twofold; P < 0.05) with the ISO and ILO diets than with the others. In conclusion, infusion of sunflower or linseed oil into the duodenum altered the composition and distribution of plasma lipids and increased the plasma concentration of PUFA. The sensitivity of plasma PUFA to peroxidation depends on the plasma level of antioxidants, especially vitamin E, a nutrient important both for the health of animals and for the stability of the blood lipids until their tissue deposit.

Changes in plasma antioxidant capacity and oxidized low-density lipoprotein levels in men after short-term cranberry juice consumption

Low-density lipoprotein (LDL) oxidation is closely implicated in the development of atherosclerotic cardiovascular disease (CVD), and thus, reducing LDL susceptibility to oxidation with antoxidants could be of importance in CVD prevention. Flavonoids, polyphenolic compounds found in a large selection of fruits and vegetables, have been characterized as having a strong antioxidant potential, and intake of flavonoid-rich foods has been related to decreased morbidity and mortality from heart disease. The present study was therefore undertaken to investigate the effect of flavonoid-rich cranberry juice supplementation on plasma lipoprotein levels and LDL oxidation. For that purpose, 21 men (age +/- SD, 38 +/- 8 years) were enrolled in a 14-day intervention and instructed to drink cranberry juice 7 mL/kg body weight per day. Physical and metabolic measures including plasma lipid and oxidized LDL (OxLDL) concentrations as well as antioxidant capacity were performed before and after the intervention. At baseline, we found that plasma OxLDL levels were significantly associated with waist circumference ( r = 0.47, P = .0296) as well as plasma triglyceride ( r = 0.68, P = .0007) and apolipoprotein B ( r = 0.91, P < .0001) concentrations. The intervention led to a reduction in plasma OxLDL levels (-9.9% +/- 17.8%, P = .0131) and increase in antioxidant capacity (+6.5% +/- 10.3%, P = .0140). However, no relationship was found between both of these changes ( r = -.01, not significant). The intervention did not result in any improvement of plasma lipoprotein-lipid or inflammatory marker concentrations. Our results show that short-term cranberry juice supplementation is associated with significant increase in plasma antioxidant capacity and reduction in circulating OxLDL concentrations. Although the physiological relevance of our observations needs to be further examined, our study supports the potential role of antioxidant-rich foods in maintaining health and preventing CVD.

Effect of alpha linolenic acid on cardiovascular risk markers: a systematic review

OBJECTIVE

To determine whether dietary supplementation with alpha linolenic acid (ALA) can modify established and emerging cardiovascular risk markers.

DESIGN

Systematic review and meta-analysis of randomised controlled trials identified by a search of Medline, Embase, Cochrane Controlled Trials Register (CENTRAL), and the metaRegister of Controlled Trials (mRCT).

PATIENTS

All human studies were reviewed.

MAIN OUTCOME MEASURES

Changes in concentrations of total cholesterol, low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, triglyceride, fibrinogen, and fasting plasma glucose, and changes in body mass index, weight, and systolic and diastolic blood pressure.

RESULTS

14 studies with minimum treatment duration of four weeks were reviewed. ALA had a significant effect on three of the 32 outcomes examined in these studies. Concentrations of fibrinogen (0.17 micromol/l, 95% confidence interval (CI) -0.30 to -0.04, p = 0.01) and fasting plasma glucose (0.20 mmol/l, 95% CI -0.30 to -0.10, p < 0.01) were reduced. There was a small but clinically unimportant decrease in HDL (0.01 mmol/l, 95% CI -0.02 to 0.00, p < 0.01). Treatment with ALA did not significantly modify total cholesterol, triglycerides, weight, body mass index, LDL, diastolic blood pressure, systolic blood pressure, VLDL, and apolipoprotein B.

CONCLUSIONS

Although ALA supplementation may cause small decreases in fibrinogen concentrations and fasting plasma glucose, most cardiovascular risk markers do not appear to be affected. Further trials are needed, but dietary supplementation with ALA to reduce cardiovascular disease cannot be recommended.

Omega-6 fatty acids and coronary artery disease: the pros and cons

Polyunsaturated fatty acids have long been recommended as a beneficial substitute for atherogenic saturated fat. The connection between dietary lipids and blood cholesterol is still under debate, as is the connection between dietary fat and coronary artery disease. Thus, the lipid hypothesis is still a hypothesis. The major dietary polyunsaturated fatty acid, linoleic acid of the omega-6 family, has several properties that render it hyperinsulinemic and atherogenic. The potential benefits of linoleic acid intake regarding coronary artery disease, and its possible harms, are discussed.

Fatty acids and atherosclerotic risk

Most research concerning the effects of dietary fatty acids on atherosclerotic risk has focused on their effects on lipid and lipoprotein metabolism. However, it is known that fatty acids also influence a number of other relevant mechanisms involved in atherosclerosis such as lipid peroxidation, inflammation and haemostasis. The most favourable distribution of cholesterol over the various lipoproteins is achieved when saturated and trans fatty acids are replaced by a mixture of cis-unsaturated fatty acids. Furthermore, fatty acids from fish oil lower triacylglycerol concentrations. Effects on other atherosclerotic risk markers are less evident. Monounsaturated fatty acids maybe preferable above other fatty acids with respect to low-density lipoprotein oxidation as measured by indirect in vitro assays. The relevance of these assays for the in vivo situation is, however, limited. With respect to inflammation, mainly the effects of n-3 polyunsaturated fatty acids from fish oil have been studied, but results were inconsistent. Also results from studies evaluating the effects of fatty acids on haemostatic risk markers were inconsistent, which may be partly related to the use of different analytical methods. The most consistent finding however is the potential beneficial effect of moderate intakes of fish oil on platelet aggregation. Furthermore, reducing total fat intake rather than changing the fatty acid composition of the diet may beneficially affect the coagulation system. In conclusion, while beneficial effects on atherosclerotic risk are mainly ascribed to cis-unsaturated fatty acids, it remains debateable whether trans and saturated fatty acids in the diet have to be replaced by cis-unsaturated fatty acids or by carbohydrates. To answer this question adequately more validated methods are needed that reflect in vivo lipid peroxidation, inflammation and haemostasis.

Review of dietary recommendations for diabetes mellitus

Previous nutritional guidelines for people with diabetes focused on carbohydrate-based meal planning. Updated guidelines from Europe and North America reflect a more flexible approach to nutritional intervention. New aspects of these most recent recommendations include: (1) increased emphasis on the role of trained dietitians for educating people with diabetes; (2) greater individualization of dietary choices based on cultural, regional and personal preferences; (3) more flexibility for choosing between carbohydrate and monounsaturated fat consumption, but with limitations on intake of polyunsaturated fats (<10% of total energy); (4) broadened allowance of sucrose in the diet (up to 10% of total energy); and (5) greater recognition of physical activity as an important means to control weight and enhance general health. Expert guidelines vary regarding preferential intake of carbohydrates with lower glycemic indices.

Individual serum triglyceride responses to high-fat and low-fat diets differ in men with modest and severe hypertriglyceridemia

It is not yet clear whether a low-fat or a high-fat diet is more suitable for the treatment of hypertriglyceridemia. Therefore, we conducted a dietary study with nonobese hypertriglyceridemic men using a randomized crossover design. After a 2-wk acclimation period, the subjects were randomly assigned to 2 groups. One group consumed a low-fat (29% of energy) diet for 3 wk, followed first by a 2-wk washout period, then a 3-wk high-fat (40% of energy) diet period. The second group consumed the low- and high-fat diets in reverse order. Both diets were isocaloric, rich in monounsaturated fatty acids (MUFAs) and long-chain (n-3)-PUFAs, and contained no alcohol. Absolute amounts of long-chain (n-3)-PUFAs and fiber were similar, as were the fatty acid and carbohydrate compositions. Serum triglyceride concentrations in fasting subjects decreased during the high-fat diet period by 34% (95% CI = -19 to -46%, P = 0.001), and during the low-fat diet period by 31% (95% CI = -0.5 to -51.8%, P = 0.048). Triglyceride concentrations did not differ between the low- and high-fat diet periods. However, the high-fat diet lowered triglyceride concentrations more effectively in all subjects with a baseline triglyceride concentration < 4.5 mmol/L, whereas the low-fat diet lowered triglyceride levels more effectively in half of the subjects with a baseline value > 4.5 mmol/L. Based on these findings, we recommend a high-fat triglyceride-lowering diet for patients with only slightly elevated serum triglyceride concentrations (<4.5 mmol/L). However, a lower-fat diet is more suitable for some subjects with more distinctly elevated triglyceride concentrations.

Cardiovascular effects of milk enriched with ω-3 polyunsaturated fatty acids, oleic acid, folic acid, and vitamins E and B6 in volunteers with mild hyperlipidemia

OBJECTIVE

Results from epidemiologic studies and clinical trials have indicated that consumption of omega-3 fatty acids, oleic acid, and folic acid have beneficial effects on health, including decreased risk of cardiovascular disease. We evaluated the combined effects of these nutrients through the consumption of milk enriched with omega-3 polyunsaturated fatty acids, oleic acid, vitamins E and B6, and folic acid on risk factors for cardiovascular disease in volunteers with mild hyperlipidemia.

METHODS

Thirty subjects ages 45 to 65 y (51.3 +/- 5.3 y) were given 500 mL/d of semi-skimmed milk for 4 wk and then 500 mL/d of the enriched milk for 8 wk. Plasma and low-density lipoproteins were obtained at the beginning of the study and at 4, 8, and 12 wk.

RESULTS

Consumption of enriched milk for 8 wk increased plasma concentrations of docosahexaenoic acid and eicosapentaenoic acid and significantly (P < 0.05) decreased plasma concentrations of triacylglycerol (24%), total cholesterol (9%), and low-density lipoprotein cholesterol (13%). Plasma and low-density lipoprotein oxidation and vitamin E concentration remained unchanged throughout the study. Significant decreases in plasma concentrations of vascular cell adhesion molecule-1 (9%) and homocysteine (17%) were found, accompanied by a 98% increase in plasma concentration of folic acid.

CONCLUSIONS

Dairy supplementation strategies with omega-3 polyunsaturated fatty acids, oleic acid, and vitamins may be useful for decreasing risk factors for cardiovascular disease.

A solid dietary fat containing fish oil redistributes lipoprotein subclasses without increasing oxidative stress in men

There is a demand and need for healthy solid dietary fats. However, synthetic fats can be tailored to contain specific physiologic properties. Our goal was to design dietary solid test fats that would be both beneficial to the atherogenic lipid profile and stable against lipid peroxidation. Sixteen men (age 35-75 y) substituted 80 g of their normal dietary fat intake with test fat for two periods of 21 d each in a double-blind, randomized, crossover study. Although solid, both test fats were low in cholesterol-raising SFA. Test fat "F" contained 5 g/100 g long chain (n-3) fatty acids matched by oleic acid in test fat "O." Plasma total triacylglycerol (TAG), VLDL TAG, cholesterol in VLDL, and intermediate density lipoproteins (IDL) were lower (P < 0.05), whereas apolipoprotein (apo) B of the large LDL-2 (d = 1031-1042 g/L) subclass, and cholesterol of HDL(2b) subclass, were higher after intake of F than O fat (P < 0.05). There was no difference in the effect on in vivo oxidation measured as the ratio of plasma isoprostanes F(2) to arachidonic acid and urinary isoprostanes, whereas the vitamin E activity/plasma total lipids ratio was higher after intake of F than O (P = 0.008). In conclusion, a solid dietary fat containing (n-3) PUFA decreased plasma TAG, VLDL, and IDL cholesterol, and redistributed lipoprotein subclasses in LDL and HDL, with a higher concentration of the larger and less atherogenic subfractions. These changes took place without an increase in oxidative stress as measured by in vivo markers.

Associations of low density lipoprotein particle composition with atherogenicity

PURPOSE OF REVIEW

A growing body of data suggests that in addition to LDL-cholesterol concentrations, compositional properties of LDL, including size and fatty acid composition, are important in determining the relative degree of atherogenicity. This review examines current research in this field to evaluate which properties of LDL may most directly influence the risk of coronary heart disease.

RECENT FINDINGS

The presence of small dense LDL has been correlated with an increased risk of coronary heart disease, but this has not been shown to be fully independent of related factors such as elevated plasma triacylglycerol concentrations. An increased susceptibility of small dense LDL to in-vitro oxidation has also been demonstrated, but its importance to coronary heart disease risk has not been established. Other studies have found that the presence of enlarged LDL, modified (oleate enriched) fatty acyl composition of LDL, and higher numbers of LDL particles in plasma also are endpoints associated with an increased risk of coronary heart disease.

SUMMARY

LDL size may indicate a metabolic condition associated with increased CHD risk as opposed to the direct promotion of atherosclerosis by specific particle types of LDL. In most claims of detrimental effects of small dense LDL, neither LDL particle concentrations nor the fatty acid composition of the particles were established, both factors being important in contributing to the atherogenic potential of LDL. The predisposition to premature coronary heart disease cannot currently be objectively assigned to any one type of LDL particle.

The implementation of nutritional advice for people with diabetes

These consensus-based recommendations emphasize the practical implementation of nutritional advice for people with diabetes, and describe the provision of services required to provide the information. Important changes from previous recommendations include greater flexibility in the proportions of energy derived from carbohydrate and monounsaturated fat, further liberalization in the consumption of sucrose, more active promotion of foods with a low glycaemic index, and greater emphasis on the provision of nutritional advice in the context of wider lifestyle changes, particularly physical activity. Monounsaturated fats are now promoted as the main source of dietary fat because of their lower susceptibility to lipid peroxidation and consequent lower atherogenic potential. Consumption of sucrose for patients who are not overweight can be increased up to 10% of daily energy provided that this is eaten in the context of a healthy diet and distributed throughout the day [corrected]. Evidence is presented for the effectiveness of advice provided by trained dieticians. The increasing evidence for the importance of good metabolic control and the growing requirement for measures to prevent Type 2 diabetes in an increasingly obese population will require major expansion of dietetic services if the standards in National Service Frameworks are to be successfully implemented.

Dietary lipids in the aetiology of Alzheimer's disease: implications for therapy

Amyloid plaques and neurofibrillary tangles are the neuropathological hallmarks of Alzheimer's disease (AD), but no conclusive evidence has emerged showing that these hallmarks are the cause and not a product of the disease. Many studies have implicated oxidation and inflammation in the AD process, and there is growing evidence that abnormalities of lipid metabolism also play a role. Using epidemiology to elucidate risk factors and histological changes to suggest possible mechanisms, the hypothesis is advanced that dietary lipids are the principal risk factor for the development of late-onset sporadic AD. The degree of saturation of fatty acids and the position of the first double bond in essential fatty acids are the most critical factors determining the effect of dietary fats on the risk of AD, with unsaturated fats and n-3 double bonds conferring protection and an overabundance of saturated fats or n-6 double bonds increasing the risk. The interaction of dietary lipids and apolipoprotein E isoforms may determine the risk and rate of sustained autoperoxidation within cellular membranes and the efficacy of membrane repair. Interventions involving dietary lipids and lipid metabolism show great promise in slowing or possibly averting the development of AD, including dietary changes, cholesterol-modifying agents and antioxidants.

Thermally oxidized dietary fats increase the susceptibility of rat LDL to lipid peroxidation but not their uptake by macrophages

The aim of this study was to investigate the effect of dietary oxidized fats on the lipoprotein profile and the atherogenicity of LDL. Two experiments with male Sprague-Dawley rats were conducted. In Experiment 1, diets with either fresh fat or oxidized fat, prepared by heating at temperatures of 50, 105 or 190 degrees C, containing either 25 or 250 mg alpha-tocopherol equivalents/kg were used. In Experiment 2, diets with fresh or oxidized fat, heated at a temperature of 55 degrees C, containing 25 mg alpha-tocopherol equivalents/kg, were used. In Experiment 1, rats fed all types of oxidized fats had higher concentrations of HDL cholesterol and lower ratios between plasma and HDL cholesterol than rats fed the diet containing the fresh fat. As determined from the lag time, the susceptibility of LDL to copper-induced lipid peroxidation was higher in rats fed oxidized fats heated at 105 or 190 degrees C than in rats fed the diets containing the fresh fat or the oxidized fat treated at 50 degrees C, irrespective of the dietary vitamin E concentration. However, in Experiment 2, the composition of LDL apolipoproteins and uptake of LDL by macrophages were not different between rats fed the fresh fat diet and those fed the oxidized fat diet. We conclude that ingestion of oxidized fats does not adversely affect the lipoprotein profile in the rat model used, and does not cause modifications of apolipoproteins that would lead to enhanced uptake of LDL via macrophage scavenger receptors.

Dietary mono- and polyunsaturated fatty acids similarly increase plasma apolipoprotein A-IV concentrations in healthy men and women

We investigated the effect of dietary fatty acid composition on plasma apolipoprotein (apo) A-IV concentrations. Plasma apo A-IV concentrations were measured by ELISA in plasma of 48 healthy men and women in a controlled dietary study. First, all participants consumed a 2-wk baseline diet rich in saturated fatty acids (SFA). Then, they were randomly assigned to one of three dietary treatments, which contained refined olive oil [rich in monounsaturated fatty acids (MUFA), n = 17], rapeseed oil [rich in MUFA and alpha-linolenic acid [18:3(n-3)], n = 13], or sunflower oil [rich in (n-6) PUFA, n = 18] as the principal source of fat for 4 wk. The plasma concentrations of apo A-IV increased when subjects consumed the diets rich in unsaturated fatty acids, by 16% or 13.0 mg/L [F((2,76)) = 12.874, P < 0.001 by repeated-measures ANOVA]. The increase was not affected by diet group affiliation, gender or apo A-IV genotype. In conclusion, diets rich in unsaturated fatty acids, independent of the degree of unsaturation, gender and apo A-IV genotype, increase plasma apo A-IV concentrations compared with a baseline diet rich in SFA in healthy men and women.

The degree of unsaturation of dietary fatty acids and the development of atherosclerosis (review)

Atherosclerosis is the principal contributor to the pathogenesis of myocardial and cerebral infarction, gangrene and loss of function in the extremities. It results from an excessive inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. Atherosclerotic lesions develop fundamentally in three stages: dysfunction of the vascular endothelium, fatty streak formation and fibrous cap formation. Each stage is regulated by the action of vasoactive molecules, growth factors and cytokines. This multifactorial etiology can be modulated through the diet. The degree of unsaturation of dietary fatty acids affects lipoprotein composition as well as the expression of adhesion molecules and other pro-inflammatory factors, and the thrombogenicity associated with atherosclerosis development. Thus, the preventive effects of a monounsaturated-fatty acid-rich diet on atherosclerosis may be explained by the enhancement of high-density lipoprotein-cholesterol levels and the impairment of low-density lipoprotein-cholesterol levels, the low-density lipoprotein susceptibility to oxidation, cellular oxidative stress, thrombogenicity and atheroma plaque formation. On the other hand, the increase of high-density lipoprotein cholesterol levels and the reduction of thrombogenicity, atheroma plaque formation and vascular smooth muscle cell proliferation may account for the beneficial effects of polyunsaturated fatty acid on the prevention of atherosclerosis. Thus, the advantages of the Mediterranean diet rich in olive oil and fish on atherosclerosis may be due to the modulation of the cellular oxidative stress/antioxidant status, the modification of lipoproteins and the down-regulation of inflammatory mediators.

Dietary monounsaturated versus polyunsaturated fatty acids: which is really better for protection from coronary heart disease?

PURPOSE OF REVIEW

The purpose is to evaluate recent findings concerning dietary fats and the risk of coronary heart disease. Monounsaturated fatty acids are often regarded as healthy, and many have recommended their consumption instead of saturated fatty acids and polyunsaturated fatty acids. Support for the benefits of monounsaturated fatty acids comes largely from epidemiological data, but they have not been an isolated, single variable in such studies. Beneficial effects on the plasma lipid profile and LDL oxidation rates have also been identified. More recent findings have questioned the impact of suspected beneficial effects on coronary heart disease, indicating that studies with more conclusive endpoints are needed.

RECENT FINDINGS

Human dietary studies often produce conflicting results regarding the effects of monounsaturated and polyunsaturated fatty acids on the plasma lipid profile. Monounsaturated and polyunsaturated fatty acids both appear to reduce total and LDL-cholesterol compared with saturated fatty acids; however, the effect on HDL is less clear. Lowered HDL levels in response to low-fat or polyunsaturated fatty acid diets and the decreased protection from oxidation of polyunsaturated fatty acid-enriched LDL may not indicate increased coronary heart disease risk. Several lines of evidence also suggest that polyunsaturated fatty acids may protect against atherosclerosis.

SUMMARY

Recommendations to substitute monounsaturated fatty acids for polyunsaturated fatty acids or a low-fat carbohydrate diet seem premature without more research into the effects on the development of atherosclerosis. Current opinions favoring monounsaturated fatty acids are based on epidemiological data and risk factor analysis, but are questioned by the demonstrated detrimental effects on atherosclerosis in animal models.

Dietary mono- and polyunsaturated fatty acids similarly affect LDL size in healthy men and women

The goal of this study was to investigate the effect of the dietary fat composition on LDL peak particle diameter. Therefore, we measured LDL size by gradient gel electrophoresis in 56 (30 men, 26 women) healthy participants in a controlled dietary study. First, all participants received a baseline diet rich in saturated fat for 2 wk; they were then randomly assigned to one of three dietary treatments, which contained refined olive oil [rich in monounsaturated fatty acids (MUFA), n = 18], rapeseed oil [rich in MUFA and (n-3)-polyunsaturated fatty acids (PUFA), n = 18], or sunflower oil [rich in (n-6)-PUFA, n = 20] as the principal source of fat for 4 wk. Repeated-measures ANOVA revealed a small, but significant reduction in LDL size during the oil diet phase (-0.36 nm, P = 0.012), which did not differ significantly among the three groups (P = 0.384). Furthermore, affiliation with one of the three diet groups did not contribute significantly to the observed variation in LDL size (P = 0.690). In conclusion, our data indicate that dietary unsaturated fat similarly reduces LDL size relative to saturated fat. However, the small magnitude of this reduction also suggests that the composition of dietary fat is not a major factor affecting LDL size.