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Human Nutrition and Metabolism

The Dietary -Linolenic Acid to Linoleic Acid Ratio Does Not Affect the Serum Lipoprotein Profile in Humans¹

Department of Human Biology, Maastricht University, Maastricht, The Netherlands

²To whom correspondence should be addressed. E-mail: r.mensink{at}hb.unimaas.nl.

ABSTRACT

-Linolenic acid [ALA, 18:3(n-3)] and linoleic acid [LA, 18:2(n-6)] have comparable effects on serum lipid and lipoprotein concentrations, but their effects on lipoprotein subclass distributions and particle sizes are unknown. It is also not known whether these effects are changed by the ALA:LA ratio in the diet. To address these questions, healthy subjects (n = 54) consumed a control diet providing 7% of energy (En%) as LA and 0.4 En% as ALA during a 4-wk run-in period. For the following 6 wk of intervention, each diet was consumed by 18 subjects: the control diet, a low-LA diet (3 En% LA, 0.4 En% ALA), or a high-ALA diet (7 En% LA, 1.1 En% ALA). The ALA:LA ratio for the control diet was 1:19 and was 1:7 for the other 2 diets. Compared with the control group, LDL cholesterol decreased significantly in the ALA group (–0.32 mmol/L, P = 0.024), as did total cholesterol, apolipoprotein (apo) B, and the total:HDL cholesterol ratio. None of the dietary interventions affected HDL cholesterol, apo A-1, or triacylglycerol concentrations. The decrease in total VLDL particle concentrations in the low-LA group was due mainly to a decrease in medium VLDL (–16 nmol/L, P = 0.018) and in the high-ALA group to a decrease in small VLDL (–14 nmol/L, P = 0.044). We conclude that the ALA:LA ratio does not affect the serum lipoprotein profile. Compared with the control and LA diets, ALA lowered LDL cholesterol concentrations, possibly caused by the decrease in small VLDL.

KEY WORDS: • -linolenic acid • linoleic acid • cholesterol • lipoprotein particle size • lipoprotein subfractions

A mixture of eicosapentaenoic acid [EPA,³ 20:5(n-3)] and docosahexaenoic acid [DHA, 22:6(n-3)], 2 fish-oil derived members of the (n-3) fatty acid family, decreases serum triacylglycerol (TG) concentrations (1). At the same time, LDL cholesterol concentrations may increase slightly, especially in hypertriacylglycerolemic subjects (2). On the other hand, lipoprotein particle distributions might be favorably affected (3). These effects are not shared by -linolenic acid [ALA, 18:3(n-3)], an essential fatty acid from the (n-3) family and a precursor for EPA and DHA synthesis (4). In fact, the few intervention studies on the effects of ALA on lipid metabolism indicate that ALA has effects on serum lipid concentrations similar to those of linoleic acid [LA, 18:2(n-6)], its (n-6) fatty acid counterpart (5–7). In these studies, ALA:LA ratios differed between the diets. Because the metabolism of ALA and LA are interrelated, which is particularly evident in the competition for the same elongation and desaturation enzymes, a change in this ratio might also affect lipid metabolism, independently of changes in the intake of ALA or LA. The studies conducted to date were not able to disentangle the effects on serum lipid concentrations of the ALA:LA ratio from those of the 2 individual fatty acids. Furthermore, the effects of dietary ALA, LA, and the ALA:LA ratio on lipoprotein particle sizes and subclass distributions have not been investigated together in detail. In only 1 human study, it was reported that walnuts, a source rich in both ALA and LA, decreased cholesterol concentrations preferentially in the small LDL subfractions (8). The aim of the present study therefore was to compare side-by-side the effects of ALA, LA, and the ALA:LA ratio on fasting serum lipids and apolipoproteins concentrations, and on lipoprotein particle subclasses in humans.

SUBJECTS AND METHODS

    Subjects. Subjects were recruited from Maastricht and the surrounding area through posters in public buildings and advertisements in local newspapers. Men and women (n = 90), between 18 and 65 y old, applied for enrollment in this controlled dietary intervention study. The purpose and nature of the study, as approved by the Medical Ethics Committee of Maastricht, were fully explained to all applicants. These subjects were invited for 2 screening visits after they had given their written informed consent. Subjects’ eligibility was evaluated by means of a medical questionnaire, a urine test to exclude glucosuria, and measurements of serum lipids concentrations in 2 blood samples taken while fasting; there was an interval of at least 3 d between the samples. In addition, after a 10-min rest period, 3 blood pressure measurements were obtained during the first screening visit. When mean diastolic blood pressure of the last 2 measurements was >85 or systolic > 150 mm Hg, blood pressure was measured again during the 2nd screening visit.

Of these 90 subjects, 65 met the following eligibility criteria: BMI < 30 kg/m²; stable body weight with a maximum change < 3 kg in the past 3 mo; mean serum total cholesterol < 8.0 mmol/L, mean serum TG < 2.5 mmol/L; mean diastolic and systolic blood pressure < 95 mm Hg and < 160 mm Hg, respectively; no use of medication or prescribed diets known to affect serum lipids; no glucosuria; and no history of coronary heart disease. Ten subjects, 5 men and 5 women, withdrew from the study because of moving to another area (n = 2), job commitments (n = 1), illness (n = 1), or difficulties complying with the strict study protocol (n = 6). Before data analysis, results from 1 man were excluded because of gastrointestinal illness during wk 3 and 4 of the study. Of the 54 subjects (21 men and 33 women) that completed the study, 6 women and 4 men smoked, 6 women used oral contraceptives, and 14 women were menopausal.

The 21 men that completed the study were (means ± SD) 52.6 ± 13.7 y old, had a BMI of 24.3 ± 4.4 kg/m², a systolic blood pressure of 125 ± 15 mm Hg, and a diastolic blood pressure of 78 ± 6 mm Hg. The 33 women that completed the study were 47.7 ± 11.1 y old, had a BMI of 23.9 ± 2.7 kg/m², a systolic blood pressure of 124 ± 18 mm Hg, and a diastolic blood pressure of 78 ± 9 mm Hg. For the men, the mean fasting concentrations of serum total cholesterol, LDL cholesterol, HDL cholesterol, and TG at the screening were 5.44 ± 1.11 mmol/L, 3.80 ± 1.03 mmol/L, 1.10 ± 0.23 mmol/L, and 1.16 ± 0.62 mmol/L, respectively. In women, they were 5.42 ± 1.14 mmol/L for total cholesterol, 3.49 ± 1.13 mmol/L for LDL, 1.44 ± 0.47 mmol/L for HDL, and 1.07 ± 0.58 mmol/L for TG.

    Design and diets. The study was designed as a randomized, double-blind, parallel intervention study. The total study duration comprised a period of 10 successive weeks: a run-in period of 4 wk followed by an intervention period of 6 wk. During the run-in period, all subjects consumed a control diet, which reflected the mean daily intake of the Dutch population (9). After the run-in period, subjects were randomly allocated to 1 of the 3 possible dietary intervention groups, stratified for gender, age, and total cholesterol concentrations as determined during the screening. The first group (control group, n = 18) continued to consume the control diet. This diet was made up of 7% of energy (En%) from LA and 0.4 En% from ALA, resulting in an ALA:LA ratio of 1:19. The second (low-LA group, n = 18) and the third group (high-ALA group, n = 18) followed a diet with a higher ALA:LA ratio of 1:7. Although the ALA:LA ratio was comparable between these 2 groups, the proportions of energy from LA and ALA differed. For the low-LA group, LA consumption was decreased to 3 En%, whereas ALA intake was not changed. For the high-ALA group, however, ALA intake was increased to 1.1 En%, whereas LA intake was identical to that in the control group.

The 3 study diets, each supplying 15 En% as protein, 50 En% as carbohydrates, and 35 En% as fat, were formulated at 9 levels of energy, ranging from 7.5 to 13.4 MJ. The difference between 2 successive levels was 0.84 MJ. Before the start of the study, subjects were asked to weigh and record their habitual food intakes during 2 working days and 1 weekend day. Energy intake and macronutrient composition of the habitual dietary intake were calculated using the Dutch food composition table (10). Based on the data of the food records, subjects were assigned to 1 of the 9 energy groups.

For each energy level, dietary guidelines were composed with respect to type, daily amounts, and preparation of nonexperimental food items. Subjects had to follow these guidelines strictly. Consumption of fish and other marine foods was not allowed. The nonexperimental food items supplied 10–13 En% as fat, which was equivalent to 29–38% of total fat intake. In addition, experimental products were supplied, which provided 22–25 En% as fat. These products were made from experimental fats (Supplemental Table 1). The control fat consisted of a mixture of 30.4% sunflower oil, 33.1% olive oil, 11.5% rapeseed oil, and 25% hardstock made from fully hydrogenated palm kernel and palm oil. The experimental fat low in LA was composed of 63% olive oil, 9% rapeseed oil, and 28% hardstock. The fat rich in ALA consisted of 20% sunflower oil, 5% olive oil, 52.5% rapeseed oil, and 22.5% hardstock. From these fats, a margarine was made containing 84% absorbable fats and 16% water. Both the fats and the margarines were made by NIZO food research. Volunteers were required to use the margarines for cooking, baking, and as spread on bread. In addition, a local bakery prepared pastries, such as pies, cookies, and cake from these margarines. Depending on energy intake, subjects had to consume a specific amount of experimental products on a daily (cookies, margarine for cooking and as spread) or weekly (pies and cake) basis. Each volunteer visited the department 1 time/wk to receive a new supply of experimental products.

Subjects had to fill out daily diaries in which they noted in detail any signs of illness, medication used, its date and time of occurrence, duration, and date of resolution. Furthermore, they were asked to record menstrual phase, any deviations from the protocol, and the daily amounts of products used. Each week, diaries were checked in the presence of the subjects by a registered dietician. Subjects were urged not to change the level of physical exercise, smoking habits, alcohol or oral contraceptive use during their participation in the study. Body weight of all participants was measured once a week. Whenever body weight changed by >2 kg compared with body weight at trial entry, subjects were reassigned to a different energy level. At the end of both the run-in and the intervention periods, subjects had to weigh and record their food intakes for 2 working days and 1 weekend day to estimate energy and nutrient intakes (10).

    Blood sampling and analysis. At the end of the run-in period (wk 3 and 4), as well as at the end of the intervention period (wk 9 and 10), blood samples were drawn from fasting subjects to measure concentrations of lipoprotein particles, serum lipids, apolipoprotein (apo) A-I and apoB. To determine the fatty acid composition of plasma phospholipids, a blood sample was taken at the end of wk 4 and 10. Subjects were instructed to abstain from alcohol the day before a blood sampling and not to consume any food at all at least 12 h before sampling. Tea, without sugar or milk, and water, however, were allowed. Venous blood samples were taken from the antecubital vein, under minimal stasis, with the subject in a supine position. Venipunctures were performed under standardized conditions using a 0.9 x 38-mm needle (PrecisionGlide, Becton Dickinson Vacutainer System) by the same technician, at the same location, and usually at the same time and on the same weekday for each subject.

Blood for analysis of serum lipids, apolipoproteins, lipoproteins, and their subclasses was sampled in a 10-mL clotting tube (BD Vacutainer Systems, Becton Dickinson). After blood was allowed to clot for a minimum of 1 h at room temperature, serum was obtained by centrifugation at 2000 x g for 30 min at 4°C. Serum samples were then stored in small portions at –80°C until later analysis. For determination of the fatty acid composition of plasma phospholipids, precooled EDTA tubes were used for blood collection. Within 1 h after sampling, blood was centrifuged at 2000 x g for 30 min at 4°C, and the plasma samples obtained were snap-frozen in liquid nitrogen and stored at –80°C.

Serum lipids and lipoprotein concentrations were measured separately in the serum samples from wk 3, 4, 9, and 10. Serum total cholesterol and HDL cholesterol, after precipitation of apoB-containing lipoproteins (HDL Cholesterol precipitant, Roche Diagnostics), were analyzed with the CHOD-PAP method (ABX Diagnostics). Serum concentrations of TG, also determined enzymatically, were corrected for free glycerol (GPO Trinder; Sigma Diagnostics). Serum LDL cholesterol concentrations were calculated with the Friedewald equation (11). The CV within assays was 0.9% for total cholesterol, 2.4% for HDL, and 2.3% for TG.

Serum samples of wk 3 and 4, as well as of wk 9 and 10 were pooled before analysis of apolipoproteins and lipoprotein particles. Serum concentrations of lipoprotein subclasses and lipoprotein particle sizes were measured using NMR spectroscopy (Liposcience) in a randomly chosen subgroup of 29 subjects, 15 women and 14 men (12,13). Apo A-1 and apoB concentrations were analyzed in the pooled serum samples of all participants using commercially available kits (ABX DIAGNOSTICS). The CV within assays was 1.9% for apo A-1 and 2.3% for apoB. Total lipids were extracted from plasma following a modified Folch procedure (14). Thereafter, phospholipids were isolated from total lipids using an Extract-Clean NH2-aminopropylsilyl column (500 mg, 4.0 mL; Alltech Associates) and subsequently hydrolyzed and methylated into FAMEs (15,16). Separation and quantification of the FAMEs was obtained with GC-flame ionization detection (Perkin Elmer Autosystem), using a CP-Sil 88 capillary column (50 m x 0.25 mm, 0.20-µm film thickness; Chrompack) as described previously (17). All samples from each subject were analyzed in one single assay at the end of the study.

    Statistics. The power to detect a difference in serum LDL cholesterol concentrations of 8% between 2 treatment groups with an of 0.05 was 80%. For each subject, serum lipids and lipoprotein values from wk 3 and 4, as well as from wk 9 and 10, were averaged. Results are expressed as means ± SD. Responses to the experimental diets were calculated for each subject by subtracting the value of a variable obtained at the end of the run-in period from the value at the end of the experimental period. The effects of the diets were examined with ANOVA, using the General Linear Models (GLM) procedure in SAS (SAS System release 8.2; SAS Institute). The response to the experimental diet was defined as the dependent variable and dietary group as a fixed factor. When significant differences were found (P < 0.05), a Tukey post hoc test was used to make a pair-wise comparison of the diets.

RESULTS

    Dietary intake and body weight. Changes in energy intake, the proportions of energy from protein, carbohydrate, and total fat, as well as the amounts of cholesterol and fiber, were negligible and did not differ among the 3 groups. Differences in dietary fatty acid intake were as expected (Table 1). Compared with the control group, the intake of LA was reduced in the LA group, due mainly to an exchange for oleic acid (OA) plus some SFA. In the high-ALA group, the intake of ALA was slightly increased. These dietary fatty acid changes resulted in an ALA:LA ratio of 1:19 in the control group, and of 1:7 in the 2 experimental groups.

Dietary compliance was further confirmed by changes in the fatty acid composition of plasma phospholipids (Table 2). Compared with the control group, the change in the proportion of monounsaturated fatty acids (MUFA) was increased, whereas that of LA was reduced when subjects consumed the low-LA diet. The proportions of MUFA and PUFA remained unchanged after consumption of the high-ALA diet. The changes in the proportions of total (n-3) fatty acids and of ALA and EPA were greater in the low-LA and high-ALA groups than in the control group. The proportion of docosapentaenoic acid (DPA) increased, only after consumption of the diet high in ALA. None of the 3 diets affected the proportions of SFA and of DHA in plasma phospholipids. Inspection of the diaries did not reveal any serious deviations from the protocol.

DISCUSSION

In the present study with normocholesterolemic subjects, we found that a slight increase in the intake of ALA effectively lowered LDL cholesterol. This decrease might be related to the significant decrease in the small VLDL subparticles. It has long been thought that LA lowered serum total and LDL cholesterol concentrations compared with OA (18). This conclusion was challenged by studies conducted in the late 1980s and 1990s, which demonstrated comparable effects of LA and OA on the serum lipoprotein profile (19,20). However, a recent meta-analysis indicated that LA may still lower LDL cholesterol compared with OA, although differences in effects are small (21). Our results from the control and the low-LA groups agree with these findings. When the low-LA diet was consumed, the decrease in LA was compensated by an increase in OA and a slight increase in SFA. Based on a recent meta-analysis (21), we calculated that consumption of the low-LA diet would decrease LDL cholesterol concentrations by 0.08 mmol/L compared with the control diet. Hence, the study findings concerning total LDL cholesterol concentrations are in line with expectations.

Like LA, ALA is an essential fatty acid. Intakes of ALA are much lower, however, than those of LA. On average, ALA intake varies between 1 and 2 g/d, whereas the mean daily LA intake is 15 g (22,23). Several studies with normocholesterolemic subjects suggested that an exchange of ALA for LA does not affect serum lipid concentrations. Pang et al. (6), for example, found no significant effects on the serum lipoprotein profile when LA consumption was decreased from 6.7 En% (21 g/d) to 3.1 En% (12 g/d), and ALA intake was increased simultaneously from 0.1 En% (1 g/d) to 3.5 En% (10 g/d). Mantzioris et al. (5) also found no change in serum lipid concentrations when a typical Western diet providing 7.8 En% (20.3 g/d) from LA and 0.4 En% (1.1 g/d) from ALA was replaced by a diet that supplied 3.3 En% (8.4 g/d) LA and 5.3 En% (13.7 g/d) ALA. Also, in 2 studies with hyperlipidemic subjects, comparable effects of ALA and LA on serum LDL cholesterol were reported (24,25). In our study, we increased the intake of ALA from 0.4 En% (1.1 g/d) to 1.1 En% (3.1 g/d) at the expense of some LA, OA, and SFA. The slight decrease in total fat intake of 0.7 En% was compensated mainly by a slight increase in protein intake. If ALA and LA would indeed have comparable effects on serum LDL cholesterol, then a difference of 0.04 mmol/L between the control and high-ALA groups could be expected (21). In fact, a significant difference of 0.32 mmol/L was observed in favor of the high-ALA group. This result does not agree with findings from previous studies (5–7,26,27). The question then arises whether this is a chance finding or whether it can be explained by differences among studies in experimental design.

The metabolisms of ALA and LA are mutually dependent, as shown by the competition for the same elongation and desaturation enzymes (28–30). In most studies conducted to date, the intakes of LA and ALA, and consequently their ratio, changed at the same time. The present study was therefore specifically designed to disentangle the effects of the ALA:LA ratio on the serum lipid profile from those of the absolute amounts of ALA and LA in the diet. The low-LA and high-ALA diets had a comparable ALA:LA ratio of 1:7, which was much higher than the ratio of 1:19 of the control diet. Despite similar ALA:LA ratios, serum LDL cholesterol concentrations were significantly lowered only in the high-ALA group. This suggests that the ALA:LA ratio itself does not affect serum LDL cholesterol concentrations. The finding that the ALA:LA ratio is not important implies that the increase in dietary ALA should have caused the observed decrease in LDL cholesterol. Yet, the increase in ALA intake was rather small compared with studies that did not demonstrate a difference in the effect on LDL cholesterol between ALA and LA (5,6,27). It can also be argued that the relatively high-LA intake, which was 7 En% in the high-ALA group, modulated the effects of ALA. However, similar effects of LA and ALA on LDL cholesterol were found independently of LA intake (5–7,26). In fact, Valsta et al. (7) explicitly concluded that in the presence of considerable amounts of LA in the diet, ALA affects serum lipoprotein levels similarly to LA. Finally, we speculate that the effects of ALA do depend on the intake of cholesterol, as was postulated for palmitic acid (31). In the present study, dietary cholesterol was low for all diets and was 12.1 mg/MJ or 132 mg/d in the high-ALA diet. In this respect, it is noteworthy that in the studies of Valsta et al. (7) and Zhao et al. (25), cholesterol intake was 2 times higher. Unfortunately, the few other studies that compared the lipidemic effect of ALA and LA did not report the cholesterol levels of their diets (5,6,24,26,27). In agreement with other studies, HDL cholesterol and TG concentrations did not change significantly in our study (6,24,27).

The effects of dietary (n-3) and (n-6) fatty acids on lipoprotein particle distributions and lipoprotein particle sizes, which are related to cardiovascular risk (32–34), have scarcely been studied. For the marine PUFAs, it was suggested that fish oil may favorably lower concentrations of small and medium VLDL particles (3). Only 1 study examined changes in the lipoprotein particle profile of hyperlipidemic subjects after consuming low- and high-fat diets with and without walnuts, rich in ALA but also in LA (8). It was reported that consumption of the high-fat diet walnut supplementation favorably decreased small LDL cholesterol and large HDL particle concentrations. However, results are difficult to interpret because not only ALA and LA changed after consumption of the walnuts, but also total fat intake, which is also a determinant of lipoprotein particle size and subclass distribution (35,36), We observed a comparable decrease in total VLDL particle concentrations in the low-LA and high-ALA groups, but effects on VLDL subclasses differed. Compared with the control group, the low-LA diet decreased medium VLDL subfraction concentrations, whereas the high-ALA diet lowered small VLDL subclasses. The latter observation may explain the decrease in LDL cholesterol concentrations in the high-ALA group. Small VLDL particles, rather then large VLDL particles, are considered to be the preferred substrate for conversion into LDL lipoproteins (37,38). Hence, a decrease in small VLDL particles may lower LDL synthesis and consequently LDL cholesterol concentrations. The finding that both the low-LA and high-ALA diets decreased total VLDL particle concentrations was also observed after consumption of fish oil, which is rich in EPA and DHA (3). In the present study, the proportion of EPA in plasma phospholipids was significantly increased with consumption of both experimental diets, whereas DHA was not affected. This raises the question whether EPA might have caused the change in VLDL particle concentrations.

In conclusion, the present study indicates that the ALA:LA ratio is not a determinant of serum lipids and lipoproteins concentrations. Only the diet with a small increase in ALA intake caused a significant decrease in LDL cholesterol and apoB concentrations. This decrease might have been caused by the decrease in small VLDL particles, the precursor to LDL lipoproteins. Effects of ALA on LDL cholesterol contrasted, however, with those of previous reports and warrant further study.

ACKNOWLEDGMENTS

We gratefully acknowledge V.T.I.V.T. Ter Hercke (Herk-de-Stad, Belgium), in particular Tony Corthouts and Johny Vanden Dijck, for the production of the experimental pastries

FOOTNOTES

¹ Supplemental Tables 1–2 are available as Online Supporting Material with the online posting of this paper at www.nutrition.org.

³ Abbreviations used: ALA, -linolenic acid [18:3(n-3)]; apo, apolipoprotein; DHA, docosahexaenoic acid [22:6(n-3)]; DPA, docosapentaenoic acid [22:5(n-3)]; En%, percentage of energy; EPA, eicosapentaenoic acid [20:5(n-3)]; LA, linoleic acid [18:2(n-6)]; MUFA, monounsaturated fatty acid; TG, triacylglycerol.

Manuscript received 7 April 2005. Initial review completed 12 May 2005. Revision accepted 3 September 2005.

LITERATURE CITED

1. Harris W. S. n-3 Long-chain polyunsaturated fatty acids reduce risk of coronary heart disease death: extending the evidence to the elderly. Am. J. Clin. Nutr. 2003;77:279-280.[Free Full Text]

2. Harris W. S. Fish oils and plasma lipid and lipoprotein metabolism in humans: a critical review. J. Lipid Res. 1989;30:785-807.[Abstract]

3. Li Z., Lamon-Fava S., Otvos J., Lichtenstein A. H., Velez-Carrasco W., McNamara J. R., Ordovas J. M., Schaefer E. J. Fish consumption shifts lipoprotein subfractions to a less atherogenic pattern in humans. J. Nutr. 2004;134:1724-1728.[Abstract/Free Full Text]

4. Harris W. S. n-3 Fatty acids and serum lipoproteins: human studies. Am. J. Clin. Nutr. 1997;65:1645S-1654S.[Abstract/Free Full Text]

5. Mantzioris E., James M. J., Gibson R. A., Cleland L. G. Dietary substitution with an alpha-linolenic acid-rich vegetable oil increases eicosapentaenoic acid concentrations in tissues. Am. J. Clin. Nutr. 1994;59:1304-1309.[Abstract/Free Full Text]

6. Pang D., Allman-Farinelli M. A., Wong T., Barnes R., Kingham K. M. Replacement of linoleic acid with alpha-linolenic acid does not alter blood lipids in normolipidaemic men. Br. J. Nutr. 1998;80:163-167.[Medline]

7. Valsta L. M., Jauhiainen M., Aro A., Salminen I., Mutanen M. The effects on serum lipoprotein levels of two monounsaturated fat rich diets differing in their linoleic and -linolenic acid contents. Nutr. Metab. Cardiovasc. Dis. 1995;5:129-140.

8. Almario R. U., Vonghavaravat V., Wong R., Kasim-Karakas S. E. Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia. Am. J. Clin. Nutr. 2001;74:72-79.[Abstract/Free Full Text]

9. Zo eet Nederland. Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia. Resultaten van de voedselconsumptiepeiling 1998. Voedingscentrum, Den Haag the Netherlands.

10. Stichting Nevo. Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia. NEVO tabel, Nederlands voedingsstoffenbestand (Dutch food composition table). Voorlichtingsbureau voor de voeding Den Haag, the Netherlands.

11. Friedewald W. T., Levy R. I., Fredrickson D. S. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin. Chem. 1972;18:499-502.[Abstract]

12. Freedman D. S., Otvos J. D., Jeyarajah E. J., Shalaurova I., Cupples L. A., Parise H., D’Agostino R. B., Wilson P. W., Schaefer E. J. Sex and age differences in lipoprotein subclasses measured by nuclear magnetic resonance spectroscopy: the Framingham Study. Clin. Chem. 2004;50:1189-1200.[Abstract/Free Full Text]

13. Festa A., Williams K., Hanley A. J., Otvos J. D., Goff D. C., Wagenknecht L. E., Haffner S. M. Nuclear magnetic resonance lipoprotein abnormalities in prediabetic subjects in the Insulin Resistance Atherosclerosis Study. Circulation. 2005;111:3465-3472.[Abstract/Free Full Text]

14. Folch J., Lees M., Sloane-Stanley G. H. A simple method for the isolation and purification of total lipides from animal tissues. J. Biol. Chem. 1957;226:497-509.[Free Full Text]

15. Kaluzny M. A., Duncan L. A., Merritt M. V., Epps D. E. Rapid separation of lipid classes in high yield and purity using bonded phase columns. J. Lipid Res. 1985;26:135-140.[Abstract]

16. Lepage G., Roy C. C. Direct transesterification of all classes of lipids in a one-step reaction. J. Lipid Res. 1986;27:114-120.[Abstract]

17. Al M. D., van Houwelingen A. C., Kester A. D., Hasaart T. H., de Jong A. E., Hornstra G. Maternal essential fatty acid patterns during normal pregnancy and their relationship to the neonatal essential fatty acid status. Br. J. Nutr. 1995;74:55-68.[Medline]

18. Keys A., Anderson J. T., Grande F. Serum cholesterol response to changes in the diet IV. Particular saturated fatty acids in the diet. Metabolism. 1965;14:776-786.

19. Mattson F. H., Grundy S. M. Comparison of effects of dietary saturated, monounsaturated, and polyunsaturated fatty acids on plasma lipids and lipoproteins in man. J. Lipid Res. 1985;26:194-202.[Abstract]

20. Mensink R. P., Katan M. B. Effect of a diet enriched with monounsaturated or polyunsaturated fatty acids on levels of low-density and high-density lipoprotein cholesterol in healthy women and men. N. Engl. J. Med. 1989;321:436-441.[Abstract]

21. Mensink R. P., Zock P. L., Kester A. D., Katan M. B. Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am. J. Clin. Nutr. 2003;77:1146-1155.[Abstract/Free Full Text]

22. Sanders T. A. Polyunsaturated fatty acids in the food chain in Europe. Am. J. Clin. Nutr. 2000;71:176S-178S.[Abstract/Free Full Text]

23. Kris-Etherton P. M., Taylor D. S., Yu-Poth S., Huth P., Moriarty K., Fishell V., Hargrove R. L., Zhao G., Etherton T. D. Polyunsaturated fatty acids in the food chain in the United States. Am. J. Clin. Nutr. 2000;71:179S-188S.[Abstract/Free Full Text]

24. Finnegan Y. E., Minihane A. M., Leigh-Firbank E. C., Kew S., Meijer G. W., Muggli R., Calder P. C., Williams C. M. Plant- and marine-derived n-3 polyunsaturated fatty acids have differential effects on fasting and postprandial blood lipid concentrations and on the susceptibility of LDL to oxidative modification in moderately hyperlipidemic subjects. Am. J. Clin. Nutr. 2003;77:783-795.[Abstract/Free Full Text]

25. Zhao G., Etherton T. D., Martin K. R., West S. G., Gillies P. J., Kris-Etherton P. M. Dietary alpha-linolenic acid reduces inflammatory and lipid cardiovascular risk factors in hypercholesterolemic men and women. J. Nutr. 2004;134:2991-2997.[Abstract/Free Full Text]

26. Bemelmans W. J., Broer J., Feskens E. J., Smit A. J., Muskiet F. A., Lefrandt J. D., Bom V. J., May J. F., Meyboom-de Jong B. Effect of an increased intake of alpha-linolenic acid and group nutritional education on cardiovascular risk factors: the Mediterranean Alpha-linolenic Enriched Groningen Dietary Intervention (MARGARIN) study. Am. J. Clin. Nutr. 2002;75:221-227.[Abstract/Free Full Text]

27. Kelley D. S., Nelson G. J., Love J. E., Branch L. B., Taylor P. C., Schmidt P. C., Mackey B. E., Iacono J. M. Dietary -linolenic acid alters tissue fatty acid composition, but not blood lipids, lipoproteins or coagulation status in humans. Lipids. 1993;28:533-537.[Medline]

28. Brenna J. T. Efficiency of conversion of alpha-linolenic acid to long chain n-3 fatty acids in man. Curr. Opin. Clin. Nutr. Metab. Care. 2002;5:127-132.[Medline]

29. Sinclair A. J., Attar-Bashi N. M., Li D. What is the role of -linolenic acid for mammals?. Lipids. 2002;37:1113-1123.[Medline]

30. Gerster H. Can adults adequately convert alpha-linolenic acid (18:3n-3) to eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3)?. Int. J. Vitam. Nutr. Res. 1998;68:159-173.[Medline]

31. Hayes K. C., Khosla P. Dietary fatty acid thresholds and cholesterolemia. FASEB J. 1992;6:2600-2607.[Abstract]

32. Freedman D. S., Otvos J. D., Jeyarajah E. J., Barboriak J. J., Anderson A. J., Walker J. A. Relation of lipoprotein subclasses as measured by proton nuclear magnetic resonance spectroscopy to coronary artery disease. Arterioscler. Thromb. Vasc. Biol. 1998;18:1046-1053.[Abstract/Free Full Text]

33. Tulenko T. N., Sumner A. E. The physiology of lipoproteins. J. Nucl. Cardiol. 2002;9:638-649.[Medline]

34. Rosenson R. S., Otvos J. D., Freedman D. S. Relations of lipoprotein subclass levels and low-density lipoprotein size to progression of coronary artery disease in the Pravastatin Limitation of Atherosclerosis in the Coronary Arteries (PLAC-I) trial. Am. J. Cardiol. 2002;90:89-94.[Medline]

35. Campos H., Dreon D. M., Krauss R. M. Associations of hepatic and lipoprotein lipase activities with changes in dietary composition and low density lipoprotein subclasses. J. Lipid Res. 1995;36:462-472.[Abstract]

36. Dreon D. M., Fernstrom H. A., Miller B., Krauss R. M. Low-density lipoprotein subclass patterns and lipoprotein response to a reduced-fat diet in men. FASEB J. 1994;8:121-126.[Abstract]

37. Lu G., Windsor S. L., Harris W. S. Omega-3 fatty acids alter lipoprotein subfraction distributions and the in vitro conversion of very low density lipoproteins to low density lipoproteins. J. Nutr. Biochem. 1999;10:151-158.[Medline]

38. Packard C. J., Munro A., Lorimer A. R., Gotto A. M., Shepherd J. Metabolism of apolipoprotein B in large triglyceride-rich very low density lipoproteins of normal and hypertriglyceridemic subjects. J. Clin. Investig. 1984;74:2178-2192.[Medline]

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