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European Journal of Clinical Nutrition (1998) 52, 728±732 ß 1998 Stockton Press. All rights reserved 0954±3007/98 $12.00 http://www.stockton-press.co.uk/ejcn The effect of a low-fat, high-carbohydrate diet on serum high density lipoprotein cholesterol and triglyceride ML Turley1, CM Skeaff1, JI Mann1 and B Cox2 1 Department of Human Nutrition, University of Otago, PO Box 51, Dunedin, New Zealand; and 2Department of Preventive & Social Medicine, University of Otago, PO Box 51, Dunedin, New Zealand Objective: To determine whether substituting carbohydrate for saturated fat has any adverse effects on serum high density lipoprotein (HDL) cholesterol and triglycerides in free-living individuals. Design: Randomised crossover trial. Setting: General community. Subjects: Volunteer sample of 38 healthy free-living men with mean (s.d.) age 37 (7) y, moderately elevated serum total cholesterol 5.51 (0.93) mmol=l and body mass index 26.0 (3.6) kg=m2. Interventions: Participants completed two six week experimental periods during which they consumed either a traditional Western diet (36%, 18%, and 43% energy from total, saturated, and carbohydrate, respectively) or a low-saturated fat high-carbohydrate diet (22%, 6% and 59% energy from total, saturated, and carbohydrate, respectively). Dietary principles were reinforced regularly, but food choices were self-selected during each experimental period. Main outcome measures: Serum lipids, body weight and plasma fatty acids. Results: Reported energy and nutrient intakes, plasma fatty acids, and a drop in weight from 79.1 (12.5) kg on the Western diet to 77.6 (12.0) kg on the high-carbohydrate diet (P < 0.001) con®rmed a high level of compliance with experimental diets. Total and low density lipoprotein (LDL) cholesterol fell from 5.52 (1.04) mmol=l and 3.64 (0.88) mmol=l, respectively on the Western diet to 4.76 (1.10) mmol=l and 2.97 (0.94) mmol=l on the high-carbohydrate diet (P < 0.001). HDL cholesterol fell from 1.21 (0.27) mmol=l on the Western diet to 1.07 (0.23) mmol=l on the high-carbohydrate diet (P 0.057), but the LDL:HDL cholesterol ratio improved from 3.17 (1.05) on the Western diet to 2.88 (0.97) on the high-carbohydrate diet (P 0.004). Fasting triglyceride levels were unchanged throughout the study. Conclusions: Replacement of saturated fat with carbohydrate from grains, vegetables, legumes, and fruit reduces total and LDL cholesterol with only a minor effect on HDL cholesterol and triglyceride. It seems that when free living individuals change to a ®bre rich high-carbohydrate diet appropriate food choices lead to a modest weight reduction. This may explain why the marked elevation of triglyceride and reduction of HDL cholesterol observed on strictly controlled high-carbohydrate diets may not occur when such diets are followed in practice. Sponsorship: New Zealand Lottery Health Research. Descriptors: diet; saturated fat; carbohydrate; lipoproteins; triglyceride Introduction The risk of coronary heart disease increases in a continuous and graded manner across the entire distribution of serum cholesterol concentrations (Multiple Risk Factor Intervention Trial Research Group, 1982; La Rosa et al, 1990; Chen et al, 1991; Verschuren et al, 1995). Given that coronary disease continues to be a leading cause of morbidity and mortality in developed countries, the reduction of serum cholesterol concentrations has become a major public health objective, and the target for both individuals and populations is a cholesterol concentration of 5.2 mmol=l (Assmann, 1990; Bettridge et al, 1993; Mann et al, 1993; NCEP Expert Panel, 1993). The individual, or high risk approach, targets those with the highest blood cholesterol concentrations; however, because a small proportion of the Correspondence: Dr CM Skeaff. Received April 2 1998; revised May 25 1998; accepted June 9 1998 population falls into this category the overall impact on coronary heart disease mortality is relatively small. To reduce coronary heart disease mortality at a population level, it is essential to shift the entire distribution of cholesterol concentrations to a range where the risk of the disease is much lower, and this is best achieved by targeting those with moderately elevated cholesterol as they account for the greatest number of coronary heart disease deaths (Assmann, 1990). The in¯uences of dietary fat on serum cholesterol have been studied extensively, and there is universal agreement that a reduction in dietary saturated fat will lower serum total and low density lipoprotein (LDL) cholesterol (Grundy & Denke, 1990; La Rosa et al, 1990; Mensink & Katan, 1992; Hegsted et al, 1993; NCEP Expert Panel, 1993; Katan et al, 1994). There is, however, no agreement as to which nutrients should replace saturated fatty acids. Some authorities recommend that cis-mono and polyunsaturated fats should replace saturated and trans-unsaturated fatty acids (Katan et al, 1997), while others argue that The effect of a low-fat, high-carbohydrate diet ML Turley et al carbohydrate from grains, legumes, vegetables and fruit should replace a substantial proportion of the saturated fat in the diet (Connor & Connor, 1997). A pivotal issue underlying this debate is whether or not high-carbohydrate diets induce hypertriglyceridaemia and reduce high density lipoprotein (HDL) cholesterol concentrations. In this present study we compared the effects of highand low-saturated fat diets on blood lipids, lipoproteins and fatty acids to determine the extent to which a self-selected, low-saturated fat diet will favourable in¯uence total and LDL cholesterol in men with moderately elevated cholesterol; and secondly, to investigate whether substituting carbohydrate for dietary saturated fat has any adverse effect on HDL cholesterol or fasting triglyceride. Materials and methods Subjects Thirty-eight subjects aged 23 ± 49 y were recruited by advertising in the local Dunedin area. After explanation of the study aim and protocol, subjects gave written consent to participate. Two subjects were unable to complete the protocol due to work commitments out of the region, and results relating to them have been excluded. The thirty six subjects who successfully completed the study were healthy free-living males, mean (s.d.) age 37 (7) y, with a body mass index (BMI) of 26.0 (3.6) kg=m2. This research was approved by the Ethics Committee of the Southern Regional Health Authority (Dunedin, New Zealand). Experimental design Subjects were asked to consume their usual diet for a two week run-in period, during which they recorded their food and beverage intake for seven days (to minimise recording fatigue: 4 d recording, 7 d off, 3 d recording). Subjects were then randomly assigned to either a Western diet high in saturated fat or a low-fat high-carbohydrate diet. After six weeks subjects returned to their usual diet for one week before crossing over to the alternate diet for a further six weeks. Subjects were advised to continue their regular pattern of physical activity for the duration of the study. Blood measurements were made at the end of the run-in period (baseline) and at weeks ®ve and six of each diet period. For practical reasons, the study was conducted in two phases: the ®rst involving 14 subjects and the second 22 subjects. Diets The Western and high-carbohydrate diets were designed to be isoenergetic, provide 40% and 25% of energy from fat, and 45% and 60% of energy from carbohydrate, respectively. Both diets provided 14% of energy from monounsaturated fat, and 6% of energy from polyunsaturated fat, with saturated fat providing the remaining 20% and 5% of energy on the Western and high-carbohydrate diets, respectively. Participants were given dietary advice at the beginning of each intervention period, and received a booklet containing instructions and recipes suitable for each of the experimental diets. The Western diet was designed to be similar to the traditional New Zealand diet, and as such participants were advised to use butter and=or lard for cooking, spreading and baking, to consume full-fat milk and cheese, and to eat meat at least ®ve times a week. On the high-carbohydrate diet participants were advised to replace saturated fat with carbohydrate-rich foods such as fruit, vegetables, breads, cereals, and grains, to use olive oil and low-fat spreads sparingly, to consume low-fat milk and cheese, and to eat lean meat no more than twice a week. Participants were also advised not to use polyunsaturated margarines and oils, nuts (except hazelnuts and almonds), commercial cakes, biscuits, and deep fried foods. Butter and lard or olive oil and low-fat spreads were provided for the participants when following the corresponding experimental diet. Body weight was measured every two weeks and subjects who were losing or gaining weight were advised to adjust their energy intake accordingly. To assess dietary compliance food intake was recorded for seven days, as per the run in period, during each experimental diet. Nutrient composition was determined using `Diet Entry and Storage' and `Diet Cruncher' which uses food composition data from the New Zealand Institute for Crop and Food Research Ltd. Laboratory methods After an overnight fast of at least 12 h, venous blood was collected into vacutainers containing disodium EDTA (for fatty acid analysis) or no anticoagulant (for cholesterol analysis). Plasma and serum were separated by centrifugation at 1500 g for 15 min, and aliquots were stored in plastic tubes at 7 20 C and 7 80 C, respectively. Cholesterol and triglyceride concentrations in serum were measured by enzymatic kits from Boehringer-Mannheim and Roche Diagnostics on a Cobas Fara Analyser (Roche Diagnostics). HDL cholesterol was measured in the supernatant following precipitation of apoB-containing lipoproteins with phosphotungstate-magnesium (Assmann et al, 1983). LDL cholesterol was calculated using the Friedewald formula (Friedewald et al, 1972). Serum samples from each participant were analysed in the same batch to remove the effects of between batch variation. The within batch coef®cient of variation was 1.6% for cholesterol, and 2.7% for triglyceride, and these assays were validated according to the Royal Australasian College of Pathologists Quality Assurance Program. Plasma lipids were extracted according to the method of Bligh & Dyer (1959). Triglycerides were separated by spotting lipid extracts onto silica gel 60 (Merck) thinlayer chromatography plates and running in a solvent system of hexane:diethyl ether:acetic acid (85:15:1). Lipid bands were visualised under UV light after spraying with 0.1% ANS (8-anilino-1-napthalene sulfonic acid), and identi®cation veri®ed by using commercial standards. Lipid bands were scraped into glass tubes and methylated at 80 C with 6% H2SO4 in methanol for 2 h, then eluted into hexane and stored at 7 18 C. Separation of the fatty acid methyl esters from triglycerides was achieved using a DB-225 megabore column (25 m60.53 mm internal diameter; ®lm thickness 0.25 mm; J & W Scienti®c) installed on a HP5890 Series II Gas Chromatograph with ¯ame ionisation detection. The oven was operated isothermally at 200 C, with the injector and detector both at 250 C. Helium was used as the carrier gas with the inlet pressure 60 kPa, and split ratio 4:1. Fatty acid peaks were identi®ed by matching retention times with authentic fatty acid standards (NuCheck Prep). The addition of an internal standard to samples and blanks (water) permitted the sample fatty acid peak areas to be corrected for background contamination. Fatty acid peak areas were calculated as mol% of total fatty acids. Total saturated, monounsaturated, and polyunsaturated fatty 729 The effect of a low-fat, high-carbohydrate diet ML Turley et al 730 acids were calculated by summing all individual fatty acids, including some not reported in the tables because they were less than 1 mol%. The precision of fatty acid measurement was determined by repeated analysis of pooled plasma. The coef®cients of variation for fatty acids contributing greater than 1 mol% in triglycerides were as follows: C14:0, 10.9%; C16:0, 1.9%; C18:0, 4.0%; C16:1, 3.7%; C18:1, 2.2%; C18:2n-6, 3.0%; C20:4n-6, 5.6%; C18:3n-3, 4.4%. For fatty acids contributing less than 1 mol% the coef®cients of variation were as follows: C20:5n-3, 5.2%; C22:6n-3, 10.5%. Statistical analysis Statistical analyses were carried out using SPSS-X release 4.0.1. Serum lipid measurements made during weeks ®ve and six were not signi®cantly different (student's t-test), and the mean of the two values was used to provide a more reliable measure. Differences between measurements made on the two experimental diets were compared by repeated measures=analysis of covariance, with baseline values as the covariate. As part of the analysis the effect of diet sequence was tested, and for those variables where there was a sequence effect only data from the ®rst arm of the crossover were compared. Results were considered statistically signi®cant when P values were less than 0.05. Results The energy and nutrient composition of the baseline, Western, and high-carbohydrate diets, as calculated from the diet records, are shown in Table 1. The fourteen energy percent lower total fat content of the high-carbohydrate diet was very close to our target difference of ®fteen energy percent. Saturated fat intake was three-fold higher on the Western diet. The ratio of polyunsaturated to saturated fat (P:S) was almost ®ve times higher on the high-carbohydrate diet. The drop in energy provided by fat on the highcarbohydrate diet was offset by the increased carbohydrate content of the diet. Despite efforts to keep energy intake constant on the experimental diets, the high-carbohydrate diet provided 1940 kJ (462 kcal) less energy than the Western diet. The average decrease in body weight on the high-carbohydrate diet was 1.5 kg (Table 2). Total cholesterol was 0.76 mmol=l lower on the highcarbohydrate diet (Table 3). The decrease in total cholesterol was largely explained by a 20%, or 0.67 mmol=l decrease in LDL cholesterol. High density lipoprotein cholesterol decreased 0.14 mmol=l on the high-carbohydrate diet (P 0.057), but the ratio of LDL to HDL cholesterol improved signi®cantly (P 0.004). The effect of the diets on plasma cholesterol concentrations was not altered by statistical adjustment for body weight. The fatty acid composition of plasma triglycerides was determined for phase two participants (n 22), and the results presented in Table 4. In triglycerides, total saturated fatty acids were 5.3 mol% lower on the high-carbohydrate diet, made up of a 0.7 mol%, 3.1 mol%, and 1.2 mol% decrease in myristic, palmitic, and stearic acid, respectively. These decreases were offset by a 4.7 mol% increase in linoleic acid. Discussion The present study contributes to understanding of the effects of diet on serum lipids in two important ways. Firstly, it is clear that a self-selected, low-saturated fat diet can lower serum total and LDL cholesterol concentrations in men with `average' cholesterol levels to an extent that could markedly reduce their risk of coronary heart disease. Secondly, our data show that replacing two-thirds of dietary saturated fat with carbohydrate has little effect on HDL cholesterol or fasting triglycerides and improves the LDL to HDL cholesterol ratio. The effects of low-saturated fat diets on serum cholesterol have been the subject of extensive research; however, Table 2 Age, height, body weight and body mass index (BMI) Experimental diets Baseline Age (y) Height (m) Weight (kg) BMI (kg/m2) 37 1.76 80.3 26.0 (7) (0.07) (12.6) (3.6) Western High-carbohydrate Pa 79.1 (12.5) 25.6 (3.7) 77.6 (12.0) 25.2 (3.5) < 0.001 < 0.001 Values are mean (s.d.); n 36. repeated measures ANOVA with baseline as covariate. a Table 1 Energy and nutrient composition of the diets Experimental diets Baseline Energy (MJ) Total fat (% energy) Saturated (% energy) Monounsatured (% energy) Polyunsaturated (% energy) Carbohydrate (% energy) Mono & disaccharides (% energy) Polysaccharides (% energy) Protein (% energy) Alcohol (% energy) Dietary ®bre (g)b Cholesterol (mg) P:S ratio 11.9 35 15 12 5 46 19 27 15 4 28 343 0.3 (2.6) (7) (4) (3) (2) (7) (6) (5) (2) (6) (9) (140) (0.1) Western 11.4 36 18 11 3 43 17 26 16 4 22 415 0.2 (2.2) (7) (4) (2) (1) (6) (6) (4) (3) (6) (6) (140) (0.1) High-carbohydrate 9.5 22 6 9 5 59 24 35 15 5 40 167 0.9 (2.3) (7) (3) (3) (1) (8) (9) (6) (3) (6) (15) (93) (0.4) Pa < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 < 0.001 0.010 ns < 0.001 < 0.001 < 0.001 Values are mean (s.d.); n 36, except for low-saturated fat diet where n 35. Abbreviations: P:S, polyunsaturated:saturated; % energy, percentage energy; ns, not signi®cant. a Repeated measures ANOVA with baseline as covariate. b Data from ®rst dietary period only because of carry-over effects from the ®rst to second treatment. The effect of a low-fat, high-carbohydrate diet ML Turley et al Table 3 731 Serum cholesterol and triglyceride concentrations (mmol=l) Experimental diets Baseline Total cholesterol LDL cholesterol HDL cholesterolb LDL:HDL Triglycerides 5.51 3.61 1.26 3.03 1.41 Western (0.93) (0.82) (0.31) (0.96) (0.68) 5.52 3.64 1.21 3.17 1.48 (1.04) (0.88) (0.27) (1.05) (0.74) High-carbohydrate 4.76 2.97 1.07 2.88 1.57 (1.10) (0.94) (0.23) (0.97) (0.69) Pa < 0.001 < 0.001 0.057 0.004 ns Values are mean (s.d.); n 36. Abbreviations: LDL, low density lipoprotein; HDL, high density lipoprotein. a Repeated measures ANOVA with baseline as covariate. b Data from ®rst dietary period only because of carry-over effects from the ®rst to second treatment. Table 4 Fatty acid composition (mol%) of plasma triglyceride Experimental diets Fatty acid C14:0 C16:0 C18:0 C16:1 C18:1 C18:2n-6 C20:4n-6 C18:3n-3 C20:5n-3 C22:6n-3 Total SFA Total MUFA Total PUFA Baseline 2.9 28.0 4.6 4.9 37.2 13.1 1.0 1.1 0.2 0.4 36.5 42.8 17.7 (1.1) (2.7) (1.9) (1.2) (3.8) (5.0) (0.5) (0.4) (0.1) (0.3) (4.5) (4.2) (6.0) Western 3.1 29.9 4.9 5.2 38.2 9.7 0.9 0.9 0.2 0.4 38.9 44.0 13.7 (1.4) (3.4) (1.7) (1.3) (4.1) (2.9) (0.3) (0.2) (0.1) (0.2) (5.0) (3.9) (3.4) High-carbohydrate 2.4 26.8 3.7 5.4 38.8 14.4 1.0 0.9 0.2 0.4 33.6 44.8 18.7 (1.1) (3.3) (1.8) (1.7) (3.6) (5.1) (0.5) (0.3) (0.1) (0.2) (5.4) (4.5) (5.8) Pa 0.027 < 0.001 0.039 ns ns < 0.001 ns ns ns ns < 0.001 ns < 0.001 Values are mean (s.d.); n 22. Abbreviations: SFA, saturated fatty acids; MUFA, monounsaturated fatty acids; PUFA, polyunsaturated fatty acids; ns, not signi®cant. a Repeated measures ANOVA with baseline as covariate. most of this research has been conducted in subjects who were hypercholesterolemic. In those with average or moderately elevated cholesterol concentrations few studies involving natural foods have been conducted outside of metabolic wards; and when they have, participants have been provided with prepared foods (Mensink & Katan, 1989; Ginsberg et al, 1990; Valsta et al, 1992; Wahrburg et al, 1992; Lichtenstein et al, 1993) or intensive dietary counselling (Ehnholm et al, 1984). A strength of the present study is that it was conducted under normal living conditions, and apart from simple dietary guidelines, subjects were free to select and prepare their own foods. Assessing dietary compliance in a free living population is often dif®cult. Participants in the present study reported energy and macronutrient intakes that were extremely close to the target intakes. Con®dence in the accuracy of the dietary assessment is increased by the fact that the lower energy intakes reported by participants while on the highcarbohydrate diet was re¯ected in a mean weight loss of 1.5 kg. Further con®rmation that compliance was high stems from changes in fatty acid composition of plasma triglycerides that parallel the reported changes in dietary fat consumption. On the basis of the diet records, accompanying weight loss on the high-carbohydrate diet, and plasma fatty acid changes, subject compliance was extremely good. The 0.76 mmol=l difference in total cholesterol between the high- and low-saturated fat diets was similar to the predicted difference based on the equations of Keys et al, (1965), Hegsted et al (1965), and Clarke et al (1997) [0.93, 1.11, and 0.93 mmol=l, respectively]. Given that the two experimental diets contained similar proportions of monounsaturated and polyunsaturated fats, and that adjustment for the weight loss on the high-carbohydrate diet had no appreciable effect on the cholesterol results, it is reasonable to conclude that the cholesterol lowering effect of the lowsaturated fat diet was due primarily to the reduced saturated fat content. This reduction in total cholesterol is comparable with that seen in a study by Mensink & Katan (1987) when a ®bre-rich carbohydrate diet, virtually identical to ours, replaced saturated fat in an equally similar Western diet. The argument against recommending carbohydrate as a source of replacement energy for saturated fat hinges largely on observations in three studies undertaken by Grundy and colleagues (Grundy, 1986; Grundy et al, 1986) and by Mensink & Katan (1987). These studies indicate that high-carbohydrate diets are associated with an increase in triglycerides and a reduction in HDL cholesterol. As a result, these authors argue strongly in favour of replacing saturated fats with non-hydrogenated unsaturated plant oils (Katan et al, 1997), an argument which is supported by observations in epidemiological studies; for example, the low coronary heart disease rates in people consuming the Mediterranean diet (Kushi et al, 1995). However, in the present study we found little deleterious effect of substituting carbohydrate for saturated fat in respect to either triglyceride or HDL cholesterol. Indeed, the high-carbohydrate diet was associated with a favourable ratio of LDL to HDL cholesterol. The most likely explanation for the discrepancy in these observations would seem to be the difference in experimental design. The studies by Grundy and colleagues involved either formula diets (Grundy, 1986), or whole food diets fed to a small number of institutionalised patients (Grundy et al, 1986). In the study by Mensink & Katan (1987) whole foods were consumed and the subjects were not institutionalised; however, main meals were prepared and served to participants in a controlled environment and virtually all other foods were provided. These diets were strictly controlled to ensure energy balance and minimise weight changes. In the present study, subjects were given clear instructions regarding appropriate food choices but were intentionally given free rein with regard to quantities in order to mimic the likely consequences in a community setting. Despite fortnightly reminders to increase energy intake if they were losing weight, participants' freedom to choose food quantities combined with the satiety enhancing effect of the foods chosen (Rolls, 1995) resulted in the modest weight reduction observed. This in turn may The effect of a low-fat, high-carbohydrate diet ML Turley et al 732 explain why the bene®cial effect of LDL-lowering from a self selected high-carbohydrate diet, as tested in this study, was not offset by any adverse changes in other lipid and lipoprotein cardiovascular risk indicators. Furthermore, the small weight loss substantiates reports that high-carbohydrate diets help to reduce obesity in free-living individuals (Toubro & Astrup, 1997). Conclusions In summary, we have demonstrated that a self-selected diet, low in saturated fat and high in carbohydrate, substantially lowers both total and LDL cholesterol, and has little adverse effect on HDL cholesterol or fasting triglyceride. The effectiveness of this diet under normal living conditions suggests that a recommendation to replace up to twothirds of dietary saturated fat with carbohydrate could shift the distribution of blood cholesterol concentrations in the population to a range where the risk of coronary heart disease was substantially lower. Therefore, ®bre-rich carbohydrate containing foods (including grains, vegetables, legumes, and fruit) or non-hydrogenated unsaturated plant oils may be substituted for saturated fatty acids. Local practice or personal preference may determine whether one foodstuff should predominate. When advice is given to individuals, the potential bene®ts of high-carbohydrate high-®bre diets to facilitate weight loss and of diets high in cis-monounsaturated fatty acids to maintain HDL levels should be taken into account. Acknowledgements ÐThe authors gratefully acknowledge the cooperation of the participants, and are indebted to Anne-Louise Heath for conducting phase 1 of the study and assisting with the design of the diets, Dr Madeleine Ball for helping design the study and obtaining ®nancial support, Margaret Waldron for her help with participants, Alex Chisholm for assisting with the design of the diets, and Peter Herbison for his expert statistical advice. References Assmann G (1990): At what levels of total and low- or high-density lipoprotein cholesterol should diet=drug therapy be initiated? European Guidelines. Am. J. Cardiol. 65, 11 ± 15. Assmann G, Schriewer H, Schmitz G & Hagele E-O (1983): Quanti®cation of high-density-lipoprotein cholesterol by precipitation with phosphotungstic acid=MgCl2. Clin. Chem. 29, 2026 ± 2030. Bettridge DJ, Dodson PM, Durrington PN, Hughes EA, Laker MF, Nicholls DP, Rees JAE, Seymour CA, Thompson GR, Winder AF, Winocour PH & Wray R (1993): Management of hyperlipidaemia: guidelines of the British Hyperlipidaemia Association. Postgrad. Med. J. 69, 359 ± 369. Bligh DG & Dyer WJ (1959): A rapid method of total lipid extraction and puri®cation. Can. J. Biochem. Physiol. 37, 911 ± 917. Chen Z, Peto R, Collins R, MacMahon S, Lu J & Li W (1991): Serum cholesterol concentration and coronary heart disease in a population with low serum cholesterol concentrations. BMJ 303, 276 ± 282. Clarke R, Frost C, Collins R, Appleby P & Peto R (1997): Dietary lipids and blood cholesterol: quantitative meta-analysis of metabolic ward studies. BMJ 314, 112 ± 117. Connor WE & Connor SL (1997): Should a low-fat, high-carbohydrate diet be recommended for everyone? The case for a low-fat, highcarbohydrate diet. N. Engl. J. Med. 337, 562 ± 563. Ehnholm C, Huttunen JK, Pietinen P, Leino U, Mutanen M, Kostianinen E, Iacono JM, Dougherty R & Puska P (1984): Effect of a diet low in saturated fatty acids on plasma lipids, lipoproteins, and HDL subfractions. Arteriosclerosis 4, 265 ± 269. Friedewald WT, Levy RI & Fredrickson DS (1972): Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin. Chem. 18, 499 ± 502. Ginsberg HN, Barr SL, Gilbert A, Karmally W, Deckelbaum R, Kaplan K, Ramakrishnan R, Holleran S & Dell RB (1990): Reduction of plasma cholesterol levels in normal men on an American Heart Association Step 1 Diet or a Step 1 Diet with added monounsaturated fat. N. Engl. J. Med. 322, 574 ± 579. Grundy SM (1986): Comparison of monounsaturated fatty acids and carbohydrates for lowering plasma cholesterol. N. Eng. J. Med. 314, 745 ± 748. Grundy SM & Denke MA (1990): Dietary in¯uences on serum lipids and lipoproteins. J. Lipid Res. 31, 1149 ± 1172. Grundy SM, Whelan MF & Franklin L (1986): Comparison of three cholesterol-lowering diets in normolipidemic men. JAMA 256, 2351 ± 2355. Hegsted DM, Ausman LM, Johnson JA & Dallal GE (1993): Dietary fat and serum lipids: an evaluation of the experimental data. Am. J. Clin. Nutr. 57, 875 ± 883. Hegsted DM, McGandy RB, Myers ML & Stare FJ (1965): Quantitative effects of dietary fat on serum cholesterol in man. Am. J. Clin. Nutr. 17, 281 ± 295. Katan MB, Grundy SM & Willett WC (1997): Should a low-fat, highcarbohydrate diet be recommended for everyone? Beyond low fat diets. N. Engl. J. Med. 337, 563 ± 567. Katan MB, Zock PL & Mensink RP (1994): Effects of fats and fatty acids on blood lipids in humans: an overview. Am. J. Clin. Nutr. 60, 1017S ± 1022S. Keys A, Anderson JT & Grande F (1965): Serum cholesterol response to changes in the diet. IV. Particular saturated fatty acids in the diet. Metabolism 14, 776 ± 787. Kushi LH, Lenart EB & Willett WC (1995): Health implications of Mediterranean diets in light of contemporary knowlege: 2. Meat, wine, fats, and oils. Am. J. Clin. Nutr. 61, 1416S ± 1427S. La Rosa JC, Hunninghake D, Bush D, Croqio MH, Getz GS & Gotto AM (1990): The cholesterol facts. A summary of the evidence relating dietary fats, serum cholesterol, and coronary heart disease. A joint statement by the American Heart Association and the National Heart, Lung, and Blood Institute. The Task Force on Cholesterol Issues, American Heart Association. Circulation 81, 1721 ± 1733. Lichtenstein AH, Ausman LM, Carrasco W, Jenner JL, Gualtieri LJ, Goldin BR, Ordovas JM & Schaefer EJ (1993): Effects of canola, corn, and olive oil on fasting and postprandial plasma lipoproteins in humans as part of a National Cholesterol Education Program Step 2 Diet. Arterioscler. Thromb. 13, 1533 ± 1542. Mann JI, Crooke M, Rear H, Hay DR, Jackson RT, Neutze JM & White HD (1993): Guidelines for the detection and management of dyslipidaemia. N. Z. Med. J. 106, 133 ± 142. Mensink RP & Katan MB (1987): Effect of monounsaturated fatty acids versus complex carbohydrates on high-density lipoproteins in healthy men and women. Lancet 1 (8525), 122 ± 125. Mensink RP & Katan MB (1989): 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. Eng. J. Med. 321, 436 ± 441. Mensink RP & Katan MB (1992): Effect of dietary fatty acids on serum lipids and lipoproteinsÐa meta-analysis of 27 trials. Artrioscler. Thromb. 12, 911 ± 919. Multiple Risk Factor Intervention Trial Research Group (1982): Multiple risk factor intervention trial: Risk factor changes and mortality results. JAMA 248, 1465 ± 1477. NCEP Expert Panel (1993): Summary of the second report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel II). JAMA 269, 3015 ± 3023. Rolls BJ (1995): Carbohydrates, fats, and satiety. Am. J. Clin. Nutr. 61, 960S ± 967S. Toubro S & Astrup A (1997): Randomised comparison of diets for maintaining obese subjects' weight after major weight loss: ad lib, low fat, high carbohydrate vs ®xed energy intake. BMJ 314, 29 ± 34. Valsta LM, Jauhiainen M, Aro A, Katan MB & Mutanen M (1992): Effects of a monounsaturated rapeseed oil and a polyunsaturated sun¯ower oil diet on lipoprotein levels in humans. Arterioscler. Thromb. 12, 50 ± 57. Verschuren WMM, Jacobs DR, Bloemberg BPM, Kromhout D, Menotti A, Aravanis C, Blackburn H, Buzina R, Dontas AS, Fidanza F, Karvonen MJ, Nedeljkovic S, Nissinen A & Toshima H (1995): Serum total cholesterol and long-term coronary heart disease mortality in different cultures. JAMA 274, 131 ± 136. Wahrburg U, Martin H, Sandkamp M, Schulte H & Assmann G (1992): Comparative effects of a recommended lipid-lowering diet vs a diet rich in monounsaturated fatty acids on serum lipid pro®les in healthy young adults. Am. J. Clin. Nutr. 56, 678 ± 683.