Hydrogenated fats in the diet and lipids in the serum of man

The Lipid-Heart Hypothesis and the Keys Equation Defined the Dietary Guidelines but Ignored the Impact of Trans-Fat and High Linoleic Acid Consumption

In response to a perceived epidemic of coronary heart disease, Ancel Keys introduced the lipid-heart hypothesis in 1953 which asserted that high intakes of total fat, saturated fat, and cholesterol lead to atherosclerosis and that consuming less fat and cholesterol, and replacing saturated fat with polyunsaturated fat, would reduce serum cholesterol and consequently the risk of heart disease. Keys proposed an equation that would predict the concentration of serum cholesterol (ΔChol.) from the consumption of saturated fat (ΔS), polyunsaturated fat (ΔP), and cholesterol (ΔZ): ΔChol. = 1.2(2ΔS - ΔP) + 1.5ΔZ. However, the Keys equation conflated natural saturated fat and industrial trans-fat into a single parameter and considered only linoleic acid as the polyunsaturated fat. This ignored the widespread consumption of trans-fat and its effects on serum cholesterol and promoted an imbalance of omega-6 to omega-3 fatty acids in the diet. Numerous observational, epidemiological, interventional, and autopsy studies have failed to validate the Keys equation and the lipid-heart hypothesis. Nevertheless, these have been the cornerstone of national and international dietary guidelines which have focused disproportionately on heart disease and much less so on cancer and metabolic disorders, which have steadily increased since the adoption of this hypothesis.

The Demise of Artificial Trans Fat: A History of a Public Health Achievement

Policy Points This article describes a strategic combination of research, advocacy, corporate campaigns, communications, grassroots mobilization, legislation, regulatory actions, and litigation against companies and government to secure a national policy to remove artificial trans fat from the US food system. Sharing lessons we learned can help inform policymakers, academics, policy practitioners, and students across disciplines. Some of our lessons are that system change means that all consumers benefit without the need for individual behavior change; research can both identify opportunities to improve health and support policy adoption; policy efforts can serve as public education campaigns; policy campaigns can drive marketplace changes; and engaging forward-thinking companies can diffuse opposition to passing a policy.

CONTEXT

For many decades, partially hydrogenated vegetable oil (PHO), the primary source of artificial trans fat in the American diet, was used widely in processed and restaurant foods. In the early 1990s, studies linked the consumption of artificial trans fat with heart disease. This article details how research and advocacy led to eliminating artificial trans fat from the US food supply.

METHODS

We synthesized published studies of the health impact of trans fat, the legislative history of state and local trans fat bills, the Food and Drug Administration's (FDA) regulatory docket on trans fat labeling and its declaration that PHOs are no longer Generally Recognized as Safe (GRAS), and our own files, which included strategy documents, notes from meetings with the FDA staff, correspondence between advocates and the FDA, fact sheets, press releases, news clips, and other materials.

FINDINGS

This history of trans fat provides insights into policy strategy and advocacy best practices that resulted in the removal of trans fat from food in the United States, preventing an estimated 50,000 premature deaths a year. The lessons we learned are that system change benefits all consumers without the need for individual behavior change; research can both identify opportunities to improve health through policy and support policy adoption; policy campaigns can serve as public education campaigns; policy can drive changes to products and the marketplace; and engaging forward-thinking companies can help diffuse opposition to passing a policy. Securing this policy required the persistence of scientists and health advocates in first discovering the risks and then using the science to secure policies to mitigate the identified harm.

CONCLUSIONS

An understanding of the tactics used to help attain the targeted policies and how challenges were addressed (such as through communications, leveraging an expanding research base and expert reports, showing that a national policy was feasible through voluntary corporate changes and state and local policy, and litigation against companies and government agencies) may provide a model for scientists, students, advocates, and policymakers. We hope this account will inform efforts to address other public health challenges, such as the current threats of excessive exposure to sodium and added sugars, which persist in the US food system.

Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73)

OBJECTIVE

To examine the traditional diet-heart hypothesis through recovery and analysis of previously unpublished data from the Minnesota Coronary Experiment (MCE) and to put findings in the context of existing diet-heart randomized controlled trials through a systematic review and meta-analysis.

DESIGN

The MCE (1968-73) is a double blind randomized controlled trial designed to test whether replacement of saturated fat with vegetable oil rich in linoleic acid reduces coronary heart disease and death by lowering serum cholesterol. Recovered MCE unpublished documents and raw data were analyzed according to hypotheses prespecified by original investigators. Further, a systematic review and meta-analyses of randomized controlled trials that lowered serum cholesterol by providing vegetable oil rich in linoleic acid in place of saturated fat without confounding by concomitant interventions was conducted.

SETTING

One nursing home and six state mental hospitals in Minnesota, United States.

PARTICIPANTS

Unpublished documents with completed analyses for the randomized cohort of 9423 women and men aged 20-97; longitudinal data on serum cholesterol for the 2355 participants exposed to the study diets for a year or more; 149 completed autopsy files.

INTERVENTIONS

Serum cholesterol lowering diet that replaced saturated fat with linoleic acid (from corn oil and corn oil polyunsaturated margarine). Control diet was high in saturated fat from animal fats, common margarines, and shortenings.

MAIN OUTCOME MEASURES

Death from all causes; association between changes in serum cholesterol and death; and coronary atherosclerosis and myocardial infarcts detected at autopsy.

RESULTS

The intervention group had significant reduction in serum cholesterol compared with controls (mean change from baseline -13.8%v-1.0%; P<0.001). Kaplan Meier graphs showed no mortality benefit for the intervention group in the full randomized cohort or for any prespecified subgroup. There was a 22% higher risk of death for each 30 mg/dL (0.78 mmol/L) reduction in serum cholesterol in covariate adjusted Cox regression models (hazard ratio 1.22, 95% confidence interval 1.14 to 1.32; P<0.001). There was no evidence of benefit in the intervention group for coronary atherosclerosis or myocardial infarcts. Systematic review identified five randomized controlled trials for inclusion (n=10,808). In meta-analyses, these cholesterol lowering interventions showed no evidence of benefit on mortality from coronary heart disease (1.13, 0.83 to 1.54) or all cause mortality (1.07, 0.90 to 1.27).

CONCLUSIONS

Available evidence from randomized controlled trials shows that replacement of saturated fat in the diet with linoleic acid effectively lowers serum cholesterol but does not support the hypothesis that this translates to a lower risk of death from coronary heart disease or all causes. Findings from the Minnesota Coronary Experiment add to growing evidence that incomplete publication has contributed to overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.

Effect of modified dairy fat on fasting and postprandial haemostatic variables in healthy young men

It has been suggested that milk fat, due to its content of saturated fatty acids, may have a thrombogenic effect. In the present study the fatty acid profile of milk fat was modified by changing the feeding regimens of cows and the effect on haemostatic variables of a diet containing the modified milk fat (M) was compared with that of a diet containing milk fat of typical Danish composition (D). In the modified fat 16% of the saturated fatty acid (C12–C16) content was replaced mainly by oleic acid. Eighteen subjects were fed on two strictly controlled isoenergetic diets containing 40% energy from total fat (30% energy from the test fats) for periods of 4 weeks in a study with a crossover design. Fasting samples were taken in the last week of each study period. Postprandial samples were taken on day 21, 3 h after lunch (n18), and on the last day of the study 2, 4, 6 and 8 h after a fat load containing 1·2 g of one of the milk fats/kg body weight (n8). After 4 weeks' dietary intervention fasting plasma factor VII coagulant (FVIIc) activity, tissue-type plasminogen activator (t-PA) activity, plasminogen activator inhibitor (PAI-1) antigen and β-thromboglobulin did not differ between diets M and D. Postprandially FVIIc and t-PA activities increased (P< 0·001) and PAI-1 antigen and PAI-1 activity decreased (P< 0·001) as compared with fasting values, regardless of diet. After the fat load, the postprandial increase in FVIIc was marginally lower after diet M than diet D (diet effect,P< 0·05). In conclusion, the modified milk fat obtained by the applied feeding strategy had virtually the same effects on haemostatic variables as conventional milk fat.

Difference in dietary intake between women with polycystic ovary syndrome and healthy controls

OBJECTIVE

To test the hypothesis that the dietary intake and dietary composition of women with polycystic ovary syndrome (PCOS) is associated with indices of glycemic status. We hypothesized that women with PCOS would consume a diet higher in total energy, fat, and specific foods with a high glycemic index than would healthy, control-group women and that dietary composition would be associated with indices of insulin resistance and secretion among women with PCOS.

DESIGN

Cohort study.

SETTING

Research center on a university campus.

PATIENT(S)

Thirty women with PCOS and 27 healthy, age-, race-, and body mass index (BMI)-matched control women.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Nutrient intake data were collected from a food questionnaire and a 4-day food record. Fasting sera were analyzed for concentrations of insulin and glucose; estimates of insulin resistance were calculated.

RESULT(S)

Consumption of total energy, macronutrients, micronutrients, and high glycemic index foods was similar between the groups. However, the PCOS group consumed significantly more white bread (7.9 +/- 4.4 vs. 5.5 +/- 2.9 servings over 4 days) and tended to consume more fried potatoes than did the control group (1.0 +/- 1.5 vs. 0.4 +/- 0.7 servings over 4 days). The PCOS group had a significantly greater fasting insulin concentration (22.5 +/- 14.9 vs. 15.1 +/- 8.3 muIU/mL) and a significantly lower glucose-to-insulin ratio (4.7 +/- 2.1 vs. 7.6 +/- 5.2) than the control group. Within the PCOS group, HOMA-IR and HOMA-%beta-cell function were significantly associated with BMI. The HOMA-IR, HOMA-%beta-cell, fasting insulin, and glucose-to-insulin ratio were not positively associated with measures of diet composition.

CONCLUSION(S)

Compared with matched control women, women with PCOS exhibited a dietary pattern that was marked by consumption of a greater amount of specific foods with a high glycemic index; however, diet composition was not associated with the greater fasting insulin concentration or with lower glucose-to-insulin ratio that was observed in the PCOS group.

The elimination of trans fats from spreads: how science helped to turn an industry around

Mensink and Katan showed in 1990 that trans fats reduce high- and increase low-density lipoprotein cholesterol. Unilever aided this study because the company considered knowledge on trans fats incomplete in spite of their long history of safe use. The decision in 1994 to remove trans fats from Unilever's retail spreads was triggered by media events, but it was built on a solid understanding of the nutritional and technological aspects of trans fats. Over the next 14 years, manufacturers worldwide followed suit. This experience illustrates that food companies need to know about the health effects of their products and how to apply that knowledge.

Ácidos graxos trans: implicações nutricionais e fontes na dieta

Este artigo revisa as principais fontes de ácidos graxos trans na dieta e as implicações nutricionais da ingestão elevada destes isômeros. São apresentados resumidamente os métodos analíticos utilizados na identificação e quantificação dos ácidos graxos trans, sendo abordados as suas vantagens e desvantagens. Os alimentos que empregam gordura parcialmente hidrogenada na sua produção, são fontes importantes de isômeros trans na dieta da maior parte da população em países industrializados. Este estudo compara os níveis de ácidos graxos trans em gorduras hidrogenadas, margarinas e batatas frita, analisados em diversos países, incluindo o Brasil. Esta avaliação indica a presença de níveis elevados de isômeros trans em alimentos produzidos no Brasil.

Serum cholesterol predictive equations with special emphasis on trans and saturated fatty acids. an analysis from designed controlled studies

The effects of dietary trans fatty acids on serum total and low density lipoprotein (LDL) cholesterol have been evaluated by incorporating trans fatty acids into predictive equations and comparing their effects with the effects of the individual saturated fatty acids 12:0, 14:0, and 16:0. Trans fatty acids from partially hydrogenated soybean oil (TRANS V) and fish oil (TRANS F) were included in previously published equations by constrained regression analysis, allowing slight adjustments of existing coefficients. Prior knowledge about the signs and ordering of the regression coefficients was explicitly incorporated into the regression modeling by adding lower and upper bounds to the coefficients. The amounts of oleic acid (18:1) and polyunsaturated fatty acids (18:2, 18:3) were not sufficiently varied in the studies, and the respective regression coefficients were therefore set equal to those found by Yu et al. [Yu, S., Derr, J., Etherton, T.D., and Kris-Etherton, P.M. (1995) Plasma Cholesterol-Predictive Equations Demonstrate That Stearic Acid Is Neutral and Monounsaturated Fatty Acids Are Hypocholesterolemic, Am. J. Clin. Nutr. 61, 1129-1139]. Stearic acid (18:0), considered to be neutral, was not included in the equations. The regression analyses were based on results from four controlled dietary studies with a total of 95 participants and including 10 diets differing in fatty acid composition and with 30-38% of energy (E%) as fat. The analyses resulted in the following equations, where the change in cholesterol is expressed in mmol/L and the change in intake of fatty acids is expressed in E%: delta Total cholesterol = 0.01 delta(12:0) + 0.12 delta(14:0) + 0.057 delta(16:0) + 0.039 delta(TRANS F) + 0.031 delta(TRANS V) - 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3) and deltaLDL cholesterol = 0.01 delta(12:0) + 0.071 delta(14:0) + 0.047 delta(16:0) + 0.043 delta(TRANS F) + 0.025 delta(TRANS V) - 0.0044 delta(18:1) - 0.017 delta(18:2, 18:3). The regression analyses confirm previous findings that 14:0 is the most hypercholesterolemic fatty acid and indicate that trans fatty acids are less hypercholesterolemic than the saturated fatty acids 14:0 and 16:0. TRANS F may be slightly more hypercholesterolemic than TRANS V or there may be other hypercholesterolemic fatty acids in partially hydrogenated fish oil than those included in the equations. The test set used for validation consisted of 22 data points from seven recently published dietary studies. The equation for total cholesterol showed good prediction ability with a correlation coefficient of 0.981 between observed and predicted values. The equation has been used by the Norwegian food industry in reformulating margarines into more healthful products with reduced content of cholesterol-raising fatty acids.

Trans fatty acids and plasma lipoproteins

Perceptions of the health effects of trans fatty acids, particularly in the form of margarine, have undergone several changes during the past 10 years. What was once heralded as the healthy alternative to butter now assumes the role of coconspirator. A new study finds that consumption of trans fatty acids, such as those found in stick margarine and shortening, have negative effects on lipoprotein profiles that are comparable to those of saturated fatty acids. In the prevention and treatment of cardiovascular diseases, therefore, it is recommended that consumers reduce intakes of both saturated and trans fatty acids.

A high-trans fatty acid diet and insulin sensitivity in young healthy women

Epidemiological and experimental studies suggest that a diet rich in saturated fat affects insulin sensitivity. Monoenes and dienes that have an usaturated bond with the trans configuration (trans fatty acids) resemble saturated fatty acids with respect to structure, but no published data are available on the effect of trans fatty acids on insulin sensitivity. Therefore, the effects of diets high in trans fatty acids (TFA diet) and oleic acid (monounsaturated fat [MUFA] diet) on glucose and lipid metabolism were studied in 14 healthy women. Subjects consumed both experimental diets for 4 weeks according to a randomized crossover study design. Both experimental diet periods were preceded by consumption of a standardized baseline diet for 2 weeks. The diets provided 36.6% to 37.9% of energy (E%) as fat. In the TFA diet, there was 5.1 E% trans fatty acids, and in the MUFA diet, 5.2 E% oleic acid, substituted for saturated fatty acids in the baseline diet. A frequently sampled intravenous glucose tolerance test (FSIGT) was performed at the end of the experimental diet periods. Glucose effectiveness (S(G)) and the insulin sensitivity index (S(I)) did not differ after the two experimental diet periods. There was also no difference in the acute insulin response between the diets. The total cholesterol to high-density lipoprotein (HDL) cholesterol ratio and serum total triglyceride, HDL, and low-density lipoprotein (LDL) triglyceride and apolipoprotein B (apoB) concentrations were higher (P < .05) after the TFA diet. In conclusion, in young healthy women, the TFA diet resulted in a higher total/HDL cholesterol ratio and an elevation in triglyceride and apo B concentrations but had no effect on glucose and insulin metabolism compared with the MUFA diet.

Replacement of partially hydrogenated soybean oil by palm oil in margarine without unfavorable effects on serum lipoproteins

We have compared the effects of three different margarines, one based on palm oil (PALM-margarine), one based on partially hydrogenated soybean oil (TRANS-margarine) and one with a high content of polyunsaturated fatty acids (PUFA-margarine), on serum lipids in 27 young women. The main purpose of the study was to test if replacement of trans fatty acids in margarine by palmitic acid results in unfavorable effects on serum lipids. The sum of saturated fatty acids (12:0, 14:0, 16:0) was 36.3% of total fatty acids in the PALM-diet, the same as the sum of saturated (12:0, 14:0, 16:0) (12.5%) and trans (23.1%) fatty acids in the TRANS-diet. This sum was 20.7% in the PUFA-diet. The content of oleic acid was 37.9, 35.2, and 38.6%, respectively, in the three diets, whereas linoleic acid amounted to 16, 13.5, and 27.3%, respectively. Total fat provided 30-31% and the test margarines 26% of total energy in all three diets. The subjects consumed each of the diets for 17 d in a Latin-square crossover design. There were no significant differences in total cholesterol, low density lipoprotein (LDL)-cholesterol and apolipoprotein B (apoB) between the TRANS- and the PALM-diets. High density lipoprotein (HDL)-cholesterol and apoA-1 were significantly higher on the PALM-diet compared to the TRANS-diet whereas the ratio of LDL-cholesterol to HDL-cholesterol was lower, although not significantly (P = 0.077) on the PALM-diet. Total cholesterol, LDL-cholesterol, and apoB were significantly lower on the PUFA-diet compared to the two other diets. HDL-cholesterol was not different on the PALM- and the PUFA-diets but it was significantly lower on the TRANS-diet compared to the PUFA diet. Compared to the PUFA-diet the ratio of LDL- to HDL-cholesterol was higher on both the PALM- and the TRANS-diets whereas apoA-1 was not different. Triglycerides and lipoprotein (a) were not significantly different among the three diets. We concluded that nutritionally, palmitic acid from palm oil may be a reasonable alternative to trans fatty acids from partially hydrogenated soybean oil in margarine if the aim is to avoid trans fatty acids. A palm oil-based margarine is, however, less favorable than one based on a more polyunsaturated vegetable oil.

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

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

Trans fatty acids and cardiovascular risk

The major source of trans unsaturated fatty acid bearing fats (trans fats) is the partially hydrogenated fats present in margarines, salad and cooking oils. When ingested, trans fats are deposited in tissues but disappear when the nutritional stimulus is removed. They have no adverse effects on growth or reproduction in rats. Trans fats are hypercholesterolemic for rabbits and monkeys but no more atherogenic than their cis counterparts. In man, trans fats elevate cholesterol but the extent of elevation may depend on the level of dietary linoleic acid. In some, but not all, studies they elevate Lp(a); the difference may reflect the presence of specific trans isomers--an area that merits further studies. Tissue of subjects with coronary disease contain no more trans fatty acids than those of controls. Reviews of the literature by expert committees in the US and UK conclude that at current levels of intake dietary trans fats pose no health problems. However, more research is needed especially with regard to pregnancy, lactation, and neonatal health. Current concerns should not deflect our attention from the larger aspects of fat and health.

Effects of dietary fatty acid composition on plasma cholesterol

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

Impact of hydrogenated fat consumption on endogenous cholesterol synthesis and susceptibility of low-density lipoprotein to oxidation in moderately hypercholesterolemic individuals

The effects of replacing corn oil with corn oil margarine in stick form on endogenous cholesterol synthesis and susceptibility of low-density lipoprotein (LDL) to oxidation were assessed in 14 middle-aged and elderly men and women aged 63 +/- 12 years (mean +/- SD) with moderate hypercholesterolemia (mean LDL-cholesterol [LDL-C], 4.24 +/- 0.59 mmol/L at the time of recruitment). Subjects consumed each of two diets for 32-day periods, one enriched in corn oil, which contained 30% of energy as fat (7% saturated fatty acid [SFA], 9% monounsaturated fatty acid [MUFA] [0.4% 18:1n9 trans], and 11% polyunsaturated fatty acid [PUFA]) and 85 mg cholesterol/4.2 MJ, and one enriched in stick corn oil margarine, which contained 30% fat (8% SFA, 12% MUFA [4.2% 18:1n9trans], and 8% PUFA) and 77 mg cholesterol/4.2 MJ. Both diets were isocaloric and supplied by a metabolic research kitchen. Mean total cholesterol levels were lowest (P = .039) when subjects consumed the corn oil-enriched diet (5.01 +/- 0.51 mmol/L) as compared with the margarine-enriched diet (5.30 +/- 0.58 mmol/L). LDL-C levels were 3.24 +/- 0.51 and 3.50 +/- 0.54 mmol/L when subjects consumed corn oil-and margarine-enriched diets, respectively (P = .058). There were no significant differences in high-density lipoprotein cholesterol (HDL-C) or triglyceride concentrations between the two experimental periods. Consumption of the margarine-enriched diet versus the corn oil-enriched diet tended to result in lower cholesterol fractional synthetic rates ([C-FSRs] 0.0466 +/- 0.0175 and 0.0668 +/- 0.0298, respectively, P = .080) and cholesterol absolute synthetic rates ([C-ASRs] 1.1761 +/- 0.5375 and 1.6954 +/- 0.8685, respectively, P = .092); however, differences did not reach statistical significance. Consumption of the margarine-enriched diet versus the corn oil-enriched diet resulted in a significantly higher concentration of alpha-tocopherol in both plasma and LDL(P = .004 and P = .011, respectively). LDL particle size tended to be smaller after subjects consumed the margarine-enriched diet versus the corn oil-enriched diet (P = .103). Susceptibility of LDL to oxidation was similar after consumption of the corn oil- and margarine-enriched diets. These data suggest that an increased rate of endogenous cholesterol synthesis did not contribute to the higher plasma cholesterol concentrations during the period when subjects consumed the margarine-enriched diet. Therefore, the increase in cholesterol concentration resulting from margarine consumption was likely attributable, at least in part, to a decreased catabolic rate of cholesterol. Additionally, susceptibility of LDL to in vitro oxidation was not altered by consumption of hydrogenated fat.

Hyperlipidemic effects of trans fatty acids are accentuated by dietary cholesterol in gerbils

Trans isomers of dietary fatty acids, generated during the commercial hydrogenation of unsaturated fats, may contribute to coronary heart disease (CHD) in humans by interfering with lipid metabolism. To examine this possibility in a fat-sensitive model, the Mongolian gerbil (Meriones unguiculatus) was used to compare the cholesterolemic and triglyceridemic potential of modest increments of trans fatty acids from partially hydrogenated soybean oil with other saturated fatty acids in the presence and absence of dietary cholesterol. Age-, dose-, and time-dependent effects were examined in weanling, 6-month-old, and 1-year-old gerbils. Although lipoprotein metabolism in weanling gerbils was initially refractory to trans fat, even as perturbations by saturated fatty acids were demonstrable, these gerbils eventually (after 16 weeks) developed a trans-induced hypercholesterolemia that was intermediate between the response to 16:0 and 12:0 + 14:0. The hepatic and plasma 18:1/18:2 cholesteryl ester (CE) ratio was depressed by trans in a manner similar to saturated fatty acids. The 6-month-old gerbils readily developed hypertriglyceridemia but not hypercholesterolemia, again revealing a decrease in the plasma 18:1/18:2 CE ratio. The 1-year-old gerbils revealed a dose-related (0, 5, 10%en as trans) elevation in total cholesterol (TC), and especially triglycerides (TG), that was accentuated by 0.04% dietary cholesterol. Increases in plasma lipids were again accompanied by a significant decrease in the mass of hepatic esterified cholesterol, particularly 18:1-cholesteryl esters. Thus, dietary trans-fatty acids induce age-, time-, and dose-dependent modulations in gerbil plasma lipids associated with decreased 18:1 cholesteryl esters. Further investigation with gerbils may reveal mechanisms by which trans fat consumption disturbs lipoprotein metabolism.

Trans fatty acids: implications for health, analytical methods, incidence in edible fats and intake (a review)

Trans fatty acids (TFA) are supposed to be related to a variety of physiological effects. Numerous studies in this field are gathered and compared, which mainly deal with the influences on lipoprotein levels in plasma and their effects with regard to coronary heart diseases. Furthermore, the analytical accessibility of trans fatty acids by different methods is presented. Thus, the most reliable method for an exact quantitation of trans fatty acids in edible fats is the combination of Ag-TLC with GC. The contents of TFA, in particular trans-octadecenoic acids, in bovine and human milk fat, in partially hydrogenated vegetable fats and oils as well as in processed food from different countries, determined in numerous studies, are summarized. Especially results on the isomeric distribution of positional isomers of trans-octadecenoic acid may be of future interest, since negative metabolic activities might only originate from certain isomers. Finally, intake rates of TFA in several countries are presented. It can be concluded that there still is need for further nutritional studies and that the discussion about TFA should not neglect the comparison with the saturated fatty acids C12, C14 and C16.

Trans fatty acids, blood lipids, and cardiovascular risk: where do we stand?

According to conventional wisdom, dietary substitution of vegetable fats for animal fats reduces the risk of cardiovascular heart disease (CHD). However, all forms of vegetable fat are not alike, and new research indicates that consumption of hydrogenated rather than unhydrogenated vegetable oils may negatively influence plasma lipids and risk of CHD.

Hydrogenation impairs the hypolipidemic effect of corn oil in humans. Hydrogenation, trans fatty acids, and plasma lipids

The effects of plasma lipoproteins and apolipoproteins of replacing corn oil with corn-oil margarine in stick form as two thirds of the fat in the National Cholesterol Education Program (NCEP) Step 2 diet were assessed in 14 middle-aged and elderly women and men (age range, 44-78 years) with moderate hypercholesterolemia (low density lipoprotein cholesterol [LDL-C] range, 133-219 mg/dl [3.45-5.67 mmol/l] at screening). During each 32-day study phase, subjects received all their food and drink from a metabolic kitchen. Subjects were first studied while being fed a diet approximating the composition of the current US diet (baseline), which contained 35% of calories as fat (13% saturated fatty acids [SFAs], 12% monounsaturated fatty acids [MUFAs; 0.8% 18:1n-9 trans], and 8% polyunsaturated fatty acids [PUFAs]) and 128 mg cholesterol/1,000 kcal. This baseline phase was followed by a corn oil-enriched diet containing 30% fat (6% SFA, 11% MUFA [0.4% 18:1n-9 trans], and 10% PUFA) and 83 mg cholesterol/1,000 kcal, and then a corn-oil margarine-enriched diet containing 30% fat (8% SFA, 12% MUFA [4.2% 18:1n-9 trans], and 8% PUFA) and 77 mg cholesterol/1,000 kcal. All diets were isocaloric. Mean fasting LDL-C and apolipoprotein (apo) B levels were 153 mg/dl (3.96 mmol/l) and 101 mg/dl on the baseline diet, 17% and 20% lower (both p < 0.001) on the corn oil-enriched diet, and 10% and 10% lower (both p < 0.01) on the margarine-enriched diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Trans monounsaturated fatty acids in nutrition and their impact on serum lipoprotein levels in man

Trans-C18:1 in the diet originate predominantly from partially hydrogenated oils, with beef, mutton and dairy products being an additional source. These fatty acids are absorbed and incorporated into lipids. Their estimated consumption is about 5-7% of total fatty acids, although reliable data are lacking. In addition, large variations between individuals exist. There is no evidence that trans fatty acids accumulate in human tissues. Elaidic acid and its positional isomers do, however, raise LDL cholesterol and apoprotein B and Lp(a) and probably depress HDL cholesterol and apoprotein A-I, compared with the cis isomer, oleic acid. In view of these adverse effects, patients at high risk for atherosclerosis, in addition to reducing their intake of saturated fatty acids and of cholesterol might also do well to avoid excessive intakes of trans fatty acids. Still, trans fatty acids form only a minor component of the diets of most patients and therefore even marked relative reductions in intake will probably have less of an impact on LDL cholesterol than a sizeable reduction in saturated fatty acids and cholesterol will produce.

Effect of dietary trans fatty acids on high-density and low-density lipoprotein cholesterol levels in healthy subjects

BACKGROUND

Fatty acids that contain a trans double bond are consumed in large amounts as hydrogenated oils, but their effects on serum lipoprotein levels are unknown.

METHODS

We placed 34 women (mean age, 26 years) and 25 men (mean age, 25 years) on three mixed natural diets of identical nutrient composition, except that 10 percent of the daily energy intake was provided as oleic acid (which contains one cis double bond), trans isomers of oleic acid, or saturated fatty acids. The three diets were consumed for three weeks each, in random order.

RESULTS

On the oleic acid diet, the mean (+/- SD) serum values for the entire group for total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol were 4.46 +/- 0.66. 2.67 +/- 0.54, and 1.42 +/- 0.32 mmol per liter (172 +/- 26, 103 +/- 21, and 55 +/- 12 mg per deciliter), respectively. On the trans-fatty-acid diet, the subjects' mean HDL cholesterol level was 0.17 mmol per liter (7 mg per deciliter) lower than the mean value on the diet high in oleic acid (P less than 0.0001; 95 percent confidence interval, 0.13 to 0.20 mmol per liter). The HDL cholesterol level on the saturated-fat diet was the same as on the oleic acid diet. The LDL cholesterol level was 0.37 mmol per liter (14 mg per deciliter) higher on the trans-fatty-acid diet than on the oleic acid diet (P less than 0.0001; 95 percent confidence interval, 0.28 to 0.45 mmol per liter) and 0.47 mmol per liter (18 mg per deciliter) higher on the saturated-fat diet (P less than 0.001; 95 percent confidence interval, 0.39 to 0.55 mmol per liter) than on the oleic acid diet. The effects on lipoprotein levels did not differ between women and men.

CONCLUSIONS

The effect of trans fatty acids on the serum lipoprotein profile is at least as unfavorable as that of the cholesterol-raising saturated fatty acids, because they not only raise LDL cholesterol levels but also lower HDL cholesterol levels.

Diet and serum lipids: controlled studies in the United States

The influence of dietary fat on serum lipids is well established. The general principles of a fat-modified diet--calorie control and the amount and composition of dietary fat--are demonstrated in studies in which nutrient composition was systematically altered. Weight loss, even when caloric deficit involves no other changes in nutrients, reduces serum lipids. With isocaloric diets, the fatty acid composition rather than the amount of fat influences the serum cholesterol concentration. Saturated fatty acids are twice as effective in raising serum cholesterol levels as polyunsaturated fatty acids are in reducing them. The amount of cholesterol in the diet alters the amount in the serum by approximately 5 mg/dl for every 100 mg of change in diets with less than 300 mg/1000 kcal. Cholesterol in excess of this amount has no additional effect. With no dietary cholesterol, serum lipids are unaffected by the fat composition. In the presence of dietary cholesterol, serum lipids are affected by saturated and polyunsaturated fatty acids through an interaction with cholesterol. Polyunsaturates counteract the influence of both saturated fatty acids and cholesterol. The more cholesterol there is in the diet, the more polyunsaturated fatty acids are required to counteract its effect. Both the fatty acid composition of the lipoproteins and lipid metabolism are affected by the fat and cholesterol composition of the diet.

Incorporation of deuterium-labeled cis- and trans-9-octadecenoic acids in humans: plasma, erythrocyte, and platelet phospholipids

The objective of this study was to follow the uptake and distribution of oleic and elaidic acids into human erythrocytes, platelets, and plasma phospholipids. The use of dual and triple labeling methodology permitted a precise comparison of elaidic and oleic acid utilization. Elaidic acid (EI) was selectively concentrated in all the plasma phospholipids except for lysophosphatidylcholine. Three times more elaidic than oleic acid (OI) accumulated in the 1-acyl position of phosphatidylcholine, as determined by hydrolysis with phospholipase A2. Rapid incorporation and removal of elaidate were observed for all samples. These results support the concept that enzymes responsible for acylation of phospholipids are sensitive to double bond configuration and the physical properties of the fatty acid moieties. Labeled fatty acid levels in red cell and platelet phospholipids were much lower than for plasma phospholipids, indicating a relatively slow rate for the in vivo incorporation of fatty acids into blood cell membrane phospholipids. No isotope effect was found when oleic acid labeled with deuterium on the double bond was used.

Metabolism of linoleate versus linoelaidate in the laying hen

The metabolic fate in the laying hen of linolaidic acid, the trans,trans-geometric isomer of linoleic acid, was compared to that of the naturally occurring cis,cis linoleate. In two experiments, mixtures of radioisotope-labeled linoleate and linoelaidate were orally administered to a set of three laying hens. A third mixture consisting of linoleate-3H and linoleate-14C was fed to three hens to measure biological isotope effects. Isotopic ratios (3H/14C) of the neutral lipid and phospholipid fractions isolated from egg yolks and of the octadecadienoic acids from these fractions were compared to those of the administered mixtures. The 3H/14C ratios indicate that linoelaidic acid and linoleic acid are equally incorporated into egg yolk neutral lipids and phospholipids. Arachidonic acid was found exclusively in the phospholipid fraction and was radiolabeled with the isotope from the cis,cis octadecadienoate isomer only. Further detailed analysis of individual neutral lipid components indicated: (a) discrimination against the trans,trans isomer in cholesteryl esters and (b) no discrimination against either isomer in triacylglycerols.