Dietary palmitic and oleic acids exert similar effects on serum cholesterol and lipoprotein profiles in normocholesterolemic men and women

Composition, structure and absorption of milk lipids: a source of energy, fat-soluble nutrients and bioactive molecules

Milkfat is a remarkable source of energy, fat-soluble nutrients and bioactive lipids for mammals. The composition and content of lipids in milkfat vary widely among mammalian species. Milkfat is not only a source of bioactive lipid components, it also serves as an important delivery medium for nutrients, including the fat-soluble vitamins. Bioactive lipids in milk include triacylglycerides, diacylglycerides, saturated and polyunsaturated fatty acids, and phospholipids. Beneficial activities of milk lipids include anticancer, antimicrobial, anti-inflammatory, and immunosuppression properties. The major mammalian milk that is consumed by humans as a food commodity is that from bovine whose milkfat composition is distinct due to their diet and the presence of a rumen. As a result of these factors bovine milkfat is lower in polyunsaturated fatty acids and higher in saturated fatty acids than human milk, and the consequences of these differences are still being researched. The physical properties of bovine milkfat that result from its composition including its plasticity, make it a highly desirable commodity (butter) and food ingredient. Among the 12 major milk fatty acids, only three (lauric, myristic, and palmitic) have been associated with raising total cholesterol levels in plasma, but their individual effects are variable-both towards raising low-density lipoproteins and raising the level of beneficial high-density lipoproteins. The cholesterol-modifying response of individuals to consuming saturated fats is also variable, and therefore the composition, functions and biological properties of milkfat will need to be re-evaluated as the food marketplace moves increasingly towards more personalized diets.

The type of oil used for cooking is associated with the risk of nonfatal acute myocardial infarction in costa rica

Palm oil and soybean oil are the 2 most widely used cooking oils in the world. Palm oil is consumed mainly in developing countries, where morbidity and mortality due to cardiovascular disease (CVD) are on the rise. Although claims about adverse or protective effects of these oils are commonly made, there are no epidemiologic studies assessing the association between these oils and cardiovascular disease endpoints. We examined whether consumption of palm oil relative to soybean oil and other unsaturated oils (predominantly sunflower) is associated with myocardial infarction (MI) in Costa Rica. The cases (n = 2111) were survivors of a first acute MI and were matched to randomly selected population controls (n = 2111). Dietary intake was assessed with a validated semiquantitative FFQ. Adipose tissue profiles of essential fatty acids were assessed to validate cooking oil intake and found to be consistent with self-reported major oils used for cooking. The data were analyzed using conditional logistic regression. Palm oil users were more likely to have an MI than users of soybean oil [odds ratio (OR) = 1.33; 95% CI: 1.08-1.63] or other cooking oils (OR = 1.23; CI: 0.99-1.52), but they did not differ from users of soybean oil with a high trans-fatty acid content (OR = 1.14; CI: 0.84-1.56). These data suggest that as currently used in Costa Rica, and most likely in many other developing countries, the replacement of palm oil with a polyunsaturated nonhydrogenated vegetable oil would reduce the risk of MI.

Fatty acids and atherosclerotic risk

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

Saturated fats: what dietary intake?

Public health recommendations for the US population in 1977 were to reduce fat intake to as low as 30% of calories to lower the incidence of coronary artery disease. These recommendations resulted in a compositional shift in food materials throughout the agricultural industry, and the fractional content of fats was replaced principally with carbohydrates. Subsequently, high-carbohydrate diets were recognized as contributing to the lipoprotein pattern that characterizes atherogenic dyslipidemia and hypertriacylglycerolemia. The rising incidences of metabolic syndrome and obesity are becoming common themes in the literature. Current recommendations are to keep saturated fatty acid, trans fatty acid, and cholesterol intakes as low as possible while consuming a nutritionally adequate diet. In the face of such recommendations, the agricultural industry is shifting food composition toward lower proportions of all saturated fatty acids. To date, no lower safe limit of specific saturated fatty acid intakes has been identified. This review summarizes research findings and observations on the disparate functions of saturated fatty acids and seeks to bring a more quantitative balance to the debate on dietary saturated fat. Whether a finite quantity of specific dietary saturated fatty acids actually benefits health is not yet known. Because agricultural practices to reduce saturated fat will require a prolonged and concerted effort, and because the world is moving toward more individualized dietary recommendations, should the steps to decrease saturated fatty acids to as low as agriculturally possible not wait until evidence clearly indicates which amounts and types of saturated fatty acids are optimal?

Specific fatty acids and human colorectal cancer: an overview

BACKGROUND

Evidence suggests that dietary fats are associated with risk of colorectal cancer. The effect of fats depends not only on the quantity, but also on their composition in specific fatty acids. Moreover, fats are peroxidizable, and peroxidation products as well as antioxidants play a role in the pathogenic process of colorectal cancer.

METHODS

The published literature was reviewed for the relationship between dietary intake or concentration of specific fatty acids in adipose tissue, erythrocytes, plasma or feces in relation to colorectal cancer.

RESULTS

Increased concentrations of short-chain fatty acids (SCFAs) and eicosanopentaenoic acid (EPA) seem to protect against colorectal cancer. Increased concentrations of medium-chain fatty acids (MCFAs) and arachidonic acid (AA) might be associated with increased risk. Long-chain saturated fatty acids (LCSFAs) seem unrelated to colorectal cancer, while the associations between monounsaturated fatty acids (MUFAs), trans fatty acids, polyunsaturated fatty acids (PUFAs) such as linoleic acid (LA), alpha-linolenic acid (ALA), docosahexaenoic acid (DHA), omega-3/omega-6 ratio and colorectal cancer are unconvincing.

CONCLUSIONS

It is suggested that the substitution of food with high MCFAs and AA content by a SCFAs- and EPA-rich diet may contribute to reduced risk of colorectal cancer.

Replacing 40% of dietary animal fat with vegetable oil is associated with lower HDL cholesterol and higher cholesterol ester transfer protein in cynomolgus monkeys fed sufficient linoleic acid

This study was designed to evaluate whether replacing approximately 40 g/100 g dietary animal fat with vegetable oil would improve plasma lipids and lipoproteins when diets contained prudent levels of total saturated acid (SFA), monounsaturated acid (MUFA) and PUFA. Using a cross-over design, male Cynomolgus monkeys (n = 10) were fed purified diets containing a mixture of fats. For the diet based on animal fat (AF-diet), approximately 85 g/100 g of the total fat was derived from pork fat, and approximately 40 g/100 g of this was replaced with olive oil for the vegetable oil-based diet (VO-diet). Thus, the fat content of the VO diet comprised 50% pork fat and 35% olive oil. The remaining 15% of the total fat (for both diets) was safflower oil. Both diets provided approximately 30% of total energy (%en) from fat, <10%en SFA and approximately 6-7%en from PUFA. Monkeys were rotated through two 7-wk feeding periods, during which time plasma lipids and lipoproteins were evaluated. Compared with the AF diet, plasma total cholesterol (TC) concentrations tended to be lower ( approximately 10%) after monkeys consumed the VO diet (3.18 +/- 0.83 vs. 3.52 +/- 0.93 mmol/L, P = 0.099), and this was due entirely to a significant 12% reduction in HDL cholesterol (1.53 +/- 0.41 vs. 1.73 +/- 0.47, mmol/L, P = 0.0009). Although plasma lipoprotein compositional analyses revealed no significant differences in either lipoprotein composition or the estimated particle diameters, the measurement of cholesterol ester transfer protein (CETP) using (3)H-cholesterol ester-labeled HDL revealed that the lower HDL cholesterol (HDL-C) when monkeys consumed the VO diet was associated with a 31% increase in transfer (P = 0.04). However, despite the changes in HDL-C, the TC/HDL-C ratio did not differ between monkeys after the two diet treatments. Regression analyses of data from these monkeys revealed a significant correlation between the dietary 16:0/18:2 ratio and plasma HDL-C. These data suggest that within the context of currently recommended prudent diets, it may be possible to manipulate HDL-C beneficially. Whether a similar effect would occur in humans warrants investigation.

Cholesterolaemic effect of palmitic acid in relation to other dietary fatty acids

The effect of dietary intake of high palmitic acid levels in combination with other fatty acids in normal subjects was assessed. Palmitic acid (10% of energy) was fed in conjunction with decreasing levels of linoleic acid to determine if a threshold level of linoleic acid prevented palmitic acid from being hypercholesterolaemic. Healthy subjects received each of the diet treatments for 21 days, followed by washout periods of 7 days. In a second experiment, the effect of exchanging palmitic acid for trans fatty acids on plasma lipoprotein cholesterol levels and on rates for endogenous synthesis of cholesterol in normal subjects was investigated. Diet treatment lasted for 30 days. On day 30 of each diet treatment, a priming dose of deuterium was consumed, followed by a subsequent blood sample at 24 h. Blood cholesterol fractions were isolated and analysed by isotope ratio mass spectrometry to measure cholesterol fractional synthetic rates. In the first experiment, total plasma cholesterol levels increased as the percentage of linoleic acid decreased. The data indicated that high levels of palmitic acid were not hypercholesterolaemic if intake of linoleic acid was greater than 4.5% of energy. When the diet contained trans fatty acids plasma total and low-density lipoprotein-cholesterol increased and cholesterol synthesis increased with a decrease in high-density lipoprotein-cholesterol.

Effect of palm olein oil in a moderate-fat diet on plasma lipoprotein profile and aortic atherosclerosis in non-human primates

Several studies have reported on the effect of palm olein oil (PO; palmitic acid content approximately 38%) incorporation into the diet on blood cholesterol concentration. Information on the effect of PO on atherosclerosis is, however, lacking. In vervet monkeys (Cercopithecus aethiops), low-density lipoprotein cholesterol (LDL-C) concen-trations can be modulated by the type and amount of fat in the diet. The vervet is a proven model for both the type and composition of human atherosclerotic lesions. The aim of this study was to determine the effect of PO in a moderate-fat moderate-cholesterol diet (MFD) on plasma lipoproteins and the progression of atherosclerosis in a non-human primate model after 25.5 months of dietary exposure. Thirty adult male vervets, never exposed to a Western-type atherogenic diet, were stabilised on a MFD (28%E fat; 26 mg cholesterol/1000 kJ) with a polyunsaturated to saturated fatty acid (P/S) ratio of 0.4 for six weeks. Baseline LDL-C, high-density lipoprotein (HDL)-C and bodyweight were used to stratify the vervets into three comparable groups of 10 each. One group continued with the MFD in which 11.0%E was derived from lard (AF). In the other two groups, the AF was substituted isocalorically with either sunflower oil (SO) or PO. Plasma lipids were measured at 6-monthly intervals and atherosclerosis was assessed in the aorta and in five peripheral arteries after 25.5 months of dietary exposure. The frequency of atherosclerosis in peripheral arteries and aortas was low. PO, relative to SO and AF, significantly reduced the risk for developing early lesions in peripheral arteries (P = 0.0277 and P = 0.0038, respectively) and, relative to AF, in aortas (P = 0.0335). The cholesterolaemic effect of MFD-PO was not significantly different from MFD-SO and MFD-AF. However, at 24 months the plasma total cholesterol concentration with MFD-AF was significantly higher than with MFD-SO (P = 0.0256). It is confirmed that a MFD with PO is no different from AF or SO in its cholesterolaemic effect. The anti-atherogenic efficacy of a MFD with PO, relative to SO and AF, was demonstrated in a non-human primate model of atherogenesis.

Effect of dietary cholesterol, trans and saturated fatty acids on serum lipoproteins in non-human primates

Nine cynomolgus monkeys were rotated randomly through four dietary treatments with each treatment lasting 6 weeks. A wash-out period of 4 weeks was maintained between each dietary rotation. The animals were fed diets containing 32% energy fat derived from palm olein (POL), lauric-myristic-rich oil blend (LM), American Heart Association (AHA) rich oil blend and hydrogenated soybean oil blend (trans). Diets were fed with (phase 1) or without (phase 2) the addition of dietary cholesterol (0.1%). In phase 1, when animals were fed without dietary cholesterol, plasma total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) was significantly raised and high-density lipoprotein cholesterol (HDL-C) was significantly depressed by the trans diets relative to all other dietary treatments. The resulting LDL-C/HDL-C ratio was also significantly increased. The LM diet increased TC significantly relative to the AHA diet while LDL-C was significantly increased compared to both POL and AHA. Apolipoprotein (apo) B was not affected significantly by these dietary treatments. Apo A1 was significantly increased by POL relative to all other dietary treatments. The trans diet reduced apo A1 and the resulting apo B/A1 ratio was increased significantly by trans relative to all other dietary treatments. Addition of 0.1% dietary cholesterol to these diets almost doubled the plasma TC and LDL-C in all dietary treatments. However, HDL-C was only marginally higher with the addition of dietary cholesterol. The LM + C (cholesterol added) diet resulted in the highest TC and LDL-C that was significant compared to all other dietary treatments. Trans + C increased TC compared to POL + C and AHA + C diets while increases in the LDL-C did not attain significance. The addition of dietary cholesterol did not affect HDL-C between treatments whereas plasma triglycerides were significantly increased by the trans + C diet relative to all other treatments. Both the trans + C and LM + C diets increased apo B and decreased apo A1 relative to the POL + C and AHA + C diets. The resulting apo B/A1 ratio was similarly altered. These results affirm that the lauric + myristic acid combination, along with trans fatty acids, increased lipoprotein-associated coronary heart disease risk factors compared to either POL or AHA.

Assessment of risk associated with specific fatty acids and colorectal cancer among French-Canadians in Montreal: a case-control study

BACKGROUND

Discrepancies in findings on the association between dietary fats and colorectal cancer (CRC) persist, and it is hypothesized that fatty acids (FA) may modulate CRC risk because of their physiological functions.

METHODS

Between 1989 and 1993, a case-control study involving 402 cases and 668 population-based controls was conducted among French-Canadians. Dietary intake was assessed by a food frequency questionnaire.

RESULTS

Oleic acid was the major FA consumed by the study population. A significant inverse association was found among females between CRC and butyrate (OR = 0.57; 95% CI: 0.34-0.96; P = 0.006), alpha-linoleic acid (ALA) (OR = 0.78; 95% CI: 0.46-1.32; P = 0.016), and w-3 FA (OR = 0.84; 95% CI: 0.50-1.41; P = 0.028), comparing the upper to the lower quartiles of intake. An increased risk was associated with arachidonic acid (AA) (OR = 2.03; 95% CI: 1.16-3.54; P = 0.001) among males, and with the w6/w3 ratio (OR = 1.47; 95% CI: 0.86-2.50; P = 0.001) among females. Arachidonic acid was linked with up to fivefold increased risk (OR = 5.33; 95% CI: 2.04-13.95; P = 0.0004 for trend) among men with high vitamin C intake. Females with low carotenoids intake were at elevated risk associated with AA (OR = 4.07; 95% CI: 1.84-8.99; P = 0.003); eicosapentaenoic acid (OR = 3.50; 95% CI: 1.59-7.71; P = 0.015), and docosahexaenoic acid (OR = 5.77; 95% CI: 2.50-13.33; P = 0.002), comparing the upper with the lower quartiles of intake.

CONCLUSION

The results of this study suggest that independently of total energy intake, substituting AA by butyrate, ALA, or omega-3 FA may reduce CRC risk. The role of interactions between vitamin C, total carotenoids, and polyunsaturated FA requires further investigation.

Palm oil: a healthful and cost-effective dietary component

Palm oil is an excellent choice for food manufacturers because of its nutritional benefits and versatility. The oil is highly structured to contain predominantly oleic acid at the sn2-position in the major triacylglycerols to account for the beneficial effects described in numerous nutritional studies. Oil quality and nutritional benefits have been assured for the variety of foods that can be manufactured from the oil directly or from blends with other oils while remaining trans-free. The oxidative stability coupled with the cost-effectiveness is unparalleled among cholesterol-free oils, and these values can be extended to blends of polyunsaturated oils to provide long shelf-life. Presently the supply of genetic-modification-free palm oil is assured at economic prices, since the oil palm is a perennial crop with unparalleled productivity. Numerous studies have confirmed the nutritional value of palm oil as a result of the high monounsaturation at the crucial 2-position of the oil's triacylglycerols, making the oil as healthful as olive oil. It is now recognized that the contribution of dietary fats to blood lipids and cholesterol modulation is a consequence of the digestion, absorption, and metabolism of the fats. Lipolytic hydrolysis of palm oil glycerides containing predominantly oleic acid at the 2 position and palmitic and stearic acids at the 1 and 3 positions allows for the ready absorption of the 2-monoacrylglycerols while the saturated free fatty acids remain poorly absorbed. Dietary palm oil in balanced diets generally reduced blood cholesterol, low-density lipoprotein (LDL) cholesterol, and triglycerides while raising the high-density lipoprotein (HDL) cholesterol. Improved lipoprotein(a) and apo-A1 levels were also demonstrated from palm oil diets; an important benefits also comes from the lowering of blood triglycerides (or reduced fat storage) as compared with those from polyunsaturated fat diets. Virgin palm oil also provides carotenes apart from tocotrienols and tocopherols that have been shown to be powerful antioxidants and potential mediators of cellular functions. These compounds can be antithrombotic, cause an increase of the prostacyclin/thromboxane ratio, reduce restenosis, and inhibit HMG-CoA-reductase (thus reducing) cholesterol biosynthesis). Red palm oil is a rich source of beta-carotene as well as of alpha-tocopherol and tocotrienols.

Dietary fat saturation affects apolipoprotein AII levels and HDL composition in postmenopausal women

Increased HDL-cholesterol levels have been associated with lower coronary heart disease (CHD) risk. However, HDL are heterogeneous lipoproteins, and particles enriched in apolipoprotein (Apo) AII have been associated with increased CHD risk. We examined the effect of dietary intervention on HDL composition in 14 postmenopausal women subjected to two consecutive diet periods, i.e., an oleic acid sunflower oil diet followed by a palmolein diet, each lasting 4 wk. The linoleic acid was kept at 4% total energy and the cholesterol intake at 400 mg/d. The palmolein diet increased serum total cholesterol (TC) (P < 0.001), phospholipids (P < 0.001), Apo AII (P < 0.001), HDL cholesterol (P < 0.05), HDL lipids (P < 0.05), HDL proteins (P < 0.01) and the HDL total mass (P < 0.05). The HDL cholesterol/Apo AI ratio was increased 22.0% (P < 0.05), whereas the HDL cholesterol/Apo AII and the Apo AI/Apo AII ratios were decreased 19.4% (P < 0.01) and 30.4%, (P < 0.001), respectively. When the effects of the dietary intervention were examined according to the cholesterolemia status (< or >6.2 mmol/L), the most significant changes (P < 0.001) were related to Apo AII levels. Moreover, a significant dietary oil by cholesterol level interaction was found for Apo AII and the HDL cholesterol/Apo AII ratio. In summary, a palmolein diet increased TC and HDL cholesterol compared with oleic acid sunflower oil diet; however, the increase in Apo AII but not in Apo AI suggests the impairment of reverse cholesterol transport and potentially an increase in CHD risk. This effect was more marked in women with serum TC > 6.2 mmol/L.

Palmitic and stearic acids similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

This study was designed to evaluate whether the exchange of specific saturated fatty acids [SFA; palmitic acid (16:0) for stearic acid (18:0)] would differentially affect plasma lipids and lipoproteins, when diets contained the currently recommended levels of total SFA, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA). Ten male cynomolgus monkeys were fed one of two purified diets (using a cross-over design) enriched either in 16:0 (palmitic acid diet) or 18:0 (stearic acid diet). Both diets provided 30% of energy as fat (SFA/monounsaturated fatty acid/PUFA: 1/1/1). The palmitic acid and stearic acid diets were based on palm oil or cocoa butter (59% and 50% of the total fat, respectively). By adding different amounts of sunflower, safflower and olive oils, an effective exchange of 16:0 for 18:0 of approximately 5% of energy was achieved with all other fatty acids being held constant. Monkeys were rotated through two 10-wk feeding periods, during which time plasma lipids and in vivo lipoprotein metabolism (following the simultaneous injection of (131)I-LDL and (125)I- HDL were evaluated). Plasma triacyglycerol (0.40 +/- 0.03 vs. 0.37 +/- 0.03 mmol/L), plasma total cholesterol (3.59 +/- 0.18 vs. 3.39 +/- 0.23 mmol/L), HDL cholesterol (1.60 +/- 0.16 vs 1.53 +/- 0.16 mmol/L) and non-HDL cholesterol (2.02 +/- 0.26 vs. 1.86 +/- 0.23 mmol/L) concentrations did not differ when monkeys consumed the palmitic acid and stearic acid diets, respectively. Plasma lipoprotein compositional analyses revealed a higher cholesteryl ester content in the VLDL fraction isolated after consumption of the stearic acid diet (P < 0.10), as well as a larger VLDL particle diameter (16.3 +/- 1.7 nm vs. 13.8 +/- 3.6 nm; P < 0.05). Kinetic analyses revealed no significant differences in LDL or HDL transport parameters. These data suggest that when incorporated into diets following current guidelines, containing adequate PUFA, an exchange of 16:0 for 18:0, representing approximately 11 g/(d.10.46 mJ) [ approximately 11 g/(d.2500 kcal)] does not affect the plasma lipid profile and has minor effects on lipoprotein composition. Whether a similar effect would occur in humans under comparable dietary conditions remains to be established.

Pork fat and chicken fat similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

The effects on plasma lipoprotein metabolism of replacing pork fat (PF) with chicken fat (CF) (formulated as part of currently recommended prudent diets) was evaluated in 10 male cynomolgus monkeys. Monkeys were rotated through three dietary periods, (each of 10-wk duration), during which total cholesterol (TC), triacylglycerol (TG) and HDL-cholesterol (HDL-C) were measured (7, 8 and 9 wk) and in vivo lipoprotein metabolism evaluated (after 9 wk). Initially, all monkeys were fed a high-fat, high-cholesterol reference diet [38% of energy (en) from fat, 18%en saturated fatty acids (SFA), 10%en monounsaturated fatty acids (MUFA), 10%en polyunsaturated fatty acids (PUFA), 0.045 mg cholesterol/kJ diet]. Subsequently, monkeys were rotated through two test diets (30%en fat, SFA/MUFA/PUFA 1:1:1, 0.004-0.005 mg cholesterol/kJ diet), in which 80% of the fat was either PF or CF, with the remaining 20% derived from high-linoleic safflower oil. There was no significant difference between the two test diets for TG, TC, nonHDL-C, HDL-C or the ratio of TC/HDL-C. Lipoprotein composition, LDL apolipoprotein B pool size, fractional catabolic rate and transport rate were also not significantly different when monkeys consumed the two test diets. These data suggest that when incorporated into diets following current guidelines and containing adequate PUFA ( approximately 7-9%en), PF and CF similarly affect plasma lipids.

The effect of palmitic acid on lipoprotein cholesterol levels and endogenous cholesterol synthesis in hyperlipidemic subjects

The present study assesses the effect of high vs. low palmitic acid intakes on plasma lipoprotein cholesterol levels and on rates for endogenous synthesis of cholesterol in healthy and hyperlipidemic subjects. Four diets were formulated to provide combinations of 16:0 at two levels of 18:2n-6. Subjects received each diet treatment for 21 d, followed by washout periods of 21 d. On day 21 of each diet treatment, a fasting blood sample was drawn for lipoprotein determination and to provide a measure of the background level of deuterium. A priming dose of deuterium was consumed and a second blood sample obtained 24 h after the first sample. Isotope ratio mass spectrometry was used to determine the incorporation of deuterium into the newly synthesized cholesterol molecule, and fractional synthetic rates were calculated. Serum total cholesterol and low density lipoprotein-cholesterol was not significantly affected by the high level of 16:0 when diets also contained a high level of 18:2n-6. There was no effect of dietary 16:0 on high density liproprotein-cholesterol at either the high or low levels of intake. The results indicate that 16:0 has no effect on serum lipoprotein profiles in the presence of recommended intakes for 18:2n-6.

Use of hierarchical models for meta-analysis: experience in the metabolic ward studies of diet and blood cholesterol

Overviews that combine single effect estimates from published studies generally use a summary statistic approach where the effect of interest is first estimated within each study and then averaged across studies in an appropriately weighted manner. Combining multiple regression coefficients from publications is more problematic, particularly when there are differences in study design and inconsistent reporting of effect sizes and standard errors. This paper describes the use of a hierarchical model in such circumstances. Its use is illustrated in a meta-analysis of the metabolic ward studies that have investigated the effect of changes in intake of various dietary lipids on blood cholesterol. These studies all reported average blood cholesterol for groups of individuals who were studied on one or more diets. Thirty-one studies had randomized cross-over designs, 12 had matched parallel group designs, 12 had non-randomized Latin square designs and 16 had other uncontrolled designs. The hierarchical model allowed the different types of comparison (within-group between-diet, between matched group) that were made in the various studies to each contribute to the overall estimates in an appropriately weighted manner by distinguishing between-study variation, within-study between-matched-group variation and within-group between-diet variation. The hierarchical models do not require consistent specification of effect sizes and standard errors and hence have particular utility in combining results from published studies where the relationships between a dependent variable and two or more predictors have been investigated using heterogeneous methods of analysis.

The role of linoleic acid in endothelial cell gene expression. Relationship to atherosclerosis

There is evidence that linoleic acid plays a critical role in gene expression and vascular function as it relates to the pathogenesis of atherosclerosis. The lipid environment, particularly linoleic acid and its derivatives, of the vascular endothelium may profoundly influence the inflammatory response mediated by cytokines. Modulations in the level of activity of a select set of endothelial transcription factors appear to provide a mechanism for linking lipid/cytokine-mediated vessel wall dysfunction, including endothelial cell activation, altered proteoglycan metabolism, and endothelial barrier dysfunction, with the onset of atherosclerotic lesion formation. The activity of endothelial transcription factors is in part regulated by the balance of cellular oxidative stress and antioxidant status. Our data suggest that linoleic acid can activate the vascular endothelium and may thus be an atherogenic fatty acid. Furthermore, nutrients/chemicals with antioxidant properties can protect endothelial cells against lipid-mediated cell injury, suggesting that oxidative stress is a critical component in linoleic acid-mediated gene expression. Our discoveries that linoleic acid can influence significantly the cytokine-mediated inflammatory response may open new fields in dietary intervention of atherosclerosis.

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.

Functional food science and the cardiovascular system

Cardiovascular disease has a multifactorial aetiology, as is illustrated by the existence of numerous risk indicators, many of which can be influenced by dietary means. It should be recalled, however, that only after a cause-and-effect relationship has been established between the disease and a given risk indicator (called a risk factor in that case), can modifying this factor be expected to affect disease morbidity and mortality. In this paper, effects of diet on cardiovascular risk are reviewed, with special emphasis on modification of the plasma lipoprotein profile and of hypertension. In addition, dietary influences on arterial thrombotic processes, immunological interactions, insulin resistance and hyperhomocysteinaemia are discussed. Dietary lipids are able to affect lipoprotein metabolism in a significant way, thereby modifying the risk of cardiovascular disease. However, more research is required concerning the possible interactions between the various dietary fatty acids, and between fatty acids and dietary cholesterol. In addition, more studies are needed with respect to the possible importance of the postprandial state. Although in the aetiology of hypertension the genetic component is definitely stronger than environmental factors, some benefit in terms of the development and coronary complications of atherosclerosis in hypertensive patients can be expected from fatty acids such as alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid. This particularly holds for those subjects where the hypertensive mechanism involves the formation of thromboxane A2 and/or alpha 1-adrenergic activities. However, large-scale trials are required to test this contention. Certain aspects of blood platelet function, blood coagulability, and fibrinolytic activity are associated with cardiovascular risk, but causality has been insufficiently proven. Nonetheless, well-designed intervention studies should be initiated to further evaluate such promising dietary components as the various n-3 and n-6 fatty acids and their combination, antioxidants, fibre, etc. for their effect on processes participating in arterial thrombus formation. Long-chain polyenes of the n-3 family and antioxidants can modify the activity of immunocompetent cells, but we are at an early stage of examining the role of immune function on the development of atherosclerotic plaques. Actually, there is little, if any, evidence that dietary modulation of immune system responses of cells participating in atherogenesis exerts beneficial effects. Although it seems feasible to modulate insulin sensitivity and subsequent cardiovascular risk factors by decreasing the total amount of dietary fat and increasing the proportion of polyunsaturated fatty acids, additional studies on the efficacy of specific fatty acids, dietary fibre, and low-energy diets, as well as on the mechanisms involved are required to understand the real function of these dietary components. Finally, dietary supplements containing folate and vitamins B6 and/or B12 should be tested for their potential to reduce cardiovascular risk by lowering the plasma level of homocysteine.

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.

Nonhypercholesterolemic effects of a palm oil diet in Chinese adults

The effects on serum lipids of palm oil (PA) used in Chinese diets were compared with those of soybean oil (SO), peanut oil (PE) and lard (LA) in normocholesterolemic subjects and with that of PE in hypercholesterolemic subjects. Normocholesterolemic subjects [120 men, 18-25 y, total cholesterol (TC) 2.8-5.0 mmol/L] were assigned to four groups to consume test diets for six consecutive weeks after a run-in period of 3 wk. About 30% of dietary energy was derived from fat, 75-80% of which came from test oils. In comparison with the entry level, the average serum TC and LDL cholesterol (LDL-C) were 6.7 and 13.1% lower, respectively, in the PA group and 22.8 and 30.7% higher, respectively, (P < 0.05) in the LA group. At the end of the test, serum TC, LDL-C and the ratio of TC/HDL cholesterol (HDL-C) in the PA group were significantly lower than those of the LA group. Hypercholesterolemic subjects (31 men, 20 women, 32-68 y, TC 5.5-7.0 mmol/L) were divided into two groups. For 6 wk, one group (15 men, 10 women) consumed the PA diet; another group (16 men, 9 women) consumed the PE diet. After a 3-wk interval, the two groups interchanged diets for another 6 wk. The test diets again contained about 30% energy from fat, 60-65% of which came from test oils. Compared with entry values, the PA diet caused significant reductions in serum TC, LDL-C and TC/HDL-C during the first 6 wk and also a significant reduction in TC/HDL-C during the second 6 wk. The PE diet had no significant influence on serum lipids in either experimental period.

Decreasing dietary lauric and myristic acids improves plasma lipids more favorably than decreasing dietary palmitic acid in rhesus monkeys fed AHA step 1 type diets

Current dietary recommendations advocate reductions in saturated fatty acids (SFA) and cholesterol (C) as a primary intervention for achieving a more desirable plasma lipid profile. To ascertain whether it is more efficacious to decrease dietary lauric and myristic acids (12:0 + 14:0) or dietary palmitic acid (16:0) in conjunction with a reduction in dietary C, 11 rhesus monkeys (8 males, 3 females) were initially fed a control diet rich in SFA + C for 14 wk [dietary fat approximately 38% of energy (%en), SFA 16%en and C at 180 mg/1000 kcal]. Plasma lipids were measured between the 9th and 13th wk, and LDL metabolism was assessed after 13 wk. Monkeys were then split into two groups and fed one of two American Heart Association (AHA) Step 1 diets (approximately 30%en fat, 10%en SFA, 75 mg cholesterol/1000 kcal) for an additional 14 wk, and plasma lipids and LDL metabolism were re-evaluated. Group 1 received a 16:0-rich diet in which most 12:0 + 14:0 were deleted (approximately 8.6%en from 16:0 and approximately 0.3%en from 12:0 + 14:0), whereas Group 2 received a diet rich in 12:0 + 14:0 from which 16:0 was selectively removed (2.6%en from 16:0 and approximately 6.3%en 12:0 + 14:0). In all three diets, oleic and linoleic acid were held relatively constant so that only SFA, the level of total fat and cholesterol were manipulated. Only the Step 1 diet that selectively removed 12:0 + 14:0 (the 16:0-rich diet) significantly reduced all lipid fractions, including total cholesterol (TC), HDL-C, LDL-C, apolipoprotein B (apoB) and the LDL pool size. Plasma triglyceride (TG) and the ratio of TC/HDL-C were not altered by either Step 1 diet. The smaller LDL pool size following the 16:0-rich diet in Group 1 was attributable to a significantly higher fractional catabolic rate (FCR) of LDL because the transport rate of LDL apoB was unaffected. Although the FCR was increased with the 12:0 + 14:0-rich diet, the LDL apoB pool was not affected because the transport rate of LDL tended to increase as well. The data suggest that a Step 1 diet that reduces total fat by decreasing 12:0 + 14:0 in conjunction with dietary C, improves plasma lipids more favorably than a similar diet that selectively removes 16:0 and C. Previous data would imply that the benefit resulted from removal of 12:0 + 14:0 per se, but the possibility is not eliminated that removal of C (independent of 12:0 + 14:0) muted the potential interaction between C and palmitic acid that tends to raise TC.

Trans (elaidic) fatty acids adversely affect the lipoprotein profile relative to specific saturated fatty acids in humans

Although dietary trans fatty acids can affect plasma lipoproteins negatively in humans, no direct comparison with specific saturated fatty acids has been reported, even though trans fatty acids were designed to replace saturates in foods and food processing. In this study, dietary trans 18:1 [elaidic acid at 5.5% energy (en)] was specifically exchanged for cis 18:1, 16:0 or 12:0 + 14:0 in 27 male and female subjects consuming moderate fat (31% en), low cholesterol (<225 mg/d) whole food diets during 4-wk diet periods in a crossover design. The trans-rich fat significantly elevated total cholesterol and LDL cholesterol relative to the 16:0-rich and 18:1-rich fats and uniquely depressed HDL cholesterol relative to all of the fats tested. Trans fatty acids also elevated lipoprotein (a) [Lp(a)] values relative to all dietary treatments. Furthermore, identical effects on lipoproteins were elicited by 16:0 and cis 18:1 in these subjects. The current results suggest that elaidic acid, one of the principal trans isomers produced during industrial hydrogenation of edible oils, adversely affects plasma lipoproteins. Thus, the negative effect of elaidic acid on the lipoprotein profile of humans appears to be unmatched by any other natural fatty acid(s).

Comparative lipoprotein metabolism of myristate, palmitate, and stearate in normolipidemic men

This project was designed to test the hypothesis that long-chain saturated fatty acids (myristate, palmitate, and stearate) are metabolized differently in human subjects, and that these differences may therefore account for the changes in plasma lipoprotein composition when these fatty acids are altered in the diet. Ethyl esters of each of the stable-isotope-labeled fatty acids (2H3- or 2H4-myristate, 13C16-palmitate, and 13C18-stearate) were fed to five nonhyperlipidemic men. The concentration of each labeled fatty acid was monitored for up to 72 hours as the fatty acids were assimilated into the lipid components (phospholipid [PL], triglyceride [TG], and cholesteryl ester [CE]) of the plasma lipoproteins (TG-rich lipoproteins [TRL], intermediate-density [IDL], low-density [LDL], and high-density lipoprotein [HDL]). Over 95% of the myristate was incorporated into TG, whereas 33% and 9% of the stearate and 18% and 7% of the palmitate were incorporated into PL and CE, respectively. The mean residence times (MRTs) for myristate in TG (8.6 to 9.9 hours) and PL (6.7 to 10.9 hours) in the individual lipoprotein subfractions were significantly shorter than for either palmitate (TG, 12.7 to 15.3 hours; PL, 19.6 to 21.3 hours) or stearate (TG, 10.7 to 15.5 hours; PL, 17.8 to 19.9 hours). The MRTs for stearate were shorter than for palmitate in PL. These data indicate that TG fatty acid in general, and myristate TG in particular, is the most rapidly cleared of the saturated fatty acids. There was a rapid transfer of labeled TG and PL between the lipoproteins. We were unable to detect any significant amount of stearate desaturation or elongation. In conclusion, these data demonstrate that myristate, palmitate, and stearate are metabolized in unique ways, and that it may therefore be inappropriate to continue to regard all "saturated fatty acids" as metabolically similar in clinical studies. Rather, it is important that we elucidate more clearly the specific metabolic pathway of each fatty acid to understand the mechanisms by which it alters plasma lipoprotein concentrations and composition and influences atherogenesis.

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.

Different effects of palmitic and stearic acid-enriched diets on serum lipids and lipoproteins and plasma cholesteryl ester transfer protein activity in healthy young women

The effects of palmitic and stearic acid-enriched diets on serum lipids, lipoproteins, apolipoproteins (apo) A-I and B, and plasma cholesteryl ester transfer protein (CETP) activity were examined in 12 healthy young women. Subjects followed the two experimental diets for 4 weeks according to a randomized crossover design. Both experimental diet periods were preceded by consumption of a baseline diet for 2 weeks. The diets provided 37% of total energy intake (E%) as fat, and differed only with respect to fatty acid composition. There was a substitution of 5E% of palmitic acid or stearic acid in the experimental diets for 5E% of monounsaturated fatty acids in the baseline diet. After the palmitic acid diet, serum total and high-density lipoprotein (HDL) cholesterol and apo A-I concentrations were higher (8%, P = .015, 9%, P = .040, and 11%,P = .011, respectively) and mean serum low-density lipoprotein (LDL) cholesterol concentration tended to be higher (8%, P = .077) as compared with values after the stearic acid diet. Plasma CETP activity increased in the palmitic acid diet as compared with the stearic acid diet (12%, P = .006). In conclusion, palmitic acid and stearic acid-enriched diets had different effects on serum lipids and lipoproteins and also on plasma CETP activity in young healthy women.

Plasma lipids are affected similarly by dietary lauric or palmitic acid in gerbils and monkeys

To compare the relative impact of dietary lauric acid (12:0) and palmitic acid (16:0) on plasma lipids, two fat-sensitive species, Mongolian gerbils and cebus monkeys, were fed cholesterol-free, purified diets enriched with either 12:0-rich or 16:0-rich fats, while all other fatty acids were held constant by selective blending of up to five natural fats or oils. The two gerbil diets (40 en% from fat) allowed for an 8 en% exchange between 12:0 and 16:0, and the monkey diets (31 en% from fat) allowed for 6 en% exchange between these two fatty acids. Eight gerbils received the diets for eight weeks, and 12 cebus monkeys were fed each diet in a cross-over design for up to 22 wk. Both diets resulted in similar plasma cholesterol, triglyceride, and high density lipoprotein cholesterol concentrations within each species. Additionally, separation of cebus lipoproteins by discontinuous density-gradient ultracentrifugation failed to show any dietary differences in concentration or composition of the three major lipoprotein classes (d < 1.019, 1.019-1.055, and 1.055-1.168 g/mL). Thus, in two species sensitive to manipulations in dietary fat while consuming cholesterol-free diets, 16:0 was not hypercholesterolemic relative to 12:0.

Effects of sex and ethnicity on responses to a low-fat diet: a study of African Americans and whites

The effects of sex and ethnicity on plasma lipoprotein changes that occur with low-fat diets were studied in 34 African American subjects (20 women, 14 men) and 29 white subjects (13 women, 16 men) aged 25-62 y with moderate hypercholesterolemia. A baseline diet containing 37% fat (15% saturated) was compared with four experimental diets containing 30% fat (10% saturated) with reciprocally varying contents of polyunsaturated and monounsaturated fatty acids. Diets were fed for 6 wk each, and all food and beverages provided and compliance were intensively monitored. Body weight and physical activity were held constant. Lowering of total and low-density-lipoprotein cholesterol were similar between women and men and between African Americans and whites. Small differences were observed between women and men in the extent of high-density lipoprotein lowering and triacylglycerol elevations. Additionally, African American subjects had slightly higher triacylglycerol elevations than did white subjects. Results suggest that men and women of varied ethnic backgrounds should respond similarly to cholesterol-lowering diets. Studies are required to develop strategies for achieving dietary changes that consider diverse eating patterns and cultural barriers to dietary adherence.

Effects of dietary cholesterol and fat saturation on plasma lipoproteins in an ethnically diverse population of healthy young men

The individual effects of dietary cholesterol and fat saturation on plasma lipoprotein concentrations were determined in an ethnically diverse population of normolipidemic young men (52 Caucasian, 32 non-Caucasian). The experimental diets contained approximately 200 or 600 mg/d of cholesterol, 36-38% of calories as fat, and high or low proportions of saturated and polyunsaturated fat (polyunsaturated/saturated fat ratio approximately 0.8 vs 0.3). At the lower cholesterol intake, the high saturated fat diet had only a modest effect on LDL cholesterol in Caucasians (+ 6 mg/dl-1) and none in non-Caucasians. 600 mg cholesterol with high saturated fat led to a substantial mean increase in LDL cholesterol, which was significantly greater in Caucasian than in non-Caucasian subjects (+ 31 mg/dl vs 16 mg/dl, P < 0.005). 600 mg cholesterol with increased polyunsaturated fat gave a mean LDL increase of 16 mg/dl, lower than found when the same high cholesterol intake was coupled with increased saturated fat. Variation in cholesterol rather than the proportions of saturated and polyunsaturated fat had the most influence on LDL-cholesterol levels. Among non-Caucasians it was the only significant factor.

Dietary saturated and trans fatty acids and lipoprotein metabolism

Earlier studies have shown that not all saturated fatty acids are equally hypercholesterolaemic: stearic acid (C18:0) and saturated fatty acids with less than 12 carbon atoms are thought not to raise serum cholesterol levels. This suggests that the cholesterol-raising effects of saturated fatty acids can be attributed to lauric acid (C12:0), myristic acid (C14:0) and palmitic acid (C16:0). These three saturated fatty acids also have different effects on serum total cholesterol levels. Results from recent controlled dietary experiments suggest that lauric acid raises serum total and low-density lipoprotein (LDL) cholesterol levels slightly less, and myristic acid more, as compared with palmitic acid. Myristic acid, however, also causes higher levels of high-density lipoprotein (HDL) cholesterol. Stearic acid has only a slight effect on serum LDL and HDL cholesterol levels as compared with oleic acid. Trans monounsaturated fatty acids, however, increase LDL and decrease HDL cholesterol levels. Precise effects on lipoproteins of short and medium chain triglycerides (C4:0-C10:0) have never been examined.

Impact of myristic acid versus palmitic acid on serum lipid and lipoprotein levels in healthy women and men

The cholesterol-raising effect of dietary saturated fatty acids is largely accounted for by lauric, myristic, and palmitic acids. Dairy fat is a major source of myristic acid, and palm oil is especially rich in palmitic acid. Myristic acid is suspected of being much more cholesterolemic than palmitic acid, but direct comparisons have been lacking. We therefore fed 36 women and 23 men three diets that differed from each other in palmitic, oleic, and myristic acid content by about 10% of total energy. We used palm oil, high-oleic acid sunflower oil, and a specially produced high-myristic acid fat to achieve these differences. Each diet was consumed for 3 weeks in random order. Mean serum cholesterol was 4.53 mmol/L on the high-oleic acid diet, 4.96 mmol/L on the palmitic acid diet, and 5.19 mmol/L on the myristic acid diet (P < .0001 for all comparisons). Myristic acid raised low-density lipoprotein (LDL) cholesterol by 0.11 mmol/L, high-density lipoprotein (HDL) cholesterol by 0.12 mmol/L, and apolipoprotein (apo) A-I by 7.2 mg/dL relative to palmitic acid; increases relative to oleic acid were 0.50 mmol/L for LDL cholesterol, 0.15 mmol/L for HDL cholesterol, 6.0 mg/dL for apoB, and 8.9 mg/dL for apoA-I (P < .01 for all comparisons). The HDL cholesterol and apoA-I levels on the palmitic and oleic acid diets were the same. None of the responses differed significantly between woman and men. Myristic acid and palmitic acid both caused high LDL cholesterol and apoB levels and low HDL to LDL ratios.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary palmitic acid raises plasma LDL cholesterol relative to oleic acid only at a high intake of cholesterol

Using a crossover design, the effects of exchanging up to 10% dietary energy (%en) between oleic (18:1) and palmitic acid (16:0) on plasma lipoprotein metabolism was investigated in 12 normocholesterolemic cebus monkeys, both in the absence and presence of dietary cholesterol (0.3%, w/w). In all the purified diets, which contained 33%en as fat blends, myristic acid (14:0) and linoleic acid (18:2) were held constant at 0.3%en and 3.7%en, respectively. Cholesterol-free diets containing either high 18:1 (19%en), roughly equivalent levels of 16:0 and 18:1 (12 and 15%en, respectively), or a high level of 16:0 (18%en), generated similar values for total plasma cholesterol (TC), HDL-C and LDL-C. Plasma triacylglycerol concentrations (TG) were significantly higher when monkeys were fed the 16: 0-rich diet than when fed the 18: 1-rich diet (75 +/- 6 vs. 52 +/- 8 mg/dl; P < 0.05). LDL and HDL kinetic parameters (assessed after simultaneous injection of homologous 131I-LDL and 125I-HDL) revealed no significant differences between the 18: 1-rich or 16: 0-rich diets. By contrast, with added dietary cholesterol (0.78 mg/kcal) the 16: 0-rich diet resulted in significantly higher TC (318 +/- 20 vs. 299 +/- 20 mg/dl; P < 0.05) and LDL-C (136 +/- 10 vs. 117 +/- 10 mg/dl; P < 0.05) in comparison to the 18: 1-rich diet. HDL-C was unaffected (159 +/- 8 vs. 156 +/- 5 mg/dl), but plasma TG concentrations also tended to be higher (70 +/- 8 vs. 60 +/- 6 mg/dl, P < 0.08). Kinetic studies revealed that the higher LDL-C concentration was associated with an elevated pool size of LDL apo B (40 +/- 2 vs. 34 +/- 2 mg/kg body weight; P < 0.005), the latter attributed to decreased FCR (1.06 +/- 0.07 vs. 1.27 +/- 0.12 pools/day; P < 0.04) with no effect on the transport rate of LDL apo B (41 +/- 2 vs. 42 +/- 3 mg/kg body weight per day). HDL kinetic parameters were comparable during the 16: 0 and 18: 1 dietary periods, but dietary cholesterol caused an increase in apo A-I pool size and transport rate without impacting FCR. In this study a palmitic acid-rich diet failed to alter plasma or LDL-C when compared to an oleic acid-rich diet, unless the diet also contained cholesterol. In the latter case, 16: 0 increased LDL-C, which reflected a decrease in the efficiency of LDL apo B removal.

Role of nutrition in the prevention and treatment of coronary heart disease in women

Coronary heart disease (CHD) is the major cause of death in women. Because the manifestation of CHD differs in women and men (men are more likely to have acute CHD and women are more likely to have chronic CHD), it is imperative to explore the unique aspects of CHD in women. In addition, there is a critical need to increase our understanding of the effect of CHD risk factor modification on coronary morbidity and mortality in women. Several major CHD risk factors in women, such as elevated blood lipids and lipoproteins, body weight, and, frequently, hypertension, are beneficially responsive to nutrition intervention. Approximately 27% of all women and 50% of women aged 55 to 74 years are candidates for dietary intervention. The fact that women respond positively to dietary intervention has been well established by researchers. Studies are needed to determine the efficacy of risk factor modification achieved by dietary and other hygienic approaches as well as by other more rigorous therapies (eg, drugs and surgery) on the primary and secondary prevention of CHD in women. Finally, it will be important to understand the effects of gender, menopausal status, and age on dietary responsiveness. We must gain a better understanding of these issues so that we may significantly reduce the incidence of CHD in women.