Feasibility of using an oleate-rich diet to reduce the susceptibility of low-density lipoprotein to oxidative modification in humans.

Oxidized low-density lipoprotein (LDL) is more atherogenic than native LDL. The initial step in the oxidation is the peroxidation of polyunsaturated fatty acids. Thus, decreasing the concentration of polyunsaturated fatty acids should reduce the susceptibility of LDL to oxidation. Therefore, we tested the possibility that diets enriched in oleate might result in LDL that is less susceptible to oxidative modification. LDL isolated from subjects consuming an oleate-enriched diet, compared with LDL from subjects on a linoleate-enriched diet, contained significantly more oleate (28.7% vs 11.5%) and less linoleate (31.9% vs 50.9%). Generation of conjugated dienes was significantly lower in the LDL from the oleate group. Most important, after incubation with endothelial cells, LDL from the oleate group underwent less degradation by macrophages. These studies demonstrate the feasibility of altering the diet in a way that will not raise LDL cholesterol concentrations and yet will decrease the susceptibility of LDL to oxidative modification.

Distribution among tissues of intravenously administered sucrose octaoleate.

The distribution of [14C]oleate label in rat tissues in the 6 hr after intravenous administration of sucrose octa[14C]oleate (7.5 mg; SuO8) was compared with that observed after administration of [14C]triolein. The [14C]oleate label, whether injected as triolein emulsion, or as chylomicrons obtained from donor animals, rapidly cleared from the serum; only 10% or less remained in the serum 15 min after injection. Labeled SuO8 disappeared less rapidly from the serum; about one-third of the dose was present after 15 min, and after 120 min 14% remained. In the liver, there was an initial greater accumulation of fatty acid label when an emulsion of either triolein or SuO8 was given rather than the chylomicrons. The octaester continued to accumulate in the liver throughout the 6 hr of study, and 78% of the initial dose was present at that time. By contrast, although one-third of the triolein, as of SuO8, was found in the liver shortly after injection, levels subsequently decreased; at 6 hr, 12% of the label remained associated with that organ. A small portion, up to 8% of the acid label, whether administered as chylomicrons or as a triolein emulsion, was found in the epididymal fat pads. Smaller amounts, usually 1% or less, of the [14C]oleate label were found in fat pads following the injection of labeled SuO8. In a separate study, the levels of acid label in the liver and spleen were monitored for 21 days following the intravenous administration of [14C]SuO8. There was an initial accumulation of approximately half of the injected lipid label in the liver and one-quarter in the spleen. By day 21, the level in the liver had decreased to one-third of that administered, while the level in spleen remained at one-quarter.

A changing role for dietary monounsaturated fatty acids.

Evidence is accumulating that diets low in saturated fatty acids and high in monounsaturated fatty acids are effective in controlling blood lipid levels; a likely consequence could be a beneficial effect on the risk of coronary heart disease. Although as yet limited in number, studies have shown monounsaturated fatty acids to be the equivalent of polyunsaturated fatty acids or low-fat diets in lowering blood low-density-lipoprotein cholesterol. The monounsaturated acids apparently have the added advantage of not causing a decrease in high-density-lipoprotein cholesterol or an increase in blood triglycerides, which can be a consequence of other dietary modifications. In the past, olive oil was the only fat rich in monounsaturated acids that was generally available in the United States. Recently, canola oil, a fat also rich in monounsaturates, has appeared in retail food outlets. Other potential sources are high oleic sunflower and safflower oils. Because the culinary and organoleptic properties of the monounsaturated-rich oils can be identical to those of currently used oils, they should be readily accepted by the consumer. Whether the preferred healthful diet is one low in fat or one high in monoenes or polyenes, the primary dietary recommendation remains--decrease the intake of saturated fat and cholesterol.

Customary diet, anthropometry, and dyslipoproteinemia in selected North American populations. The Lipid Research Clinics Program Prevalence Study.

The intake of nutrients, determined by 24 hr diet recall, and body measurements were obtained in 8250 free-living white study participants divided into 20 to 49 and 50 + age groups for males and female nonusers and users of gonadal hormones. They were classified into dyslipoproteinemia (DLP) phenotypes: hyperHDL, hypoHDL, IIA, hpypoLDL, IV, and normal. The dyslipoproteinemia DLP phenotypes, compared with the normal, had biologically meaningful differences in nutrient intake and indexes of obesity that were most marked for males aged 20 to 49 years as shown in the table (below). Those with the hyperHDL phenotype were thinner and ingested more energy and more alcohol and less carbohydrate as percent kilocalories (%kcal). Individuals classified as hypoHDL were fatter and tended to ingest less energy and less alcohol as %kcal. Persons with the type II phenotype were fatter and ingested less energy. Those with hypoLDL tended to be thinner and ingested more energy. Individuals with the type IV phenotype were fatter, ingested less energy and carbohydrate and more alcohol as %kcal. Similar trends were observed in female nonusers of hormones aged 20 to 49 and to a lesser extent in the 50 + age groups and in female users of hormones. Dietary protein, cholesterol, total fat, and polyunsaturated and saturated fatty acids had no consistent associations with DLP phenotype, and sucrose and starch had no association independent of total carbohydrate. This is the first evidence of an association of customary diet and DLP phenotypes in the free-living population. Equating energy intake with energy expenditure, persons with the high-risk phenotypes, IIA, IV, and hypoHDL, compared with the normal, had decreased energy expenditure and were fatter, whereas those with the low-risk phenotypes, hyperHDL and hypoLDL, had increased energy expenditure and were thinner.

The effect of a non-absorbable fat on the turnover of plasma cholesterol in the rat.

Rats were injected with [4-14C]-cholesterol and then fed diets that contained sucrose polyester (SPE) at levels of 0 and 8% of the diet. 14C was measured in neutral and acidic steroid fractions of the feces collected during days 35-39 post i.v. injection. Periodic blood samples were used to measure the specific activity of the plasma cholesterol. The plasma data were consistent with a two-pool model for the decay of the plasma specific activity. The slow component of the decay curve decreased more rapidly in animals that received SPE. The half-life corresponding to this component was approximately 20% shorter in the SPE-fed animals compared to the control group. The mass of cholesterol calculated for the first pool was similar for all groups of animals. The 14C found in the feces was consistent with the more rapid removal of cholesterol from the body in the SPE-fed animals. The mass of excreted steroid was equal to the calculated rate of cholesterol production in each group of animals.

Comparison of effects of dietary saturated, monounsaturated, and polyunsaturated fatty acids on plasma lipids and lipoproteins in man.

Twenty patients consumed a liquid diet in which the predominant fatty acids were either saturated (Sat), monounsaturated (Mono), or polyunsaturated (Poly). The fats in these three diets comprised 40% of total calories and consisted of palm oil, high-oleic safflower oil, and high-linoleic safflower oil, respectively. During the third and fourth week of each dietary period, multiple samples of blood were taken and were analyzed for plasma total cholesterol (TC), triglycerides (TG), and cholesterol in lipoprotein fractions (VLDL-C, LDL-C, and HDL-C). Twelve of the patients had normal TG levels; in these patients, both Mono and Poly diets caused statistically significant and equal lowerings of plasma LDL-C, but the Poly diet lowered HDL-C levels more frequently than did the Mono diet. Neither diet changed the level of plasma TG. The proportions of total protein and the various lipid components in isolated fractions (VLDL, IDL, LDL, HDL) were not altered by the two diets. Eight patients had hypertriglyceridemia; these individuals showed considerable variability in response to Mono and Poly diets. Although there was a trend towards reductions in TC and LDL-C levels by both types of unsaturated fats, the changes were inconsistent; furthermore, HDL-C concentrations were low on the Sat diet and were unaffected by either the Mono or the Poly diet. The results of this study show that oleic acid is as effective as linoleic acid in lowering LDL-C levels in normo-triglyceridemic patients, and oleic acid seemingly reduces HDL-C levels less frequently than does linoleic acid. Neither type of unsaturated fat had striking effects on lipoprotein levels of hypertriglyceridemic patients.

Liquid formula diet for human metabolic studies.

A liquid formula diet for use in studies with human subjects has been developed. All of the components can be obtained readily from commercial sources. For preparation of the diet, only equipment that customarily is found in institutional kitchens is needed. Acceptability over periods of several months is manifested by a large number of patients who consumed the liquid formula diet as their sole source of food.

Relationships of nutrient intake to lipids and lipoproteins in 1234 white children. The Lipid Research Clinics Prevalence Study.

Using the geographically and socioeconomically varied collaborative Lipid Research Clinics Prevalence Study data, this report focuses upon relationships between dietary intake and plasma lipids and lipoproteins in 1234 white children, 661 boys and 573 girls, aged 6-19 years who were sampled in a random recall (Visit 2) from large populations in six Lipid Research Clinics. Using multiple regression analysis, we found that in 6- to 12-year-old boys the dietary polyunsaturated-to-saturated fat ratio was inversely associated with plasma total and low density lipoprotein cholesterol and dietary cholesterol was positively associated with plasma high density lipoprotein cholesterol. In 13- to 19-year-old boys, high density lipoprotein cholesterol and the ratio of high density lipoprotein cholesterol to total cholesterol were inversely related to sucrose intake. In 6- to 12-year-old girls, plasma triglycerides were positively related to dietary sucrose. Using analysis of covariance in children having the lowest, middle, and top decile nutrient intakes, we found that higher carbohydrate intakes were associated with lower plasma total cholesterol in boys. The highest polyunsaturated fat intake (in 6- to 12-year-old girls) was associated with the lowest plasma cholesterol and very low density lipoprotein cholesterol. The highest cholesterol intake (in 6- to 12-year-old boys) was associated with the highest high density lipoprotein cholesterol levels. In girls, the highest sucrose intakes were associated with the highest plasma triglyceride levels. We conclude that the weak, but statistically significant, associations that we observed were meaningful relative to etiologies of nutrient-lipoprotein interrelationships, and should be useful in forming new hypotheses for focused metabolic ward studies.

Optimizing the effect of plant sterols on cholesterol absorption in man.

During three experimental periods, nine adults were hospitalized on a metabolic ward and fed a meal containing 500 mg of cholesterol as a component of scrambled eggs. In addition, the meal contained: 1) no additive, 2) 1 g beta-sitosterol, or 3) 2 g beta-sitosteryl oleate. Stools for the succeeding 5 days were analyzed to determine the percentage of the cholesterol in the test meal that was absorbed. The addition of beta-sitosterol resulted in a 42% decrease in cholesterol absorption; the beta-sitosteryl oleate caused a 33% reduction. These results indicate that the judicious addition of beta-sitosterol or beta-sitosteryl oleate to meals containing cholesterol-rich foods will result in a significant decrease in cholesterol absorption, with a consequent decrease in plasma cholesterol.

The absorbability by rats of various triglycerides of stearic and oleic acid and the effect of dietary calcium and magnesium.

Rats were fed diets in which the triglycerides contained oleate and stearate as the sole fatty acids. These fatty acids were esterified to specific positions on the glycerol molecule. The triglycerides were 1-stearoyl diolein (SOO), 2-stearoyl diolein (OSO), 2-oleoyl distearin (SOS), 1-oleoyl distearin (OSS), and triolein (OOO). The absorbability of the fatty acid component was measured by the fat balance technique. Two diets, one sufficient and the other deficient in calcium and magnesium, were used. The oleic acid of all of the triglycerides was absorbed almost completely. The following values for the absorbability of the stearate component in the presence and in the absence of the divalent cations were obtained: OSO 98 and 99; SOO 55 OAND 96; SOS 37 and 70; OSS 59 and 60. These patterns of absorbability are discussed in relation to the pathway of triglyceride digestion. If the stearic acid is esterified at the 2-position of the triglyceride, the resulting 2-monostearin is well absorbed. If it is esterified at the 1- or 3-position, it is released as free stearic acid, and in the presence of calcium and magnesium it is poorly absorbed.

The effect of a non-absorbable fat, sucrose polyester, on the metabolism of vitamin A by the rat.

Sucrose polyester (SPE) is a fat-like material that is not absorbed. The effect of this material on vitamin A metabolism was determined by measuring the amount of the vitamin that was stored in the liver of rats following the ingestion of a known amount of vitamin A. In one study, the vitamin A was administered as an oral dose in a vehicle consisting of various proportions of cottonseed oil and SPE. Each 1% replacement of cottonseed oil by SPE resulted in a 0.26% decrease in the amount of vitamin A found in the liver. In the second study, the vitamin A was incorporated into diets in which the fat component consisted of various proportions of cottonseed oil and SPE. When these diets were consumed for 1 week, each 1% replacement of cottonseed oil by SPE resulted in a 0.84% decrease in the storage of vitamin A by the liver. It is proposed that in the lumen of the intestine vitamin A distributes between the customary micellar phase and the unhydrolyzed oil phase of SPE. The vitamin A in this latter phase is eliminated in the feces.

Effect of an aqueous phase on the solubility of cholesterol in an oil phase.

In the absence of water, the solubility of cholesterol in triolein at 21 degrees C was 2.8%. When water was added to the system, the solubility of cholesterol in the oil phase decreased to 1.9%, and cholesterol monohydrate precipitated. The precipitation of the sterol evidently resulted from the excess concentration of the surface-active cholesterol at the interface, allowing the rapid interaction of water with cholesterol and the resulting formation of cholesterol monohydrate with its attendant lower energy and less soluble crystalline lattice. The ternary phase diagram for the system cholesterol--triolein--water, modified to include cholesterol monohydrate formation with the consequent decrease in sterol solubility; differs from the previously reported phase diagram. Other cholesterol--oil--aqueous systems related to biologically important lipids were studied. Cholesteryl oleate was more soluble than cholesterol in triolein (23% at 21 degrees C), and this value did not decrease when water was present. Water caused cholesterol to precipitate from cholesteryl linoleate at 37 degrees C. Thus crystalline cholesterol may be present in lipids found in atherosclerotic plaques at a lower concentration of free cholesterol than had been predicted previously. In another experiment, a micellar taurocholate solution precipitated cholesterol from triolein and from corn oil. These effects of aqueous systems suggest the possibility of cholesterol precipitation from dietary fat when it becomes mixed with water in the diet or stomach, or with the micellar phase in the intestine. Plant sterols were precipitated also from oil solutions by an aqueous phase. Water-induced sterol precipitation is a phenomenon that could occur in a variety of biological systems, and may be applicable to sterols in general.

Short term study of sucrose polyester a nonabsorbable fat-like material as a dietary agent for lowering plasma cholesterol.

The efficacy, safety, and acceptability of sucrose polyester (SPE), a fat-like material that is neither digested nor absorbed, were assessed in 13 normal and seven hypercholesterolemic subjects for its potential as a cholesterol-lowering agent. Addition or substitution of SPE for culinary fats in the diets of the normocholesterolemic individuals produced a mean reduction of total and low-density lipoprotein cholesterol of 14 and 17%, respectively (P less than 0.001), despite the daily ingestion of a diet containing 800 mg of cholesterol and of dietary fat with a P/S ratio of 0.4. Total and low-density lipoprotein cholesterol were not significantly reduced by similar 10-day feeding periods of SPE in seven subjects with familial hypercholesterolemia. High-density lipoprotein cholesterol and triglycerides were not changed in normal or hypercholesterolemic subject receiving SPE. Plasma vitamin A and E levels were reduced by 10 and 21% (p less than 0.02 and less than 0.001) in both normal and hypercholesterolemic subjects on SPE. These returned to the basal levels when SPE consumption was discontinued. SPE was recovered quantitatively (greater than 97%) in the stools, with the last measurable SPE being found day 3 to 5 after cessation of SPE intake. Despite recovery of 50 g or more of unhydrolyzed SPE in stools during SPE feeding, there was no clinical or chemical steatorrhea. On subtracting SPE's input to total stool fatty acids, it was found that "non-SPE" fatty acids in the stool had not increased during SPE feeding, SPE was easily incorporated into routine foodstuffs in addition to, or in substitution for, conventional dietary fats. On the basis of this short term evaluation in humans and other investigations with the rat and dog. SPE appears to have potential as a cholesterol-lowering agent.

The effect of a nonabsorbable lipid, sucrose polyester, on the absorption of dietary cholesterol by the rat.

The absorption of cholesterol from diets containing various proportions of triglycerides and an unabsorbable fat, sucrose polyester (SPE), was determined in rats. Each replacement of 1% dietary triglyceride with SPE resulted in a 1.2% decrease in cholesterol absorption. The SPE was a mixture of the hexa-, hepta- and octa-esters of long chain fatty acids. The physical properties of this material are similar to those of the usual dietary triglycerides. Relative to these studies, cholesterol was found to be equally soluble in triolein or SPE. If water was present as well, the solubility of the sterol was decreased by the same amount in both fats. The distribution coefficients of cholesterol between an oil phase of either triolein or SPE and a micellar phase simulating that found in the lumen of the intestinal tract were identical. These two types of fats differ in that SPE is neither digested nor absorbed. The decrease in cholesterol absorption is attributed to the continued presence of an oil phase of SPE in the lumen of the intestine. Dietary cholesterol distributes itself between this oil phase and the micellar phase. That portion in the oil phase is not absorbed but is egested in the feces.

Effect of hydrogenated fat on the plasma cholesterol and triglyceride levels of man.

A group of 33 adult males was fed for 21 days a formula diet that supplied 38 per cent of their calories as fat. The fatty acid composition of the diet was 25 per cent saturates, 16 per cent polyunsaturates and 58 per cent monounsaturates. All of the unsaturated acids were in the cis configuration. The subjects were then divided into two groups. One group of 17 men continued on the same diet. In the diet of the remaining subjects, 80 per cent of the dietary fat was replaced with a hydrogenated fat. Over 60 per cent of the monounstaurated acids and approximately one-half of the polyunsaturated acids of the diet of this latter group were in the trans configuration. Except for the presence or absence of trans acids, the fatty acid intakes of the two groups were the same. Over the 4-week period that the two diets were consumed, the group receiving the hydrogenated fat showed no change in plasma cholesterol or triglyceride levels relative to the subjects consuming the unhydrogenated fat. It is concluded that the effect of a hydrogenated fat on blood lipid level is determined by its fatty acid composition and this effect is not altered by the isomeric form of the unsaturated acids.