Cholesterol vehicle in experimental atherosclerosis. III. Effects of absence or presence of fatty vehicle

Three separate experiments show that cholesterol administered to rabbits in the absence of added fat is more atherogenic than cholesterol fed together with corn oil. When cholesterol is dissolved in the corn oil (by heating) prior to mixing with the diet, it is more atherogenic than when it is suspended in the oil. In every case the lowest serum and liver cholesterol levels were observed in the group not receiving corn oil. Gas chromatography of the fatty acids of the serum cholesterol esters of pooled sera suggest that there are smaller amounts of unsaturated C₁₈ fatty acids in the cholesterol-no fat group. Deficiency in these unsaturated acids may be the cause of the high atherogenicity of the cholesterol-no fat diet. There is also a lower proportion of unsaturated fatty acids in the triglycerides of this group. Heating of corn oil 10 min, at 160–200(°C.) causes an increase of titratable fatty acid in the oil (0.005 m-equiv./g. to 0.088 m-equiv./g. or 0.14% FFA to 2.5% FFA). The relatively large amounts of free unsaturated fatty acids in the heated oil may be the cause of the greater atherogenicity of the solution, as compared to the suspension, of cholesterol in corn oil. Presented at the 33rd Fall Meeting, American Oil Chemists’ So ciety, Los Angeles, Calif., September 28–30, 1959. This work was supported by grants from the National Institutes of Health (H-3299 and A-2131), The Nutrition Foundation Inc., and The John A. Hart-ford Foundation Inc.     

Dietary fat and fatty acids modulate cholesterol cholelithiasis in the hamster

We tested two hypotheses, i) whether the type and the amount of fat in the diet will affect the formation of cholesterol gallstones in the hamsters, and ii) whether palmitic acid, a major fatty acid component of butterfat, can act as a potentiator of cholesterol cholelithiasis in the hamster. Young, male golden Syrian hamsters (Sasco) were fed a semipurified diet containing casein, corn starch, cellulose and cholesterol (0.3%) to which various types and amounts of fat (butterfat, olive oil, menhaden oil, corn oil) were added. All diets contained 2% corn oil to supply essential fatty acids to the growing hamsters. No deaths or illness occurred during the experiment. Animals fed the semipurified diet plus 4% butterfat (group 1) had a gallstone incidence of 63%. Replacement of butterfat with either olive oil, corn oil or menhaden oil prevented the formation of cholesterol gallstones entirely (groups 2–4). When total butterfat was increased from 4% to 8% (group 8), the incidence of cholesterol gallstones increased to 80%. Substitution of 4% olive oil (group 5), corn oil (group 6), or menhaden oil (group 7) for the additional 4% butterfat significantly reduced gallstones to 35%, 45% and 30%, respectively. The replacement of 4% butterfat with 1.2% palmitic acid gave the highest incidence of cholesterol gallstones (95%). These results suggest that butterfat (and one of its components, palmitic acid) intensifies gallstone formation in this model whereas mono- and polyunsaturated fats act as inhibitors of cholesterol cholelithiasis. A fatty acid, possibly palmitic acid, appears to act as lithogen in our model.     

The effect of fat on the gastric responses to foods

Summary 1. In eight series of triplicate tests on persons in good health and with normal secretory responses who were fed test meals of foods cooked with fat, the day to day variations in gastric evacuation times ranged from 0 to 30 minutes with an average deviation from the mean of ±17 minutes. 2. Experiments with meals of foods in which moderate quantities of fats were incorporated intimately by either baking or frying according to good culinary procedure revealed no relationship between the fat contents of the foods and the times required for complete evacuation of the foods from the subjects’ stomachs. 3. The experiments indicated a parallelism between the protein contents of the test meals and the gastric evacuation times. 4. No significant differences were observed between the influences of a hydrogenated vegetable fat and of butter upon the rates of evacuation from the subjects’ stomachs of meals of potatoes in which these fats had been incorporated intimately by good culinary technic. Within the limits of error of the experimental procedure, French fried and Lyonnaise potatoes containing moderate amounts of fat were evacuated from the stomachs as rapidly as boiled potatoes. 5. Gastric emptying times for meals of doughnuts did not differ significantly from gastric evacuation times for meals of bread and butter supplying equivalent amounts of fat. 6. The addition to a test meal of glucose in water of either hydrogenated vegetable fat or butter fat in amounts equivalent to two-thirds the weight of the glucose retarded the evacuation of the glucose meal from the stomach. 7. Excess fat, added to potatoes by pan-frying in hydrogenated vegetable fat or butter to the extent of making the potatoes “greasy,” such as may occur in poor culinary practice, prolonged the emptying time of the stomach beyond the period for boiled potatoes. 8. An explanation has been suggested for this retardation of the emptying of the stomach effected both by digestible fats added to glucose solutions and by foods containing fats in excess of that which is incorporated intimately in these foods by good culinary methods. This paper was presented before the meeting of the American Oil Chemists’ Society, Chicago, Illinois, October 27, 1944. This work was supported by a grant from Lever Brothers Company, Cambridge, Massachusetts.     

Synthesis and estimation of calorific value of a structured lipid-potential reduced calorie fat

The majority of reduced calorie fats and fat substitutes avaiable, today, though similar in texture and flavor to natural fats, contain fatty acids that are not usually present in edible oils and fats and thus do not fully match the chemistry and functions of natural fats. For example, such products do not provide nutritionally important essential fatty acids (EFA). In this investigation, we prepared and evaluated a reduced calorie fat, prepared entirely from natural fats, taking advantage of the fact that long-chain saturated fatty acids (LCSFA), such as behenic acid (22∶0), are poorly absorbed. Mustard oil (MO) and sunflower oil (SO) were used as substrates to yield a structured lipid (SL). The product, being derived from a natural vegetable oil, would thus provide EFA, as would a native fat, a feature not provided by the low-calorie fats available in the market. Erucic acid (22∶1) was isolated from MO by a lipase (EC 3.1.1.3)-catalyzed reaction. It was then hydrogenated to behenic acid, the ethyl ester of which was subsequently enzymatically transesterified with SO to yield a plastic fat containing about 30–35% behenic acid. Absorption of this fat was studied in Wistar rats. In a preliminary single oral dose experiment, rats were fed equal amounts (2 mL) of SO and the SL. Plasma triacylglycerol (TAG) levels were estimated after 1, 2, and 3 h of feeding. The significantly lower concentration of plasma TAG in the 2-h sample, observed in the SL-fed group compared to the SO-fed group (P<0.001), indicated poor absorption of the SL. In order to estimate the calorific value of the SL, we conducted a restricted diet growth experiment over 21 d on weanling Wistar male rats with SO as caloric control. Diets for the test groups were modified by adding 5, 10, and 15% SO for the control groups, and 5 and 10% SL for the experimental groups. Food consumption of the test groups was restricted to 50% of the feed containing 5% SO that had been consumed by the ad libitum group the previous day. Body weights were recorded during the experiment. Calorific value of the SL was estimated by comparing the 21st-d mean body weight gain of the control group with that of the experimental group. Estimated calorific value of the SL was 5.36 kcal/g. Most of the behenic acid fed was excreted, as indicated by the analysis of the fatty acids of plasma and fecal total lipid. A second growth experiment on ad libitum diet was conducted over 21 d on weanling Wistar male rats to compare the absorption behavior of the SL with that of natural oil. SO (10%) was added to the diet of the control group, and SL (10%) was added to the diet of the experimental group. Feed consumption, as well as body weights, was recorded during the experiment. The growth pattern of the experimental group was identical to that of the control group during the period of study. The mean feed intake (9.8 g/d/rat for the control group vs. 9.9 g/d/rat for the experimental group) indicated good palatability of the product. In conclusion, the enzymatically synthesized SL containing EFA and natural antioxidants has nutritional properties almost identical to those of natural fats, and can be used as a reduced calorie fat.     

Effects of dietary fats on fatty acid composition and Δ5 desaturase in normal and diabetic rats

We have studied the effect of various diets on the phospholipid fatty acid composition andin vitro Δ5 desaturase activity of hepatic microsomes derived either from the normal or streptozotocin-induced diabetic rat. The diets studied were the standard rat chow diet and a basal fat-free diet supplemented either with 20 percent saturated fat, 20 percent unsaturated fat, or 20 percent menhaden oil. Phospholipid fatty acid composition analysis revealed that the normal rat fed the saturated fat or menhaden oil diet had significantly decreased arachidonate levels, consistent with decreased Δ5 desaturase activities and decreased 18∶2n−6 intake. On the contrary, the unsaturated fat diet decreased dihomo-γ-linolenate and increased arachidonate levels, without increased Δ5 desaturase activity. Streptozotocininduced diabetes resulted in decreased arachidonate and Δ5 desaturase activity. The unsaturated fat diet fed to the diabetic rat also failed to correct this decreased Δ5 desaturase activity. The unsaturated fatty acids in this diet also displaced a substantial amount of n−3 fatty acids in both normal and diabetic microsomes, due to the competition between these two fatty acid families for incorporation into the membrane phospholipids. Conversely, the menhaden oil diet fed to the normal and diabetic rats displaced n−6 fatty acids, reduced Δ5 desaturase activity, and enhanced 22∶6n−3 incorporation into diabetic microsomes.     

Effects of level and type of dietary fat on incidence of mammary tumors induced in female sprague-dawley rats by 7,12-dimethylbenz(α) anthracene

Female Sprague-Dawley rats on semisynthetic diets containing 10% and 20% by weight of corn oil developed more mammary adenocarcinomas after treatment with a single oral dose of 7,12-dimethylbenz(α)anthracene than similar rats on diets containing only 0.5% or 5% corn oil. Experiments with 10 different fats and oils fed at the 20% level indicated that unsaturated fats enhance the yield of adenocarcinomas more than saturated fats. Fibroadenomas and adenomas were also found in small numbers in all dietary groups but the yield did not seem to be influenced by level or type of dietary fat. The possible relevance of these findings to the incidence of breast cancer in humans is discussed. Presented at the ISF-AOCS World Congress, Chicago, September 1970.     

Effect of acute ethanol ingestion on fat absorption

A test meal (300 mg casein, 600 mg sucrose, 100 mg corn oil, tracer dose of 9.10³H oleic acid) was given to fasting adult rats with intestinal lymph fistulas. One group received an acute oral dose of ethanol (3.2 g/kg body weight) simultaneously with the test meal. Controls received 2.5 ml of water instead of ethanol. Ingestion of ethanol temporarily delayed the removal of lipid radioactivity from the stomachs. More than 25% of radioactivity fed remained 8 hr after feeding whereas with control rats less than 10% of lipid radioactivity fed remained 6 hr after feeding. In controls and ethanoltreated rats, the amounts of exogenous lipids in the intestinal lumen and mucosa were low and similar enough. Quantities of endogenous and exogenous lipids found in the lymph collected during 24 hr after feeding were similar in the two groups, but the fat absorption peak was found after 6 hr in alcoholic rats and before 6 hr in controls. This delay was probably due to the retention of lipids in the stomach. More of the exogenous lipid was always transported by small particles moving in the region of α₁ globulins in cellulose acetate electrophoresis than by larger particles remaining at the origin. This proportion was enhanced in the ethanoltreated animals. The larger fat particles were richer in endogenous fatty acids in alcohol-treated rats than in controls. These experiments are a part of a thesis of “Doctorat d'Etat” (Speciality: Biology) n^o C.N.R.S. A0 11.965 presented in Dijon on February 6, 1976.     

Effects of ionizing radiation on some vegetable fats

The volatile compounds produced by irradiation, under vacuum at 6 megarads, in five vegetable fats were analyzed qualitatively and quantitatively by gas chromatography and mass spectrometry. A series of compounds,n-alkanes, 1-alkenes, internally unsaturated alkenes, alkadienes, alkatrienes, alkanals and methyl and ethyl esters of fatty acids, were identified in each of the fats studied. A wide variation occurs in the amounts of the volatiles produced from each fat. The major radiolytic products were few in number and were found to depend largely on the fatty acid composition of the fat. These compounds were essentially the hydrocarbons containing one or two carbon atoms less than the component fatty acids. This relationship was found consistent if radiolytic products of fats with different fatty acid compositions are compared or if the fatty acid composition of the same fat is altered by hydrogenation. The results correlate well with those of earlier studies on simple triglycerides.     

The effect of dietary fat level and quality on plasma lipoprotein lipids and plasma fatty acids in normocholesterolemic subjects

This study examined the effect on the plasma lipids and plasma phospholipid and cholesteryl ester fatty acids of changing from a typical western diet to a very low fat (VLF) vegetarian diet containing one egg/day. The effect of the addition of saturated, monounsaturated or polyunsaturated fat (PUFA) to the VLF diet was also examined. Three groups of 10 subjects (6 women, 4 men) were fed the VLF diet (10% energy as fat) for two weeks, and then in the next two weeks the dietary fat in each group was increased by 10% energy/week using butter, olive oil or safflower oil. The fat replaced dietary carbohydrate. The VLF diet reduced both the low density lipoprotein (LDL)-and high density lipoprotein (HDL)-cholesterol levels; addition of the monounsaturated fats and PUFA increased the HDL-cholesterol levels, whereas butter increased the cholesterol levels in both the LDL- and HDL-fractions. The VLF diet led to significant reductions in the proportion of linoleic acid (18∶2ω6) and eicosapentaenoic acid (20∶5ω3) and to increases in palmitoleic (16∶1), eicosatrienoic (20∶3ω6) and arachidonic acids (20∶4ω6) in both phospholipids and cholesteryl esters. Addition of butter reversed the changes seen on the VLF diet, with the exception of 16∶1, which remained elevated. Addition of olive oil resulted in a significant rise in the proportion of 18∶1 and significant decreases in all ω3 PUFA except 22∶6 compared with the usual diet. The addition of safflower oil resulted in significant increases in 18∶2 and 20∶4ω6 and significant decreases in 18∶1, 20∶5ω3 and 22∶5ω3. These results indicate that the reduction of saturated fat content of the diet (<6% dietary energy), either by reducing the total fat content of the diet or by exchanging saturated fat with unsaturated fat, reduced the total plasma cholesterol levels by approximately 12% in normocholesterolemic subjects. Although the VLF vegetarian diet reduced both LDL- and HDL-cholesterol levels, the long-term effects of VLF diets are unlikely to be deteterious since populations which habitually consume these diets have low rates of coronary heart disease. The addition of safflower oil or olive oil to a VLF diet produced favorable changes in the lipoprotein lipid profile compared with the addition of butter. The VLF diets and diets rich in butter, olive oil or safflower oil had different effects on the 20 carbon eicosanoid precursor fatty acids in the plasma. This suggests that advice on plasma lipid lowering should also take into account the effect of the diet on the fatty acid profile of the plasma lipids.     

Composition,particle size and role in dietary fat transport of two different lipoproteins of the intestinal lymph

Rat intestinal lymph very low density lipoproteins have been separated by cellulose acetate electrophoresis. After administration of a meal including natural fats and labeled fatty acids, two labeled bands were detected on the electrophoregraphs. Further separations of these two kinds of particles were performed by density gradient zonal centrifugation. The isolated lipoproteins were analyzed for chemical composition and investigated by electron microscopy and electrophoresis. The moving particles had a higher protein and cholesterol content and a smaller diameter than the particles which remained at the origin. It has also been shown that the major part of the labeled lymph lipids were transported by the smaller particles.     

Effect of oxidized oil on lipogenic enzymes

Male Wistar rats were fed for 4 wk on diets containing 2% oxidized corn oil. Liver tissue was then studied to determine the effect of feeding peroxidized oil on lipogenic enzymes. Although substances which reacted with thiobarbituric acid increased in liver microsomes and mitochondria with increasing peroxide values of the dietary corn oil fed, the activities of glucose-6-phosphate dehydrogenase, malic enzyme and acetyl-CoA carboxylase in liver were unchanged. However, when rats were fed for 2 wk on diets containing 10% fat, of which 0.5, 5 or 10% was unoxidized corn oil and the remainder was hydrogenated beef tallow filler, the lipogenic enzyme activities and also the liver triglyceride levels were observed to decrease with increasing amounts of dietary corn oil. Therefore, although a synthetic diet containing corn oil was easy to oxidize spontaneously, the reductions of lipogenic enzymes in rats fed the diet would not have been caused by lipid peroxides but by unsaturated fatty acids themselves.     

Effect of Fatty Acid Composition of Monoglycerides and Shear on the Polymorph Behavior in Water-in-Palm Oil-Based Blend

Effect of the fatty acid composition of monoglycerides and shear on the polymorphic behavior in a water-in-oil (W/O) emulsion semi-solid fats blend was investigated. The bulk fat blend and the W/O emulsion fat blend with added either unsaturated or saturated monoglycerides were prepared using a rapid cooling heat exchanger, and the polymorphic transitions from β′ to β-form during storage were compared by X-ray diffraction. The peak intensity of the β-polymorph of the samples with added saturated monoglycerides was stronger than that of unsaturated monoglycerides, and the peak intensity of the β-polymorph of the W/O fat blend emulsions was stronger than that of the bulk fat blends. The polymorphic transition to the β-form during storage of the W/O emulsion fat blend was promoted by the applied shear. In contrast, that of the bulk fat blend was retarded by shear. These results suggested that fatty acids, which combined to monoglycerides on the surface of water droplets, influenced the polymorph transformation of the fat crystal network in a continuous semi-solid fat phase because of the acyl–acyl interactions between the fatty acid residues of the monoglycerides and triacylglycerols in the fat crystal network.     

The influence of dietary medium chain triglycerides on rat mammary tumor development

The N-nitrosomethylurea rat mammary tumor model was used to compare the tumor-promoting effects of a highfat (HF) diet containing a 3:1 mixture of medium chain triglycerides (MCT) and corn oil with that of a HF and a low-fat (LF) corn oil diet. The serum and tumor lipid content and fatty acid (FA) composition were also determined in the three dietary groups. It was found that the MCT-containing diet failed to promote tumor development compared with the HF corn oil group. Tumor incidence in the HF-MCT group was similar to that of the LF corn oil group (5% fat, w/w), but significantly decreased compared to the HF corn oil group. Total serum cholesterol levels were significantly depressed in the HF corn oil group compared to the HF-MCT and LF corn oil groups. Analysis of serum and tumor FA profiles indicated that the HF corn oil group exhibited approximately twice the amount of linoleic acid (LA) as the other two treatment groups. Differences among the three groups in the major FA metabolite of LA, arachidonic acid, were minimal. These results are consistent with the hypothesis that tumor promotion by dietary fat is more a function of the type than the amount of fat ingested. In addition, they indicate that MCT, due at least in part to their unique structural and physiological properties, exert markedly different effects on mammary tumor development than conventional long chain unsaturated fatty acids. Presented at the symposium on “Specialty Lipids and Their Biofunctionality” at the annual meeting of the American Oil Chemists' Society, Philadelphia, May 1985.     

Fatty acid compositions of lipids from corn and grain sorghum kernels

Summary Characteristics and fatty acid compositions of the lipid components of the main fractions (germ, starch, gluten, and fiber) obtained in the wet milling of corn and grain sorghum kernels have been determined. The various lipids exhibited differences in chemical characteristics and fatty acid composition. These differences were found to be similar in both grains. Germ fats were the most unsaturated, contained the least free fatty acids and the least unsaponifiable matter. Starch fats were 70 to 90% free fatty acids and contained large amounts of palmitic acid. Gluten and fiber fats contained up to 32% unsaponifiables and about 20% free fatty acids.     

The effect of dietary fat on the glyceride structure of rat carcass fat

Carcass fats were obtained from weanling rats fed a complete diet for 8 weeks, which consisted of 2% cottonseed oil and 10% of the following fats: (1) corn oil; (2) the fatty acids of corn oil; (3) triricinolein; (4) ricinoleic acid; (5) the hydrogenated fatty acids of castor oil ; and (6) commercial hydrogenated shortening. The fats were subjected to both pancreatic lipase and nonspecific hydrolysis ; the resulting acids converted into methyl esters by conventional methods, and subjected to gas Chromatographie analysis. From these data, the positional distri-bution of the component fatty acids, glyceride types, and isomeric forms were calculated. The results indicated a preferential placement of un-saturated acids in the 2- position of the carcass triglycerides and that the carcass fat composition in terms of unsaturated (U) and saturated (S) fatty acid composition is not greatly influenced by the S and U compositions of the dietary fat. It was found that hydroxy acids or their tri-esters are metabolized much the same as are normal triglycerides and exert no particular in-fluence upon the fat structure of the rat. Some type of relationship between the dietary U and the U₃ in the carcass fat appears to be present. The glycerides of the carcass fats examined here are essentially a random mixture of the major glyceride types, but the isomeric forms (SUS, S SU, USU and UUS) are a definite non-random mixture. Carried out at the Food Res. Div., Armour & Co., and at The Burnsides Research Laboratory under research grant No. EF 225 from the National Institutes of Health, U. S. Public Health Service, and Deparmtent of Health, Education, and Welfare.     

Effect of dietary fat on phospholipid class distribution and fatty acid composition in rat fat cell plasma membrane

The effect of dietary fats on phospholipid class distribution and fatty acid composition was studied in rat fat cell plasma membrane. Three groups of male Wistar weanling rats were fed for 8 wk three diets differing in the amount and nature of the fats: 1.5% sunflower oil (low fat control; LFC), 10% sunflower oil (high fat, unsaturated; HFU), 1.5% sunflower oil+8.5% cocoa butter (high fat, saturated; HFS). Plasma membranes were prepared from epididymal adipocytes. The amount and type of dietary fat significantly altered membrane phospholipid distribution. Phospholipid content was lowered with HFU as compared to LFC or HFS diets, but no changes were observed for cholesterol. Phosphatidylinositol (PI) and phosphatidylserine (PS) were less affected by dietary changes than were other phospholipid classes. Major changes were detected for phosphatidylcholine (PC), phosphatidylethanolamine (PE) and sphingomyelin (SM) contents. No large changes in PC and PE fatty acid compositions were observed between the LFC and HFS groups, but the HFU diet induced several changes. Correlations with plasma membrane 5′-nucleotidase activities are discussed.     

Prevention of cholesterol cholelithiasis by dietary unsaturated fats in hormone-treated female hamsters

We examined the effect of diet on gallstone incidence and the composition of biliary phosphatidylcholines in methyltestosterone-treated female hamsters. These hamsters were fed a nutritionally adequate purified lithogenic diet containing 2% corn oil, 4% butterfat, 0.3% cholesterol, and 0.05% methyltestosterone, resulting in a cholesterol gallstone incidence of 86%. This incidence was lowered when mono-and polyunsaturated fats or fatty acids were added to the diet: 2.5% oleic acid resulted in total prevention of cholesterol cholelithiasis, 2.5% linoleic acid, and 4% safflower oil (78% linoleic acid content) reduced gallstone incidence to 26 and 8%, respectively. An additional 4% butterfat (29% oleic acid content) produced gallstones in 50% of the animals. At the end of the 6-wk feeding period, the bile of all hamsters was supersaturated with cholesterol. The major biliary phosphatidylcholine species in all groups were (sn-1-sn-2): 16:0–18:2, 16:0–18:1, 18:0–18:2, 16:0–20:4, and 18:2–18:2. The safflower oil-and linoleic acidfed hamsters exhibited an enrichment of 16:0–18:2 (16–18%); added butterfat or oleic acid increased the proportion of 16:0–18:1 (9 and 25%, respectively). We conclude that the phosphatidylcholine molecular species in female hamster bile can be altered by dietary fats/fatty acids and that mono-and polyunsaturated fatty acids play a role in suppressing the induced cholelithiasis.     

Triglyceride composition of bovine milk fat with elevated levels of linoleic acid

The effect of increasing the linoleic acid (18∶2) content of milk fat on the composition and structure of the triglycerides (TG) was investigated. Protected sunflower seed supplement was added to the diet of a cow grazing on pasture, and the structure and composition of the milk fat compared with the milk fat from its monozygous twin which had been fed a control diet. The relative proportions of TG fractions of high, medium, and low molecular weight in the milk fat with elevated levels of 18∶2 (15.5% 18∶2) were 43.0, 19.5, and 37.5 moles %, respectively, compared with 36.1, 19.7, and 44.2 moles %, respectively, in the milk fat from the cow fed the control diet. Separation of these three TG fractions of each milk fat into TG classes with different levels of unsaturation showed that the milk fat with elevated levels of 18∶2 contained higher proportions of diene, triene, and tetraene TG and correspondingly lower proportions of saturated and, to a lesser extent, monoene TG. The saturated and monoene TG from the two milk fats had similar fatty acid compositions. However, the diene TG of the 18∶2-rich milk fat included high proportions of the combination of 18∶2 with two saturated fatty acids (FA) which are minor constituents of normal milk fats. Likewise, the triene TG reflected the presence of 18∶2 in combination with 18∶1 and a saturated FA.     

Dietary fat composition and tocopherol requirement: IV. Safety of polyunsaturated fats

In a long-term multigeneration study, conducted in our laboratories for 32-years, with occasional longevity and histopathological evaluations included, rats of our own inbred strain (originally of Wistar derivation) were fed semisynthetic diets comprising whole wheat, skim milk powder, and fat in the form of margarine products. The total source of tocopherols was the dietary fat itself. Saturated fatty acid content (S) remained relatively constant at about 20% of the fat and total tocopherol level also remained constant at about 0.12% of the fat. Polyunsaturated fatty acid (P) content, however, progressively increased almost fourfold, from 7.5% to 28.5% and alphatocopherol levels decreased to one-half level, from 0.033% to 0.016% of the fat. Hence, the ratio of polyunsaturated fatty acids to alpha-tocopherol content changed markedly from 227∶1 to 1780∶1, with other factors (relative to fat composition) held constant during the 32-year period of feedings and observations. Fat level in the diet increased over the years from 9.2% to 16.0% or from about 21% to about 33% of the caloric intake. Thus, quality and quantity of the fat in the diet progressively changed, and the impact of these changes was evaluated by comparing biological performances of the successive generations. Growth and reproduction and lactation performances were noted to be regularly satisfactory and comparable from generation to generation throughout the experimental period. Longevity studies conducted on arbitrarily selected generations also provided data showing no deleterious effects associated with a dietary change. Histopathological examinations of tissue revealed minimal myocarditis and no malignant tumors which could be attributed to a dietary factor. No vitamin E deficiencies were observed. Even the in vitro peroxide hemolysis values for the red blood cells of the animals, fed the diets containing the higher levels of polyunsaturated fatty acids, were low, indicating that the dietary fats provided sufficient absorbable tocopherol to protect the potentially oxidizable unsaturated fatty acids in the erythrocyte membrane. Biochemical data reflected responses to aging and not to any specific diet fed. It is concluded that a diet providing as much as 33% of the calories as a fat, the latter containing up to 28.5% polyunsaturated fatty acids, substantially of the essential fatty acid type, with a P/S ratio of up to 1.6∶1 and a polyunsaturated fatty acid to alphatocopherol ratio as high as 1780∶1] produces no undesirable effects in the rat. Presented in part at a symposium entitled “Long Term Nutritional Effects of Dietary Fats” at the International Society for Fat Research World Congress, September 30, 1970, Chicago, Illinois.     

Species variation in the atherogenic profile of monkeys: Relationship between dietary fats,lipoproteins, and platelet aggregation

Because lipoproteins and platelet aggregation have been implicated in atherogenesis, relative differences in the response of these variables to dietary fat saturation were compared in three species of monkeys differing in their susceptibility to atherosclerosis (cebus, rhesus, and squirrel monkeys). Both long-term (8–12 years) and short-term (8 weeks) responses to diets containing 31% fat calories were examined in the same monkeys. As expected, long-term feeding of coconut oil by comparison to corn oil produced significantly higher plasma concentrations of total cholesterol, LDL cholesterol, apoB, and triglycerides, as well as higher ratios of LDL/HDL cholesterol and apo B/apo A-I. These responses were characteristic of all species with cebus being most responsive and rhesus the least. The shortterm plasma cholesterol response to animal fats (butter, lard, beef tallow) was significantly less than that to coconut oil. When fish oil was substituted for two-thirds of either corn oil or coconut oil, exceptional decreases occurred in plasma cholesterol and triglycerides, as well as in HDL cholesterol and apo A-I concentrations despite the fact that the fish oil diets contained more saturated fat and less polyenes than the corn oil diet. Platelet aggregation tended to increase with saturated fat consumption and greatly decreased with fish oil intake in all monkeys, although cebus monkeys were ten-fold more resistant to platelet aggregation than the other two species. The molecular species of platelet phosphatidylcholine (PC) varied with both the dietary fat fed and species of monkey. An inverse correlation (r=−0.60; p<0.001) was found between changes in one such PC molecular species (18∶0−20∶4) induced by diet and the platelet aggregation threshold. These results demonstrate that the lipemic and platelet responses to dietary saturated fat depend upon both the type of fat (i.e., the specific combination of dietary fatty acids, including the chain length of saturated fatty acids and the degree of polyunsaturation) and the species of monkey (genetic component) in which the response is elicited.