Dietary CLA affects lipid metabolism in broiler chicks

A total of 120 three-wk-old broiler chicks were randomly assigned to three diets containing 0, 2, or 3% CLA and fed for 5 wk. Fat content and FA composition of liver, plasma, and feces were analyzed. Key enzymes involved in FA synthesis and catabolism in liver, TG, cholesterol, and FFA content of plasma were also determined. Dietary CLA increased TG, total cholesterol, and HDL cholesterol levels in plasma. The increased plasma TG level could be caused by increased FA synthesis in the liver after CLA feeding, because the activity of FA synthase in the liver increased after dietary CLA treatment. Dietary CLA changed the FA composition of feces but had no effect on fat content. Compared to the amounts of linoleic and linolenic acids present in the control diet, the amounts excreted into the feces of CLA-treated birds were significantly higher. Liver weights of broilers significantly increased after CLA feeding, but there was no difference in liver fat content among the different CLA treatments. CLA treatment did not influence total FFA content in plasma; however, there was a significant difference in the composition of FFA. Dietary CLA reduced the content of linoleic and arachidonic acids in both plasma and liver.     

Low-fat diets do not lower plasma cholesterol levels in healthy men compared to high-fat diets with similar fatty acid composition at constant caloric intake

In most studies reporting the effects of high-fat (HF) and low-fat (LF) diets on human plasma fatty acids (FA) and lipoprotein levels, the design involved adding to the diet an oil that had an FA composition (FAC) very different from the FAC of the control diet. Thus, it is difficult to determine if simply reducing the fat content of the diet without changing the dietary FAC changes the tissue FAC or alters plasma lipid levels. In this study, we fed diets that contained either 22 or 39% of calories from fat, but had no differences in their FAC, for 50 d to a group (n=11) of healthy men (20–35 y). Thus, the polyunsaturated/saturated ratios (1.0) of the diets were identical as were the n−3/n−6 ratio and the monounsaturated-to-total fat ratios. The diets contained (wt% of total fat) approximately 28% saturated FA, 33% monounsaturatedcis-FA, 6% monounsaturatedtrans-FA, 22% n−6 polyunsaturated FA, and 7% n−3 polyunsaturated FA, and 4% other minor FA. The diets consisted of natural foods and were formulated to contain 16 en% protein, either 45 or 62 en% carbohydrate (CHO) and at least the recommended dailyallowance for all micronutrients. Both diets contained 360 mg of cholesterol per day. All subjects were given the HF diet for 20 d, and then six were placed on the LF and the other five remained on the HF diet for 50 d. The two groups were crossedover for the remaining 50 d of the study. The subjects' baseline total cholesterol level was 173 mg/dl, after 50 d on the HF diet it was 177 mg/dl and after 50 d on the LF diet, 173 mg/dl. The differences were not significant, and there were no significant changes in either the LDL or HDL cholesterol levels with either diet. Triglyceride levels, and consequently very low density lipoprotein levels, rose significantly on the LF, higher CHO diet compared to the levels found in the subjects on the HF diet (91.5 and 66.4 mg/dl respectively,P<0.002). The linoleic acid content of the plasma, platelets, and red blood cells was significantly (P<0.05) reduced in the LF diet compared to HF diet, without any obvious physiological effects. Hence, many earlier observations indicating reductions in plasma lipid levels when people are on LF diets may be due to changes in the FAC of the diet, not the reduction in fat calories.     

Influence of stearic acid on hemostatic risk factors in humans

Stearic acid has been claimed to be prothrombotic. Elevated plasma factor VII coagulant activity (FVIIc) may raise the risk of coronary thrombosis in the event of plaque rupture. Fibrinogen, an acute-phase protein, is necessary for normal blood clotting; however, elevated levels of fibrinogen increase the risk of coronary heart disease (CHD). Here I report the results of three controlled, human dietary intervention studies, which used a randomized crossover design to investigate the hemostatic effects of stearic acid-rich test diets in healthy young men. A diet high in stearic acid (shea butter) resulted in a 13% lower fasting plasma FVIIc than a high palmitic acid diet, and was 18% lower than a diet high in myristic and lauric acids (P=0.001) after 3 wk of intervention. The stearic acid-rich test fat increased plasma fibrinogen concentrations slightly compared with the myristic-lauric acid diet (P<0.01). When investigating the acute effects of fatty meals, those high in stearic acid (synthesized test fat) resulted in a smaller postprandial increase in FVII than those high in trans and oleic FA, indicating a smaller increase in activated FVII after ingesting stearic acid compared with fats high in monounsaturated FA, probably caused by lower postprandial lipemia. Thus, the present investigations did not find dietary stearic acid to be more thrombogenic, in either fasting effects compared with other longchain FA, or in acute effects compared with dietary unsaturated FA, including trans monounsaturated FA. The slightly increased effect on fasting plasma fibrinogen may be biologically insignificant, but it should be investigated further.     

Separate effects of dietary protein and fat on serum cholesterol levels: another view of amino acid content of proteins

Casein or soy protein with vegetable or animal fat were used to determine the dietary protein or fat effects and their possible interaction on serum cholesterol levels. Young, male New Zealand white rabbits with a mean weight of 2.1 kg were divided into groups of six and fed one of four different diets containing 20% of the calories as protein, 30% as fat (according to dietary guidelines for the United States) and 50% as carbohydrate. The diets contained casein or soy (lysine/arginine ratio = 2.2 or 0.9, respectively) as the protein sources with fat from either almond oil or butter. There was no significant difference in weight gain among the diet groups. Total serum cholesterol level was highest among animals fed the diet containing butter with casein (177 +/- 25 mg/dl) or soy protein (189 +/- 50 mg/dl), it was intermediate in animals fed the vegetable oil with casein (121 +/- 14 mg/dl), and lowest in the soy protein with vegetable oil group (58 +/- 12 mg/dl). There was a significant difference in serum cholesterol levels due to the protein effect when vegetable oil was used (p less than 0.05) but not with butter. There was also a significant fat effect on serum cholesterol when the diet contained soy protein (p less than 0.005) but not when the protein was casein. No significant interaction was observed between the dietary fat and protein sources on serum cholesterol levels, which suggests that dietary protein and fat independently affect the levels of serum cholesterol. Thus, dietary protein has a significant effect on serum cholesterol levels and may be a factor in the low levels of serum cholesterol observed among vegetarians and in humans of Third World countries where the diets is primarily of vegetable origin.     

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.     

The hypercholesterolemic effect of dietary coconut fatversus corn oil in hypo- or hyperresponsive rabbits is not exerted through influencing cholesterol absorption

In two inbred strains of rabbits with high or low response of plasma cholesterol to dietary saturatedversus polyunsaturated fatty acids, the efficiency of intestinal cholesterol absorption was measured. The feeding of a cholesterol-free purified diet containing saturated fatty acids in the form of coconut fat, when compared with a diet containing corn oil as polyunsaturated fatty acids, did not influence the efficiency of cholesterol absorption in the two rabbit strains. Irrespective of the dietary fat source, the hyperresponsive rabbits absorbed cholesterol more efficiently. It is concluded that the hypercholesterolemic effect of dietary coconut fatversus corn oil is not exerted by influencing cholesterol absorption.     

The relationship of corn oil and animal fats to serum cholesterol values at various dietary protein levels

Summary A high level of dietary protein lowered serum cholesterol. Incorporation of increasing amounts of beef tallow did not increase the serum cholesterol levels significantly, and some dietary fat was found to be desirable. Addition of up to 0.3% of dietary cholesterol did not significantly increase the serum cholesterol levels on either low or high levels of dietary fat or protein. The energy protein (E/P) ratio of a diet had a significant effect on serum and carcass cholesterol levels. The type of fat had an effect on serum cholesterol levels, but with lowering of the E/P ratio this effect became negligible. Presented at the 32nd Annual Fall Meeting, American Oil Chemists' Society, October 21, 1958, Chicago, Ill. The work was supported by research grant No. H-1819 from the National Institute of Health, U. S. Public Health Service, Department of Health, Education and Wealfare. Portion of a thesis to be presented by M. G. Kokatnur as partial fulfillment of the requirements for the degree of Doctor of Philosophy in Food Technology.     

The types of circulating fatty acids influence vascular reactivity

The objective of this study was to investigate the relationship between the composition of FA in serum lipids, a marker of dietary fat intake, and vascular reactivity using a combination of cross-sectional and intervention approaches. Fifty-six middle-aged subjects were evaluated in a cross-sectional protocol regarding the relationship between the proportion of FA in serum cholesterol esters and vascular reactivity using measurements of forearm blood flow (FBF) with venous occlusion plethysmography during hyperemia. Another 19 middle-aged subjects were given a rapeseed oil-based diet rich in mono-and polyunsaturated FA or a control diet rich in saturated FA during two consecutive 4-wk periods separated by a 4-wk washout period. In the cross-sectional protocol, the FA 18:0 and 20:3 were positively related to resting FBF, whereas an inverse relationship was seen for the FA 20:5 and 22:6 (P<0.05−0.01). Opposite relationships were seen between these four FA and the relative increase in maximal FBF during hyperemia (P<0.05−0.01). In the intervention protocol, the saturated diet increased resting FBF, as well as the relative increase in maximal FBF during reactive hyperemia, compared to the diet rich in unsaturated FA (P<0.05). Both the cross-sectional and intervention data support the view that the composition of serum FA, which at least partly reflects the quality of dietary fat, plays a role in determinations of vascular reactivity.     

Maternal Dietary Fat Affects Milk Fatty Acid Profile and Impacts on Weight Gain and Thermogenic Capacity of Suckling Rats

We aimed to assess the effects of maternal supplementation with the main fat sources used in the human Western diet (olive oil, butter, margarine) on milk FA composition and on plasma FA profile of offspring, and to determine whether it may influence body-weight-gain (BWG) and adiposity of offspring during the suckling period. Wistar rats were supplemented with the different fat sources from day 14 of gestation and throughout lactation. Olive oil-supplemented dams showed the highest proportion of oleic-acid in milk, with no changes in plasma. Their offspring also showed the highest proportion of this FA in plasma, lower BWG during the suckling period, and higher levels of UCP1 in brown adipose tissue (BAT) at weaning. Margarine-supplemented dams showed the highest percentage of PUFA in milk, and a similar tendency was found in plasma of their offspring. Butter-supplemented dams displayed higher proportion of saturated FA (SFA) in milk compared to other fat-supplemented dams, but lower than controls. Control offspring also showed higher proportion of SFA in plasma and greater BWG during the suckling period than fat-supplemented groups. Significant correlations were found between the relative content of some milk FA and BWG of offspring, in particular, oleic-acid levels correlated negatively with BWG and positively with UCP1 levels. These results show that maternal dietary source of fat affects milk FA composition and circulating FA profile, as could be expected, but also BWG and thermogenic capacity of offspring during the suckling period. An effect of oleic-acid stimulating BAT thermogenic capacity of suckling pups is proposed.     

Diet and cholesteremia

The statistical correlation between elevated serum cholesterol levels and increased risk of coronary heart disease has channeled thinking towards regarding dietary fat and cholesterol as the principal causes of hypercholesteremia. Since 1909 there have been a number of changes in nutrient availability in the United States. Protein availability is unchanged but the ratio of animal to vegetable protein rose from 1.06 in 1909 to 2.37 in 1972. Fat availability has risen by 26% with the ratio of animal to vegetable fat falling from 4.88 in 1909 to 1.64 in 1972. A review of available data indicates that amount and type of protein may affect cholesteremia and atherosclerosis in experimental animals. Soy protein is less cholesteremic than casein but the extent of difference can be affected by the type of carbohydrate. In a semi-purified, cholesterol-free diet, saturated fat exerts an atherogenic effect but unsaturated fat does not. No atherogenicity is evident when saturated fat is added to laboratory ration. In the semipurified diet, fructose is more atherogenic than glucose, and casein is more atherogenic the soy protein. The latter difference can be virtually eliminated if alfalfa raplaces cellulose as the ditary fiber. The data suggest that all elements of the diet interact and can affect cholesteremia and atherosclerosis. These effects must be considered in the planning of dietary intervention trials.     

Betaine supplementation affects the cholesterol but not the lipid profile of pigs

This study was undertaken to investigate the effects of long term betaine intake on the cholesterol and lipid profile of Alentejano (AL) pigs. At ?36 kg body weight (BW), castrated male and female pigs fed a commercial (C) diet, were divided into two groups: i) Group C, consuming the C diet; and ii) Group CB, consuming the C diet supplemented with 1 g/kg betaine. Pigs were slaughtered at ?100 kg BW. Fasting plasma concentrations of protein, urea, glucose, TAG, phospholipids, homocysteine, total and LDL‐ and HDL‐cholesterol were determined. Liver TAG, phospholipids, and total and free cholesterol were analyzed, as well as total lipids, cholesterol contents, and fatty acid (FA) composition of M. semimembranosus and dorsal subcutaneous fat. Betaine supplemented pigs presented significantly higher plasma concentrations of TAG, phospholipids, cholesterol, and lipoprotein cholesterol. Dorsal subcutaneous fat cholesterol concentration was also significantly higher in CB than in C pigs. No differences were detected in the most abundant FA profile (including the unsaturated to saturated FA ratio) of muscle and subcutaneous fat tissues among treatments. These data suggest that betaine induces dyslipidemia, and increases cholesterol concentration in dorsal subcutaneous fat, without affecting the FA profile of M. semimembranosus and dorsal subcutaneous fat.     

Effects of diet and high density lipoprotein subfractions on the removal of cellular cholesterol

The effects of isocaloric substitutions of dietary polyunsaturated and saturated fat on the composition and function of plasma high density lipoproteins (HDLs) were studied in 3 normal subjects who were fed saturate-rich and polyunsaturate-rich diet programs. Compared to the saturated diets (P/S=0.4), polyunsaturated fat diets (P/S=4 or 2) reduced both plasma cholesterol and triglyceride levels. In 2 of the subjects, HDL cholesterol concentrations increased with polyunsaturated fat caused a reduction in HDL fatty acyl content of oleate and an increase in linoleate. To determine whether the altered composition affected the removal of cell membrane cholesterol, HDL and their subfractions, HDL₂ and HDL₃, which were isolated from each of the diets, were incubated with Ehrlich ascites cells in vitro. The cells were prelabeled with [³H] cholesterol, and the release of labeled cholesterol from the cells into the medium containing the various HDL fractions was determined. HDL, irrespective of the type of dietary fat, caused a release of [³H] cholesterol from the cells into the medium. The amount of [³H] cholesterol recovered in the medium was dependent on the absolute concentration of HDL cholesterol added to the cells and was independent of the type of diet. These results indicate that HDL facilitates the removal of cholesterol from cells, but that the amount and rate of removal are independent of the changes in HDL composition that can be obtained by dietary perturbations.     

Dietary Fatty Acid Composition Modulates Obesity and Interacts with Obesity-Related Genes

The prevalence of obesity is skyrocketing worldwide. The scientific evidence has associated obesity risk with many independent factors including the quality of dietary fat and genetics. Dietary fat exists as the main focus of dietary guidelines targeting obesity reduction. To prevent/minimize the adipogenic effect of dietary fatty acids (FA), intakes of long‐chain saturated‐ and trans‐FA should be reduced and substituted with unsaturated FA. The optimal proportions of dietary unsaturated FA are yet to be defined, along with a particular emphasis on the need to achieve a balanced ratio of n‐3:n‐6 polyunsaturated FA and to increase monounsaturated FA consumption at the expense of saturated FA. However, inter‐individual variability in weight loss in response to a dietary intervention is evident, which highlights the importance of exploring gene–nutrient interactions that can further modulate the risk for obesity development. The quality of dietary fat was found to modulate obesity development by interacting with genes involved in fatty acid metabolism, adipogenesis, and the endocannabinoid system. This review summarizes the current knowledge on the effect of the quality of dietary fat on obesity phenotype and obesity‐related genes. The evidence is not only supporting the modulatory effect of fat quality on obesity development but also presenting a number of interactions between obesity‐related genes and the quality of dietary fat. The identified gene–FA interaction may have a clinical importance and holds a promise for the possibility of using genetically targeted dietary interventions to reduce obesity risk in the future.     

N‐Stearoylethanolamine Restores Pancreas Lipid Composition in Obesity‐Induced Insulin Resistant Rats

This study investigates the protective effect of N‐stearoylethanolamine (NSE), a bioactive N‐acylethanolamine , on the lipid profile distribution in the pancreas of obesity‐induced insulin resistant (IR) rats fed with prolonged high fat diet (58 % of fat for 6 months). The phospholipid composition was determined using 2D thin‐layer chromatography. The level of individual phospholipids was estimated by measuring inorganic phosphorus content. The fatty acid (FA) composition and cholesterol level were investigated by gas–liquid chromatography. Compared to controls, plasma levels of triglycerides and insulin were significantly increased in IR rats. The pancreas lipid composition indicated a significant reduction of the free cholesterol level and some phospholipids such as phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer) compared to controls. Moreover, the FA composition of pancreas showed a significant redistribution of the main FA (18:1n‐9, 18:2n‐6, 18:3n‐6 and 20:4n‐6) levels between phospholipid, free FA, triglyceride fractions under IR conditions that was accompanied by a change in the estimated activities of Δ9‐, Δ6‐, Δ5‐desaturase. Administration of N‐stearoylethanolamine (NSE, 50 mg/kg daily per os for 2 weeks) IR rats triggered an increase in the content of free cholesterol, PtdCho and normalization of PtdEtn, PtdSer level. Furthermore, the NSE modulated the activity of desaturases, thus influenced FA composition and restored the FA ratios in the lipid fractions. These NSE‐induced changes were associated with a normalization of plasma triglyceride content, considerable decrease of insulin and index HOMA‐IR level in rats under IR conditions.     

Effects of diets rich in saturated fatty acids with or without added cholesterol on plasma lipids and lipoproteins

Semi-synthetic diet I which contained 16% hydrogenated coconut oil and 5% cholesterol, and diet II, identical to I but without cholesterol supplement, were fed to dogs for four months to determine the effects of added cholesterol on lipemia produced by diets high in saturated fatty acids (FA) and lacking essential FA. In addition, diet I was fed to another group of dogs for 12 to 16 months. The initiation of lipemia was very similar in all experimental animals. Plasma from dogs on diets I and II showed significant increases in lipid concentration and changes in FA per cent composition within the first week, as compared to controls, while during the first month there was no difference in lipid concentration or FA distribution in all lipid fractions between I and II. At the 10th and 16th weeks plasma total and free cholesterol and phospholipid were significantly higher in the group on diet I, with the cholesterol supplement, than on diet II with no added cholesterol, but there was no difference in triglyceride concentration between these groups. Dogs on diet I for 12 to 16 months showed a further and substantial increase in plasma FA concentration; these changes were most marked in cholesteryl esters. Little or no lipoprotein with electrophoretic and ultracentrifugal properties of alpha-lipoprotein was present in the plasma. Immunotechniques showed that it was present. The composition of dietary FA had great influence in producing this hyperlipemia. Lipemia produced was not a simple reflection of the FA in these diets as evidenced by the increase in some FA, e.g., C_16∶1, which was absent in the experimental diets and C_18∶1, which contributed only 3.4% of the FA. Large increases in palmitoleate and oleate indicate synthesis or mobilization or both from other tissues. Diets composed predominantly of saturated medium chain length fatty acids, with or without added cholesterol were equally effective in the initiation of hyperlipemia. Data also suggest that added cholesterol is necessary for sustaining hyperlipemia. Presented in part at the AOCS Annual Meeting, New Orleans, April 1970.     

Differential effects of dietary linoleic and α-linolenic acid on lipid metabolism in rat tissues

Comparative effects of feeding dietary linoleic (safflower oil) and α-linolenic (linseed oil) acids on the cholesterol content and fatty acid composition of plasma, liver, heart and epididymal fat pads of rats were examined. Animals fed hydrogenated beef tallow were used as isocaloric controls. Plasma cholesterol concentration was lower and the cholesterol level in liver increased in animals fed the safflower oil diet. Feeding the linseed oil diet was more effective in lowering plasma cholesterol content and did not result in cholesterol accumulation in the liver. The cholesterol concentration in heart and the epididymal fat pad was not affected by the type of dietary fatty acid fed. Arachidonic acid content of plasma lipids was significantly elevated in animals fed the safflower oil diet and remained unchanged by feeding the linseed oil diet, when compared with the isocaloric control animals fed hydrogenated beef tallow. Arachidonic acid content of liver and heart lipids was lower in animals fed diets containing safflower oil or linseed oil. Replacement of 50% of the safflower oil in the diet with linseed oil increased α-linolenic, docosapentaenoic and docosahexaenoic acids in plasma, liver, heart and epididymal fat pad lipids. These results suggest that dietary 18∶2ω6 shifts cholesterol from plasma to liver pools followed by redistribution of 20∶4ω6 from tissue to plasma pools. This redistribution pattern was not apparent when 18∶3ω3 was included in the diet.     

Response of free and esterified plasma cholesterol levels in the mongolian gerbil to the fatty acid composition of dietary lipid

The present study was undertaken to investigate the potential suitability of the Mongolian gerbil as a useful animal model to study the effects of dietary fats on plasma cholesterol levels. Semipurified diets containing either 20% lard, 20% safflower oil, or 19.5% beef tallow +0.5% safflower oil were equalized to contain 0.01% cholesterol and 0.05% plant sterol and were fed for a four week experimental period. The proportions of total calories contributed by fat, protein and carbohydrate (starch/sucrose ratio of 2∶1) were 40, 14 and 46%, respectively, so as to approach the distribution of calories within the average North American diet. Free, esterified, and total plasma cholesterol levels of male gerbils were determined weekly by gas liquid chromatography after drawing blood via a serial sampling technique. After 1, 2, 3, and 4 weeks of feeding the experimental diets, total cholesterol levels were lowest in the safflower oil fed animals; the corresponding values were 19–64% greater in gerbils fed lard and 68–91% greater in those consuming the beef tallow diet. Cholesterol in the free form generally responded more dramatically to the type of dietary lipid than did cholesterol in the ester form. Irrespective of the type of dietary lipid or the length of the feeding trial, 18–23% of the total plasma cholesterol was in the free form and 77–82% was present as the ester. In view of the similarity to the human of the relative proportions of free versus esterified cholesterol, the type of cholesteryl esters, and their response to dietary manipulation, the gerbil appears to be a useful animal model for studying the regulatory effect of dietary lipid on plasma cholesterol levels. Presented in part at the A.O.C.S. Annual Meeting, San Francisco, CA, May 1979.     

Effect of struture and form on the ability of plant sterols to inhibit cholesterol absorption in hamsters

We investigated the effect of three types of plant sterols (4-desmethylsterols, 4,4′-dimethylsterols, and pentacyclic triterpene alcohols) in three forms (free, esterified with FA, or with phenolic acids) on cholesterol absorption. Plant sterol fractions derived from soybean (99% 4-desmethylsterols), rice bran (70% 4,4′-dimethylsterols), or shea nut (89% pentacyclic triterpene alcohols) were fed to male hamsters (n=20/group) as free sterols or esterified with FA or phenolic acids (cinnamic or ferulic). Cholesterol absorption was measured after 5–8.5 (mean, 7) wk by a dual-isotope technique. Soybean sterol intake significantly reduced cholesterol absorption efficiency (23%) and plasma total cholesterol (11%). Rice bran sterols tended to lower cholesterol absorption efficiency by 7% and plasma total cholesterol by 5%, whereas shea nut sterols had no effect. In hamsters, dietary 4-desmethylsterols were more effective than 4,4′-dimethylsterols in lowering cholesterol absorption and levels of cholesterol in blood. Pentacyclic triterpene alcohols had no effect on the absorption of cholesterol or on its level in blood. Esterification with FA did not impair the ability of 4-desmethylsterols and 4,4′-dimethylsterols to inhibit cholesterol absorption, whereas esterification with phenolic acids reduced this ability. This study supports the use of 4-desmethylsterols, esterified with FA to increase solubility, as the most effective cholesterol-lowering plant sterols in the diet.     

Vitamin E,cholesterol, and lipids during atherogenesis in rabbits

Rabbits were fed diets including cholesterol and 10% butterfat to determine whether polyunsaturated butter (9% 18∶2) would be less atherogenic than normal saturated butter (3% 18∶2) when fed for 12 weeks. The cholesterol diets alone, 0.5% or 2%, produced aortic plaque development, and plasma cholesterol increased 20 times, lipids increased 10 times, and vitamin E increased 5 times. The inclusion of both fat and cholesterol in the diet produced a synergistic effect, doubling these values to 40 times for cholesterol, 20 times for lipids, and 10 times for vitamin E. The higher circulating levels of cholesterol caused increased tissue levels of cholesterol. With 2% cholesterol and fat, liver and aorta cholesterol increased 10 times, heart 4 times, and muscle cholesterol 2 times. The lower 0.5% dietary cholesterol load was successful in limiting the amount of tissue cholesterol increase. Liver, aorta, heart, and muscle levels of cholesterol were only about half the concentration attained when 2% cholesterol was fed. It was concluded that there were no differences in plasma or tissue cholesterol, vitamin E, or atherosclerosis attributable to the polyunsaturated nature of the diet. The 10% butterfat diets alone, whether saturated or unsaturated, did not induce aortic plaques and did not increase blood or tissue cholesterol, lipids, or vitamin E. Our results suggest that the lipid mobilizing effect is mediated by cholesterol, probably by conversion to bile acids and a stimulation in intestinal absorption.     

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.