Serum lipids, lipoprotein composition and liver cholesterol in genetically obese Zucker rats fed semipurified diets containing either casein or soy protein

The effect of semipurified diets containing either casein or soy protein on serum lipids, lipoprotein composition and liver cholesterol was studied in genetically obese Zucker rats. The ingestion of a cholesterol-enriched semipurified diet containing casein resulted in elevated levels of serum cholesterol and phospholipids compared to the feeding of a soy protein diet. No differences in serum triglycerides were observed. Differences in serum cholesterol and phospholipids were mainly reflected in the very low density lipoproteins and low density lipoproteins and to a minor extent in the high density lipoproteins. Liver cholesterol paralleled the levels of cholesterol in the serum, the rats fed casein exhibited markedly higher levels of liver cholesterol than those fed soy protein. Furthermore, the rats fed casein also had enlarged livers. Thus, this study clearly shows the differential cholesterolemic effect of dietary casein and soy protein in genetically obese Zucker rats.     

The hypocholesterolemic action of the undigested fraction of soybean protein in rats

Soybean protein was exhaustively digested with endo- and exo-type microbial proteases and the effect of the digestible low molecular fraction (LMF) and the undigested high molecular fraction (HMF) on the serum cholesterol level was compared to that of the intact protein in rats given a cholesterol-enriched diet. The HMF, peptides relatively abundant in hydrophobic amino acids, was found to be substantially hypocholesterolemic when fed at the nitrogen level equivalent to that of the 20% soybean protein diet, and not only serum but also liver cholesterol levels were similar to those usually encountered in rats given diets free of cholesterol. There was a dose-dependent reduction of serum and liver cholesterol when casein was replaced stepwise with HMF. The cholesterol-lowering action could be attributable to an increased fecal steroid excretion.     

Relationship between magnesium and zinc levels of the diet and its protein utilization

Protein utilization of the diet was tested in relation to different levels of magnesium and zinc in rats. The experimental diets contained either a low (0.14 g Mg or 10 mg Zn/kg) or adequate (0.45 g Mg or 40 mg Zn/kg) level of Mg or Zn and two different quality protein sources: casein or wheat gluten. Net protein utilization and net protein radio indexes in case of casein were significantly lower for the diet containing a low level of Mg or Zn. For gluten diets, such differences were not observed. Digestibility of protein measured in rats fed a low Mg or Zn casein diet was the same as for the diets with an adequate content of these minerals. Rats fed low Mg or Zn casein diets showed a significantly lower plasma Mg or Zn and a lower liver DNA content in comparison to the rats on adequate Mg or Zn diets. The results indicate that the utilization of protein is affected by Mg and Zn content of the diet and that this relationship depends on the quality of protein.     

Effects of cholesterol-free, semipurified diets containing different levels of casein or soy protein on distribution of cholesterol and protein among serum lipoproteins of rabbits

Rabbits fed cholesterol-free, low-fat, semipurified diets have more cholesterol and protein in serum low density lipoprotein (LDL) relative to high density lipoprotein (HDL) than rabbits fed Chow diet. This difference was accentuated by a casein semipurified diet but was also observed with a soy protein diet even though the latter did not produce an elevation of serum cholesterol. To investigate the reason for these differences, the formulation of the semipurified diets was altered by reducing the level of protein from 27 to 16%, increasing the fat from 1 to 4% and the fiber from 5 to 13%, to correspond more closely to the proportions in Chow. With this formulation, the soy protein diet gave a lipoprotein pattern similar to that of Chow, whereas the casein diet produced a moderately elevated serum cholesterol level with more cholesterol in LDL than in HDL. When the protein in the newly formulated diets was increased back to 27%, the lipoprotein patterns reverted to those obtained with the original formula. In this case, soy protein-fed rabbits had moderately elevated serum cholesterol whereas casein-fed animals showed hypercholesterolemia. These results indicate that the altered lipoprotein pattern observed previously in rabbits fed semipurified diets is related to the high level of protein in those diets.     

The effects of dietary cholesterol upon the hypercholesterolemia of pregnancy

The hypercholesterolemia which accompanies the normal human pregnancy is not known to be influenced by diet or other factors. The present experiment in fourteen pregnant women was designed to document this phenomenon under controlled metabolic conditions and to study the effect of dietary cholesterol upon this usual increase in serum cholesterol. The subjects included twelve normal subjects, one juvenile diabetic, and one type II familial hypercholesterolemic subject. They were fed controlled, nutritionally adequate diets which were equivalent except for the cholesterol content, which was cholesterol-free or 600–1000 mg from egg yolk daily. Calories were adjusted to permit weight gain of 1.4 kg per mo. The cholesterol-free diet lowered the mean serum cholesterol level in the 12 normal pregnant women from 234-187 mg/dl, a 20% decrease (?47 ± 37 S.D.) (p < 0.005). The addition of cholesterol to the diet invariably elevated the mean serum cholesterol concentrations to 223 mg/dl, a 19% increase (+36 ± 12) (p < 0.001). The mean serum triglyceride levels increased steadily throughout pregnancy regardless of diet, up to 198 ± 43 (S.D.) mg/dl at term. Both serum cholesterol and triglyceride concentrations decreased strikingly 1 wk after parturition. These serum cholesterol and triglyceride responses occurred similarly in the familial hypercholesterolemic and the diabetic women. The increased serum cholesterol levels during the high cholesterol diets occurred largely in the low density lipoprotein (LDL) fraction. Despite the inevitable alterations of cholesterol and lipooprotein homeostasis which occur in pregnancy, the results of this study indicated that the usual hypercholesterolemia of pregnancy in women eating the general American diet was greatly ameliorated by a very low cholesterol, nutritionally adequate diet.     

Cholesterol-free diet and the physiologic hyperlipidemia of pregnancy in familial hypercholesterolemia

Longitudinal studies of the effects of a cholesterol-free diet and a less rigid 300 mg/day low cholesterol diet, both with a polyunsaturated to saturated fatty acid ratio of $\text{1.8}\text{1}$, were carried out preconception, during gestation, and postpartum in a woman heterozygous for familial hypercholesterolemia. On the cholesterol-free diet, during weeks 8–14 of gestation, plasma cholesterol was lowered 25% (from 310 to 230 mg/dl), and plasma low density lipoprotein cholesterol (C-LDL) (from 240 to 160 mg/dl), 33%. The 25% reduction in plasma cholesterol was slightly more than prviously reported decrements of 19% in 14 normal women during pregnancy, also receiving a cholesterol-free diet. The 300 mg cholesterol diet was not as hypocholesterolemic as the cholesterol-free diet. Its maintenance throughout gestation limited the within-pregnancy increments of total plasma cholesterol and C-LDL to 21% (352–426 mg/dl) and 14% (286–326 mg/dl) respectively. Both the cholesterol-free and the 300 mg cholesterol diet were well tolerated, and should be nutritionally adequate for pregnant women, since they contain more than the recommended amounts of high quality protein, vitamins, minerals, and calories for pregnant women. Cholesterol restricted diets during pregnancy in familial hypercholesterolemics should reduce the physiologic hypercholesterolemia of pregnancy, and potentially reduce the increased risk of coronary heart disease relative to the degree and duration of elevations of total and LDL cholesterol.     

Influence of fish protein as compared to casein and soy protein on serum and liver lipids, and serum lipoprotein cholesterol levels in the rabbit

Serum and hepatic cholesterol and triglyceride levels, and serum lipoprotein cholesterol were investigated in rabbits fed fish protein as compared to casein and soy protein as part of a 20% protein, low fat, cholesterol-free, semi-purified diet. A nonpurified diet was used as a control. After a 28-day experimental period, rabbits fed casein developed hypercholesterolemia compared to those fed the soy protein diet. Serum cholesterol levels of rabbits fed fish protein was intermediate and not different from that of the casein or the soy protein group. However, serum triglycerides were higher in the fish group than in the casein group. Feeding of fish protein resulted in a reduction of hepatic cholesterol compared to casein, indicating no direct relationship between serum and hepatic cholesterol. In addition, fish protein induced a decrease of cholesterol in the low density lipoproteins (LDL) compared to casein and an increase of cholesterol in the high density lipoproteins (HDL) compared to casein and soy protein. Reduction in LDL-cholesterol (LDL-C) and elevation in HDL-cholesterol (HDL-C) caused a 10-fold decrease in the LDL-C/HDL-C ratio of fish protein fed rabbits compared to those fed casein. This ratio was similar to that observed with soy protein which was also lower than the ratio of the casein group. Thus, since the LDL-C/HDL-C ratio has been shown to be a good indicator of the atherosclerosis risk, these results suggest that fish protein, as well as soy protein, may reduce the risk of atherosclerosis in rabbits, compared to casein.     

Dihydrocapsaicin (DC) protects against serum hyperlipidemia in guinea pigs fed a cholesterol-enriched diet

Juvenile guinea pigs were maintained either on a standard diet (cholesterol-free) or a 0.5% cholesterol-enriched vitamin C deficient diet for six weeks. Half of the animals of each dietary group were treated with dihydrocapsaicin (DC) at the rate of 8 mg per animal per day. DC administration significantly altered food consumption, body weight, and dry weight of feces of animals maintained on the standard diet. In addition, the mean serum triglyceride concentration of these animals was significantly decreased with DC treatment. Food consumption, body weight and (wet) fecal weight of animals maintained on the 0.5% cholesterol-enriched diet were significantly lower than the corresponding values in control animals even though the liver was much larger in proportion to the total body weight. The mean serum cholesterol concentration of the animals fed a cholesterol-enriched diet was significantly elevated. However, in animals also receiving DC, the cholesterol and triglyceride levels were comparable to controls fed a regular diet. The gross and microscopic fatty infiltration of the liver observed in the cholesterol-fed animal were minimized in those animals fed cholesterol and DC.     

Dietary protein-dependent modification of serum cholesterol level in rats. Significance of the arginine/lysine ratio

Male rats were fed for 4 weeks cholesterol-free diets containing proteins from different sources, milk, fish, egg yolk, soybean, rice and peanut. The antihypercholesterolemic effect of vegetable proteins compared to animal proteins was certified. There was a negative correlation (gamma = -0.74) between the serum cholesterol level and the arginine/lysine ratio of dietary protein, suggesting a role of this ratio in determining the serum cholesterol level. In general, the fasting level of circulating insulin was lower whereas that of glucagon was higher on feeding vegetable proteins, thus resulting in a fall of the insulin/glucagon ratio. Changes in the hormonal status may be relevant to the protein effect.     

Compositional changes in serum lipoproteins during developing hypercholesterolemia induced in rabbits by cholesterol-free, semipurified diets

Changes in the concentration and composition of serum very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) were studied in rabbits transferred from chow diet to cholesterol-free, semipurified diets containing casein or isolated soy protein. The fat and fibre content of these diets was similar to that of chow but a higher protein level was used to enhance the hypercholesterolemia. During the first week on the casein diet, there was a marked increased in LDL-cholesterol, protein and phospholipids, and these higher levels were maintained during the subsequent 3 weeks of the study. Similar but less marked changes were obtained with the soy protein diet. The components of VLDL showed relatively little change after introduction of the diets to the animals. In both VLDL and LDL, the proportion of cholesterol increased and that of triglycerides decreased after 1 week on the casein diet and a similar trend was seen in HDL. The concentration of HDL-cholesterol showed little change but triglycerides, protein and phospholipids all tended to decline on both casein and soy protein diets.     

Influence of Dietary Protein Concentration and Quality on Response to Erythropoietin in the Polycythaemic Rat

S ummary . The effects were examined of dietary protein concentration and quality on the response of polycythaemic hypertransfused rats to 6 units of human urinary erythropoietin. Rats were either starved or fed one of 14 different diets. Four protein sources were used, having a quality gradient from 100 to about 24. Two proteins—casein and wheat gluten—were used at five different levels of concentration (5–25%) in the diet. The response of rats maintained on the standard diet (Purina rat chow, 23.4% protein/g) was taken as the normal standard. The response to erythropoietin was 25% of normal in starved rats and 35% of normal in rats put on a protein-free diet. When 10% protein in the diet was obtained by using high biological value proteins (egg yolk or casein) the response to erythropoietin was normal. When the same concentration was achieved by using low biological value proteins (wheat gluten or corn protein) the response to erythropoietin was undistinguishable from that of rats put on the protein-free diet. When rats were maintained on diets with different concentrations of casein (5–25%) a normal response was observed when protein concentration was 10% with no further changes at higher concentrations. When rats were fed diets with different wheat gluten concentrations (5–25%) the response to erythropoietin was subnormal. These data suggest that the ability of rats to respond normally to erythropoietin is dependent on a continuous dietary intake of proteins at levels which are dependent on their biological values.     

Effects of casein and soy protein on hepatic and serum lipids and lipoprotein lipid distributions in the rat

Rats fed a semipurified diet containing casein developed higher levels of circulating triglycerides and cholesterol than animals fed a soy protein-containing diet. The increased serum lipid levels in non-fasted rats were associated largely with the d less than 1.006 g/ml lipoprotein particles (e.g. chylomicrons or very low density-like lipoproteins). In addition, casein-fed rats exhibited higher levels of circulating insulin and depressed hepatic 7 alpha-hydroxylase levels compared to soy-fed rats. Supplementation of the casein diet with arginine, to give an arginine/lysine ratio comparable to that in the soy diet, resulted in a reduction of d less than 1.006 g/ml lipids, a reduction in serum insulin levels and an elevation in hepatic 7 alpha-hydroxylase activity. Supplementation of the soy diet with lysine also resulted in modification of these parameters toward those observed with casein diets, albeit the effects were less dramatic. The results suggest that the hyperlipidemia associated with feeding casein-based diet is associated with decreased rates of clearance of chylomicron-like lipoproteins and their component triglycerides and cholesterol. Furthermore, this is largely prevented by addition of arginine to diets containing casein as the sole protein source.     

Intestinal apolipoprotein B-48 synthesis and lymphatic cholesterol transport are lower in swine fed high fat, high cholesterol diet with soy protein than with casein

Effects of dietary proteins on intestinal lipoproteins were studied in 8 Yorkshire swine fed a high fat, high cholesterol diet with either casein or soy protein. After 5 weeks of feeding, the casein group exhibited moderately elevated levels of serum cholesterol (334 +/- 46 mg/dl). The soy protein group showed significantly less hypercholesterolemia as compared to the casein group (122 +/- 8 mg/dl). Swine were subjected to cannulation of mesenteric lymph duct under halothane anesthesia. A single dose of 250 microCi [14C]cholesterol and 10 mCi [3H]leucine was infused into the upper jejunum 2 h after one-fifth of daily food was given. The 3-h lymphatic transport of cholesterol in casein-fed swine was significantly higher than in those fed soy protein. Triglyceride transport values were similar in the 2 groups. The [3H]leucine incorporation study revealed that transport of apo B-48 bore a significant positive relationship to transport of cholesterol in both chylomicron and VLDL fractions of mesenteric lymph. A greater apo B-48 secretion with higher specific activity was probably responsible for the greater transport of cholesterol in chylomicrons in casein-fed than in soy protein-fed swine. Similarly, the transport of lymph VLDL cholesterol in swine fed casein or soy protein paralleled the amount of accompanying apo B-48. Dietary proteins probably influence the intestinal synthesis of apo B-48 which in turn affects cholesterol transport into the lymphatics.     

Effects of soy protein and saponins on serum, tissue and feces steroids in rat

Four groups of rats were fed, for 45 days, one of the following semipurified diets containing sucrose 55% (w/w) and (a) casein 25%, (b) casein 24%, saponins (from Saponaria officinalis) 1%, (c) isolated soy protein 25%, (d) soy protein 24%, saponins 1%. The soy protein diet, compared to the casein one, produced an increase in the fecal excretion of neutral sterols on the 29th and 42nd days, without any modification in the liver, aorta and serum cholesterol concentrations. The effect of soy protein cannot be attributed to its saponin content but other substances associated to soy protein may interfere. With the casein diet, added saponins increased the fecal excretion of neutral sterols and bile acids and decreased liver and aorta cholesterol levels. Serum cholesterol was found unchanged. The effects of saponins were suppressed or greatly reduced with the soy protein diet. These results could be explained by binding of the sterols in insoluble forms.     

Hypolipidemic effects of high-carbohydrate, high-fiber diets

Serial measurements of serum cholesterol and triglyceride (TG) concentrations were performed in diabetic men fed high-carbohydrate, high-fiber (HCF) as well as high-carbohydrate, low-fiber (HCLF) diets. Fourteen lean men were first fed control diets for 1 wk and then fed weight-maintaining HCF diets (70% carbohydrate) that were restricted in fat and cholesterol. Average insulin doses dropped from 27 U/day on control diets to 12 U/day on HCF diets and fasting plasma glucose values were 26 mg/dl lower on HCF diets. On HCF diets, serum cholesterol values were lower by 32% (64 mg/dl, p < 0.001) than values on control diets. Fasting serum TG values were slightly lower on HCF diets but average postprandial TG values were significantly lower (p < 0.001) on HCF diets than on control diets. In another study, 11 men were fed two weight-maintaining 70% carbohydrate diets in an alternating sequence; one diet was high in plant fiber (HCF) and the other was low in plant fiber (HCLF). Insulin doses averaged 20 U/day on control diets and fell to 11 U/day (p < 0.01) on HCF diets or 12 U/day (p < 0.01) on HCLF diets. Fasting serum TG values were similar on the control and HCF diets; on HCLF diets fasting serum TG values were higher by 28% (37 mg/dl) than values on control diets (p < 0.01). Incorporation of generous amounts of plant fiber into the diet prevented the hypertriglyceridemic response to these high-carbohdrate diets. These studies also indicate that dietary maneuvers can be very effective in lowering serum cholesterol values in patients with diabetes mellitus.     

Protein quality evaluation in rats of typical diets for 4- to 6-year-old children from different socioeconomic areas living in Oaxaca, Mexico

Legumes and cereals are principal sources of energy and protein in developing countries. In Oaxaca, Mexico, corn is the primary agricultural crop, therefore corn tortillas and beans are the main energy and protein sources. The objective of this study was to evaluate the protein quality in rats of typical diets for 4- to 6-year-old children from different socioeconomic areas in Oaxaca, Mexico. Composite diets representing the typical diets were formulated and fed to male weanling rats for 10 days. A control diet using casein as the reference diet and one free of nitrogen were included in the study. The apparent protein digestibility was determined in rats using the chromic oxide marker technique and the data was statistically analyzed for differences between control and experimental diets. Rats fed the diet of low income children gained about 2 g/day compared to about 3.8 g/day for the rats fed the control (casein) diet and had the lowest weight gain/g of protein intake. The NPR was 3.52 compared to 4.31 for the control diet. This diet is 67% vegetable protein and 33% animal protein. The diet for the medium income group contained a higher percentage of animal protein, 76% and thus higher digestibility, 78%. The results of this study indicate that the protein quality of children's diets in Oaxaca, Mexico, need to be improved.     

Effect of feeding maize/legume mixtures on biochemical indices in rats

Protein-energy malnutrition is one of the major public health problems in developing countries of the world due to prevailing socio-economic problems. This study aimed to observe the effect of formulated complementary blends on biochemical parameters of rats. Extruded complementary blends from maize fortified with cowpea or soybean at a level of 35% and 25% respectively were fed to 4 groups of rats for 28 days. Similarly, 3 other groups of rats were placed on casein, non-protein or rat pellet diet. Biochemical analysis was done on blood samples of the rats. Results from previous studies show the protein content of the formulated diets to range from 15.75% in UMC to 17.24% in MMS. Significantly (p < 0.05) lower WBC, Hb, MCHC, total protein, albumin and globulin values were recorded for the rats fed a non-protein diet (NP). The serum AST level was 75.5, 71.2, 63.2, 51.0, 60.5 and 55.7, respectively, for rats on casein, rat pellet, MMS, UMS, MMC and UMC (list of abbreviations is shown in the appendix) diets. Alkaline phosphatase was significantly (p < 0.05) higher in soybean-based diets while cholesterol was lowest in rats fed the non-protein diet (NP). The value obtained for serum electrolyte concentration in the rats fed NP compared well with rats on other diets but, however, had a significantly (p < 0.05) higher serum sodium value. These results confirm that the experimental diets supported growth, as shown in a previous study, and had no harmful consequence.     

Intermediate density lipoprotein-apolipoprotein B turnover in rabbits fed semipurified diets containing casein or soy protein

The aim of this study was to investigate the underlying causes of elevated levels of intermediate density lipoprotein (IDL) in rabbits fed casein compared to soy protein in a cholesterol-free, semipurified diet. Kinetic studies were carried out in which homologous, radiolabelled IDL was injected into casein- and soy protein-fed animals after a period of 7 months on diet. Total plasma cholesterol and IDL cholesterol and protein were significantly higher in animals fed casein compared to those fed soy protein. The fractional catabolic rate of IDL-apolipoprotein B was significantly lower in casein-fed animals but the difference in mean values for the production rate did not reach statistical significance. The effect of feeding casein on IDL can be attributed to its reduced efficiency of removal from the plasma.     

Accumulation of cholesteryl esters and triglycerides in cultured macrophages incubated with plasma very low density lipoproteins from rats fed on casein or soybean protein diets containing moderate levels of cholesterol

Even when administered at a comparatively low level, dietary cholesterol produces significant changes in the properties of plasma lipoproteins in rats, particularly the d less than or equal to 1.006 g/ml fraction (VLDL). The occurrence of these changes is promoted by dietary casein. To test the hypothesis that these dietary-induced perturbations might include properties influencing lipoprotein-cell interactions of relevance to atherogenesis, cultured mouse peritoneal macrophages were incubated with VLDL isolated from male rats fed on diets containing either 0, 0.25 or 0.5% cholesterol with casein or soybean protein, respectively, as the sole source of protein. No increase in cholesteryl ester content, and a comparatively small rise in triglyceride content, was observed in macrophages incubated with VLDL from rats fed on cholesterol-free diets. In contrast, a significant and apparently saturable cellular accumulation of cholesteryl esters as well as triglycerides was produced by VLDL from cholesterol-fed rats. The curves showing cellular lipid accumulation versus VLDL-protein (or VLDL-cholesterol) content in the cell medium indicated different cellular affinity for VLDL from casein-fed rats in comparison with VLDL from soybean protein-fed rats. The apoprotein composition of VLDL differed between groups of rats fed on different types of dietary protein with higher proportions of apo C's in the casein-fed rats. In addition, cholesterol feeding resulted in increased proportions of apo A-I and apo A-IV in the plasma VLDL fraction.     

Bile acids do not regulate the intestinal mucosal cholesterol synthesis: studies in the chronic bile duct-ureter fistula rat model

Control male Wistar rats with intact bile circulation, animals with a bile duct-right ureter fistula, and bile duct-right ureter fistula rats fed taurocholic acid (5.5 mg/day) were maintained on a cholesterol-free pellet diet and pulse labeled subcutaneously with radioactive cholesterol. Bile acid feeding did not interfere with the synthesis of cholesterol by the intestinal mucosa or by the whole body in spite of markedly lowering the production of bile acids. Of the total fecal cholesterol mass in bile fistula animals roughly 25% originated from plasma filtration and 75% was ascribed to local mucosal cholesterol synthesis.