Soy Protein Group Research Articles

Effects of Soy Protein on Plasma Cholesterol and Bile Acid Excretion in Hamsters

The effect of dietary casein and soy protein on lipoprotein metabolism was compared in the Golden Syrian hamster (Mesocricetus auratus). Total plasma cholesterol was similar in animals fed either protein, but significant differences were seen in lipoprotein profile. In animals fed soy protein, cholesterol concentrations were lower in very-low-density lipoproteins (VLDL) but higher in low-density and high-density lipoproteins, compared with those fed casein. Significant differences were also seen depending on the nutritional state of the animals. In casein-fed hamsters, total plasma triacylglycerol and chylomicron + VLDL cholesterol and triacylglycerol were significantly higher when blood was collected during feeding, compared with animals that had been fasted overnight. By contrast, no significant change was seen in animals on the soy protein diet. This suggests that either intestinally derived lipoproteins are more rapidly cleared on the soy protein diet or that soy inhibits feeding-induced VLDL secretion. Fecal bile acid excretion was higher in the soy protein group, and there was a significant correlation between soy intake and bile acid excretion. Hepatic cholesterol decreased as the amount of soy protein consumed increased, suggesting that it is this pool of cholesterol that is used to replace the excreted bile acids. No significant difference was seen in plasma insulin or glucagon between hamsters fed the two proteins. Plasma triiodothyronine concentrations were, however, significantly higher and thyroxine concentrations lower in the soy protein-fed animals. This study shows specific effects of dietary proteins on plasma lipoprotein concentrations dependent on nutritional status of the animal.

97/03888 Reactivity of char from pyrolysis of birch wood

The importance of size and charge of carbohydrate moiety in tofu whey–carbohydrate conjugates, formed through Maillard-type glycosylation, was investigated. Tofu whey (TW) ultrafiltered fractions (UFTW > 3 kDa and UFTW < 3 kDa), acid-precipitated protein (APP), β-conglycinin (7S) or glycinin (11S) were covalently conjugated with carbohydrates (galactomannan (GM), okara polysaccharides, xyloglucan (XG), chitin and chitosan oligo), through naturally-occurring Maillard-type glycosylation at controlled temperature (60 °C), relative humidity (65%) and pH (7.0) for 7-days. The UFTW > 3 kDa fraction conjugated to polysaccharides or oligosaccharides showed improved emulsifying activity index (EAI) and emulsion stability (ES) (p < 0.05). The UFTW < 3 kDa, APP, 11S and 7S–oligosaccharide conjugates showed almost 3.0 times improvement in ES but no significant difference in EAI. In addition, UFTW < 3 kDa, APP, 7S, and 11S–chitosan oligo conjugates showed 5.0 times lower EAI and ES than those conjugates with XG or chitin oligo, due to electrostatic interaction between the negatively-charged groups of soy protein and positively-charged groups of chitosan oligo. Tofu whey fraction–carbohydrate glycoproteins showed both high and low water or oil-binding capacities, implying that different carbohydrates utilised in the preparation of glycoproteins possess different properties and mechanism in water or oil-binding capacity.

Short-Term Metabolic Responses Do Not Differ between Neonatal Piglets Fed Formulas Containing Hydrolyzed or Intact Soy Proteins

Hydrolyzed soy protein (SH) could be used as a protein source in formulas for infants with intolerance to cow's milk protein and may be preferable to intact soy protein (SI). However, metabolic responses to SH are poorly defined. Because of their partially hydrolyzed nature, nonphysiological elevations in either plasma amino acids or regulatory hormones may occur. Therefore, we evaluated effects of SH on plasma nutrient and pancreatic hormone (insulin, glucagon) concentrations. In Exeperiment 1, 24 newborn pigs were fitted with umbilical arterial and portal catheters, fed formula for 36 h and food deprived for 12 h. Pigs were then fed formula including either SH or SI with gludcose polymers or casein-whey protherins (CW) containing lactose, and serial blood samples were taken for 2 h postprandially. Peak portal exceeded peak arterial amino acid concentrations within each treatment, and peak amino acid concentrations in CW-fed pigs exceeded those of SH- and SI-fed pigs. However, only SH formula-fed piglets had higher postprandial portal minus arterial amino acid concentrations (P < 0.05) throughout Experiment 1, suggesting that SH was well digested and absorbed. In Experiment 2, arterial catheters were inserted in 24 piglets. Previous procedures were followed except dietary carbohydrate was standardized to glucose polymers for all three diets, and sampling was extended to 3 h. Overall, portal or arterial nutrient and hormone concentrations were not different in the SI and SH groups (P > 0.05), indicating that hydrolyzed soy protein did not cause abnormal plasma concentrations. In conclusion, hydrolyzed soy protein did not result in elevated nutrient concentrations or hormone responses compared with intact soy or cow's milk protein.

Antioxidant enzymes response to endurance exercise training and dietary proteins in rat skeletal muscle and liver.

This study was conducted to observe the effects of endurance exercise training on antioxidant enzyme activity in the liver and gastrocnemius muscle of rats being fed dietary casein and soy protein. The respective influences of dietary casein and soy protein on the activity of antioxidant enzymes were also compared. Thirty-nine male Wistar rats, aged 3 weeks, were randomly assigned to six groups: a normal protein control group, a normal protein endurance training group, a casein protein control group, a casein protein endurance training group, a soy protein control group, and a soy protein endurance training group. The endurance exercise training groups were adapted to a treadmill for 2 weeks prior to the date the rats were forced to run for 60 min at 25 m/min, 5 days/week for 12 weeks. We found that antioxidant enzyme activity in the gastrocnemius muscle was neither effected by the dietary proteins (casein and soy protein) nor by the above endurance exercise training load. However, hepatic Cu,Zn-SOD activity increased significantly for the dietary casein and soy protein diet groups as compared with the normal protein diet group (P < 0.01). Furthermore, significant increases both in hepatic Cu,Zn-SOD activity in the normal protein group and hepatic GSHpx activity in the casein and soy protein groups were observed when rats were loaded with 25 m/min of endurance exercise training (P < 0.01). These results suggest that, under the above experimental conditions, a casein or soy protein diet increase hepatic Cu,Zn-SOD activity, while endurance exercise training is effective in increasing hepatic Cu;Zn-SOD activity on a normal protein diet and in increasing hepatic GSHpx activity for cysteine and methionine deficient diets.

Soy and experimental cancer: animal studies.

Studies are reviewed that report consumption of soy protein diets inhibits the growth of various tumors in rats. The inhibitory effect has been attributed to the phytoestrogens (genistein and diadzein) or protein kinase inhibitor in soy protein products. Recent studies indicate that additional factors in soy protein products may also contribute to the inhibition of tumorigenesis, namely the deficiency of the essential amino acid methionine. Metastatic growth to the lungs of a primary rhabdomyosarcoma tumor was inhibited by feeding a soy protein diet. The effect was reversed by methionine fortification of the diet. Carcinogen-induced mammary tumor development was inhibited during the promotional phase in rats fed soy protein isolate diet and reversed with a methionine-supplemented diet. Additional studies demonstrated that after excision of the primary mammary tumor, growth of additional tumors was inhibited when the diet was changed from casein to soy protein isolate. Histopathologic evaluation of the mammary tumors revealed more benign fibroadenomas and lower-grade adenocarcinomas in the soy protein group. Before carcinogen administration (at 7 weeks of age), ornithine decarboxylase activity and polyamine concentrations in the rat mammary epithelium were significantly lower in the soy protein group. These data suggest an inhibitory effect on mammary epithelial growth in the soy-protein-fed group.

Qualitative and quantitative effects of dietary proteins on hyperlipidemia and proteinuria in nephritic rats

Effects of qualitative and quantitative differences in dietary poteins on hyperlipidemia and proteinuria were studied in rats with nephrotoxic serum nephritis. Dietary proteins examined were milk casein, whole egg protein, soy protein isolate and wheat gluten. Rats were maintained on experimental diets for 14 days after an injection of nephrotoxic serum to induce nephritis. In the qualitative study, almost the same extent of growth and urinary protein excretion was observed in a 20% casein (20C), egg protein (20E) and a soy protein (20S) group. Growth and protein excretion of a 20% gluten (20G) group were suppressed compared with that of the other three groups. The serum lipid levels were highest in the 20E group and lowest in the 20G group. In the quantitative study, 8.5% protein diets, in general, ameliorated hyper lipidemia and proteinuria but retarded the growth of rats compared with the corresponding 20% protein diets, except for an 8.5% egg protein diet that did not suppress the growth. These results suggest that amino acid-balanced low protein diets improve hyperlipidemia and proteinuria without growth retardation in nephritic rats.

Effect of soy protein diet versus standard low fat, low cholesterol diet on lipid and lipoprotein levels in children with familial or polygenic hypercholesterolemia

The effect on serum lipid and lipoprotein levels of a standard low fat, low cholesterol diet was compared with that of a soy protein-substituted low fat, low cholesterol diet in 23 children with familial or polygenic hypercholesterolemia: 12 boys and 11 girls (mean age, 9.3 +/- 4.5 years) were included in this outpatient program. Group 1 received the soy protein diet for 8 weeks; group 2 received the low fat, low cholesterol diet. After an interruption of 8 weeks, each group was placed on the alternate regimen. Fasting blood samples were collected at the beginning of each dietary period. During the soy protein diet, the levels of total cholesterol decreased by 16% in group 1 and 18% in group 2, and low-density lipoprotein cholesterol (LDL-C) levels decreased about 22% in group 1 and 25% in group 2. During the standard low fat, low cholesterol diet, total cholesterol and LDL-C levels were reduced by 8% and 7% in group 1 and by 12% and 13%, respectively, in group 2. The effect on LDL-C was significantly greater (p < 0.05) in the soy protein group than in the low fat, low cholesterol group. We conclude that a diet substituting soy protein for animal protein has a more beneficial short-term effect on total cholesterol and LDL-C levels in children with hypercholesterolemia than a standard low fat diet.

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.

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 μCi [ 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.

54Mn absorption and excretion in rats fed soy protein and casein diets.

Rats were fed diets containing either soy protein or casein and different levels of manganese, methionine, phytic acid, or arginine for 7 days and then fed test meals labeled with 2 microCi of 54Mn after an overnight fast. Retention of 54Mn in each rat was measured every other day for 21 days using a whole-body counter. Liver manganese was higher (P less than 0.0001) in soy protein-fed rats (8.8 micrograms/g) than in casein-fed rats (5.2 micrograms/g); manganese superoxide dismutase activity also was higher in soy protein-fed rats than in casein-fed rats (P less than 0.01). There was a significant interaction between manganese and protein which affected manganese absorption and biologic half-life of 54Mn. In a second experiment, rats fed soy protein-test meals retained more 54Mn (P less than 0.001) than casein-fed rats. Liver manganese (8.3 micrograms/g) in the soy protein group was also higher than that (5.7 micrograms/g) in the casein group (P less than 0.0001), but manganese superoxide dismutase activity was unaffected by protein. Supplementation with methionine increased 54Mn retention from both soy and casein diets (P less than 0.06); activity of manganese superoxide dismutase increased (P less than 0.05) but liver manganese did not change. The addition of arginine to casein diets had little effect on manganese bioavailability. Phytic acid affected neither manganese absorption nor biologic half-life in two experiments, but it depressed liver manganese in one experiment. These results suggest that neither arginine nor phytic acid was the component in soy protein which made manganese more available from soy protein diets than casein diets.

Hepatic Cysteine Dioxygenase Activity and Sulfur Amino Acid Metabolism in Rats: Possible Indicators in the Evaluation of Protein Quality

Experiments were carried out to examine the possibility that the sulfur amino acid metabolism of rats may be an indicator of the nutritional value of dietary protein. Rats were fed diets containing 8, 16 or 24% of gluten, soy protein or casein for 3 wk. Hepatic cysteine dioxygenase activity, hepatic concentration of glutathione, cysteine and taurine and urinary taurine were examined. In addition, the sulfur amino acid metabolism of rats fed these diets fortified with the appropriate first limiting amino acid for 7 d was also examined. High urinary taurine excretion was observed in the three gluten groups, whereas very low urinary taurine excretion was observed with up to 24% soy protein or up to 16% casein. The hepatic hepatic cysteine dioxygenase activities of the gluten diet groups were higher than those of corresponding soy protein or casein diet groups, except that of rats fed the 24% casein diet. The hepatic concentrations of both glutathione and cysteine in gluten diet groups were also higher than those of corresponding soy protein or casein diet groups, except 24% soy protein and 16 and 24% casein diet groups. In rats fed the casein or soy protein diets urinary taurine excretion and hepatic cysteine dioxygenase activity increased with increasing methionine supplementation, the first limiting amino acid. Conversely, in rats fed the gluten diet both urinary taurine excretion and hepatic cysteine dioxygenase activity decreased with increasing lysine supplementation, the first limiting amino acid. These findings suggest that urinary taurine excretion and hepatic cysteine dioxygenase activity may be useful as sensitive indicators of the nutritional value of dietary protein.

Short- and long-term effects of hypocaloric diets containing proteins of different sources on plasma lipids and apoproteins of obese subjects.

The influence of caloric restriction on lipid profile is controversial. This study was designed to evaluate the influence of dietary proteins from different sources on lipoprotein levels in obese subjects during a period of very low-caloric diet followed by 60 days of hypocaloric diet. The subjects were 24 obese patients aged 25-42 of at least 50% above ideal weight. The patients were separated into two groups and received for 15 days 375 kcal/day on the assumption that commercial textured preparations contained the same amount of proteins, respectively, as casein (group A) or soy protein (group B). Then the very low-caloric diet of the two groups was integrated with 425 kcal/day for 60 days. Body weight reduction was equivalent in the two groups. Total plasma cholesterol decreased significantly in both groups after the two periods of diet, but the percent variations were always significantly higher in the group B than in A. Total plasma triglycerides reduced significantly only in the group B. Very low-density lipoprotein (VLDL) and low-density lipoprotein (LDL) cholesterol behaved as total cholesterol in the two groups. High-density lipoprotein (HDL) cholesterol diminished significantly only after the 15 days of very low-caloric diet in group B, while it decreased throughout the diet in group A. The decrease of HDL cholesterol was mainly due to the HDL2 subfraction. The results of our study show that the substitution of soy protein for casein can be of benefit in those patients who need a long-term hypocaloric diet.

Effects of postnatal protein undernutrition on myelination in rat brain

1.1. Pups were subjected, from birth, to protein undernutrition by feeding the lactating dams 8% casein (CS) or 8% soy protein (SP) diet up to weaning; the weanlings were fed the same diets until 6 weeks of age.2.2. At 3 and 6 weeks of age, myelin was isolated from the brains and characterized. The quantities of myelin and its content of cholesterol, galactolipids and phospholipids, were significantly depressed in the 8% CS and 8% SP groups but not when soy protein was fed at the same level as casein (25%) in the control.3.3. Furthermore, the severity of the deficits in myelination showed a differential pattern depending on the type of dietary protein fed.4.4. At weaning, the deficits with the 8% SP diet were 1.5–2.0-times greater than with the corresponding casein diet.5.5. A more pronounced retardation in the initiation, progression and capacity of myelination in postnatal soy protein undernutrition was indicated.

Regression of casein and cholesterol-induced hypercholesterolaemia in rabbits.

Hypercholesterolaemia was induced in rabbits by feeding semipurified diets containing soy protein plus cholesterol (0.8 g/kg) or casein for four weeks. Subsequently for a period of six weeks, some of the rabbits were transferred to diets containing soy protein while others continued to receive the hypercholesterolaemic diets to which was added a mixture of amino acids (g/kg feed; glycine, 3.9; arginine, 6.9 and alanine, 1.6). Such additions increased the concentration of these amino acids in the casein diet to that in the hypocholesterolaemic soy protein diet. The cholesterol levels in the serum of the rabbits transferred to the soy protein diets declined rapidly, becoming significantly different from animals remaining on the hypercholesterolaemic diets after only three days. Serum cholesterol levels comparable to those in rabbits fed soy protein throughout the entire experiment were reached after about two weeks. The addition of the amino acids tended to reduce the concentration of cholesterol in the serum of the rabbits made hypercholesterolaemic by feeding the diets containing either casein or cholesterol. However, the effect reached significance only with the diet containing casein to which amino acids were added and then only at one time point. Six weeks after the cholesterol-fed animals were transferred to the cholesterol-free soy protein diet or to the diet containing the additional amino acids, apo E disappeared from the IDL1 (1.006 less than d less than 1.012 g/ml) and IDL2 (1.012 less than d less than 1.019 g/ml) fractions, but not from the VLDL fraction. Both with the cholesterol-free soy protein diet and the cholesterol diet fortified with amino acids, cholesterol in the VLDL fraction was reduced to values seen in animals fed the soy protein diet throughout the entire experimental period. The amount of cholesterol in the IDL and LDL fractions was decreased only in the soy protein group. Replacement of casein by soy protein, or the addition of amino acids to the casein diet did not induce the disappearance of apo E from the IDL or VLDL fractions. Only the soy protein diet lowered the amount of cholesterol in the VLDL and LDL fractions appreciably. It is concluded that the amount of apo E present in both IDL and VLDL does not invariably correlate with the level of serum cholesterol in rabbits. This study also indicates that the hypercholesterolaemic nature of casein resides only partially in the fact that it contains relatively low proportions of glycine, alanine and arginine compared with soy protein.

Effects of a soy protein product on serum and tissue cholesterol concentratins in swine fed high-fat, high-cholesterol diets

Hypocholesterolemic effect of a soy protein product was studied in swine fed a high-fat, high-cholesterol diet. In the first experiment, a group of swine were fed 42% butter (by calories) and 1055 mg cholesterol daily, with casein as the source for protein, for 6 weeks and this diet resulted in moderately high serum cholesterol concentrations (219 ± 33 mg/dl). Another group fed the same diet except with soy protein product as the protein source instead of casein showed virtual normocholesterolemia at the end (107 ± 3 mg/dl). Cholesterol balance was studied under non-steady state conditions using methods designed for this purpose. Reflecting the serum cholesterol concentration, the total body cholesterol concentration (excluding CNS) was also significantly lower in soy protein group. However, parameters of cholesterol balance, such as fecal neutral and acidic steroid excretions, dietary cholesterol absorption, and whole body cholesterol synthesis were studied and no differences were demonstrated between the casein- and soy protein-fed swine. The experiment was repeated and in Experiment II virtually the same results were obtained. When swine were given the same high-fat, high-cholesterol diets with 1 2 casein + 1 2 soy protein or casein + soy protein, hypocholesterolemic effects were also observed. Therefore, such action is probably caused principally by soy protein per se rather than simply by replacement of casein by soy protein. Addition of dl-methionine to soy protein containing diet did not alter the hypocholesterolemic effect of soy protein indicating that the effect was not the result of methionine deficiency. In conclusion, we can state that the hypocholesterolemic action of soy protein was clearly demonstrated in swine fed a high-fat, high-cholesterol diet, but that the mechanism of action is yet to be established.

Differential Nitrogen Retention from Casein, Lactalbumin, and Soy Protein, and Hydrolysates Therefrom

Summary The various data illustrating different methods for the biological evaluation of the protein lead, generally speaking, to the same conclusions. The evidence clearly shows the superiority of lactalbumin over casein and the superiority of both casein and lactalbumin over soy protein. If a relative value of 100 was assigned to the lactalbumin, the value for the casein would be about 80 and that of the soy protein between 50 and 60. These general relationships have been indicated by published data from time to time, although the magnitude of the differences have been subject to variations depending upon the particular methods used. Reference has been made to the linear relationship between nitrogen balance and absorbed nitrogen wherein variations in the slopes of the curves are of value as a means for determining the relative or absolute merits of the test materials. Such evidence shows that in each instance the original protein is slightly superior to its hydrolysate in respect to maintenance of a positive nitrogen balance. This relationship, however, is not consistently shown by the calculated biological values (table 1).The relatively greater difference between the iso-electric albumin and its hydrolysate may be accounted for by the intermediate step of peptization before hydrolysis. The difference between the peptized lactalbumin and the hydrolysate prepared direct therefrom is not of substantial magnitude. Two significant deductions may be drawn from the data as a whole. First, appropriate preparation of protein hydrolysates may offer a means of extracting unavailable or indigestible protein from sources not recognized as suitable food products. Second, the mere stipulation of a given percentage of protein in foods or feed stuffs is inadequate in describing their protein value. For instance, in using the nitrogen balance data as a basis of interpretation the soy protein has only about 50 per cent the value of the lactalbumin and about 60 per cent the value of casein; the other data are in substantial agreement. From the standpoint of protein conservation and food economy it is seemingly apparent that as a particular protein more nearly approaches the ideal a commensurate reduction in the amount of dietary protein could be made. The physiological aspects of the lower protein intake may also be of importance from the standpoint of health because the data indicate that a large proportion of the nitrogen absorbed from inferior protein is excreted without commensurately contributing to physiological functions. The average survival period of the groups of animals used in these investigations when furnished the nitrogen-free diet following the test period tends to indicate a significant effect of the previous protein intake. The average survival time for the lactalbumin group was about 30 per cent longer than for the soy protein group, and the survival time for the casein group was about 24 per cent longer than for the soy protein group. One may presume that the variations observed are due to an imbalance or deficiency of amino acids, or possibly to an absence of physiologically important linkages in the inferior protein molecule. If evidence should clearly disclose that the former condition is the cause of the differences, the fortification and enhancement of a deficient protein by appropriate synthetic amino acids in proper balance should prove to be of importance from the standpoint of health and economy and conservation of natural food protein.