• Preventive Nutrition and Food Science
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• v.7 no.3
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• pp.278-281
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• 2002

The objective of the current study was to determine the influences of dietary proteins and methionine on plasma lipid concentrations. Thirty growing male Sprague-Dawley rats were fed diets similar in all respects except that dietary protein was from either casein, soy protein isolate, or soy protein isolate supplemented with L-methionine (0.24 %). The animals were fed experimental diets ad libitum for nine weeks. Plasma total-cholesterol concentrations were unaffected by the protein source or methionine supplementation. Plasma triglyceride concentrations were lower in rats of methionine supplemented soy protein diets (76 mg/dL) than in the rats fed casein or soy diet (120 mg/dL, 109 mg/dL, respectively). These results indicate that soy protein reduces plasma triglycerides relative to casein in rats fed cholesterol free diets, and that methionine-supplemented soy diets decrease plasma triglyceride concentrations more than soy protein alone.

• Journal of Nutrition and Health
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• v.27 no.1
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• pp.3-11
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• 1994

This study was carried out to examine how dietary protein and calcium levels in rats fed fat-enriched diet affect the total lipid and cholesterol contents of blood and tissues. Male Sprauge-Dawley rats weighing approximately 200g were fed six purified diets which contained 18%(w/w) beef tallow, 1% (w/w) cholesterol, two source of protein, casein or isolated soy protein (ISP) and three levels of dietary calcium, 0.1%, 0.4% and 1.0%, first, for four weeks, and second, for eight weeks. The contents of the total lipid, cholesterol and triglyceride in blood, liver, heart and feces were determined. After four weeks feeding serum lipid and cholesterol concentrations significantly decreased in rats fed 1.0% (w/w) level calcium, regardless of dietrary protein sources. After eight weeks, these concentrations were significantly lower in the rats fed soy protein than in casein-fed rats. As dietary calcium level increased serum and tissue lipid and cholesterol contents were decreased and fecal lipid excretion increased. It is concluded that hypolipidemic and/or hypocholesterolemic effects of soy protein and calcium were partly due to decrease in lipid absorption.

• Journal of Nutrition and Health
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• v.15 no.2
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• pp.119-128
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• 1982

The effect of dietary protein on growth and lipid levels of plasma and liver was studied in weanling male rats fed diets differing protein sources and amino acid balance. Rats were devided into 9 experimental diets which were grouped into 3 categories ; 1) Simple protein category includes gluten-, soy protein isolate-, and casein-containing diet groups, 2) Supplemented category includes casein supplemented with methionine, soy protein isolate supplemented with methionine, and gluten supplemented with lysine and methionine, 3) Mixed protein category includes diet groups containing gluten (2/3), casein (1/3), soy protein isolate (2/3) and casein (1/3), and casein (1/3), soy protein isolate (1/3) and gluten (1/3). The experimental diets composed of 15% protein, 65.8% carbohydrate, 10% fat and 1% cholesterol. The body wt. gain and P.E.R. were greater in rats of supplemented and mixed protein groups than simple protein groups. No statistical differences were found in plasma cholesterol among gluten, soy protein isolate and casein groups. Consumption of diets supplemented with limiting amino acid to gluten or soy protein isolate reduced the plasma cholesterol level by 23.2% and 34.2% respectively. However there was no difference between casein and the supplemented casein groups. The mixed protein groups shows relatively high plasma cholesterol concentration and low liver cholesterol levels. On the other hand gluten group showed low plasma cholesterol and high liver cholesterol levels, which means body cholesterol pool may not have been changed by the dietary protein. Feeding soy protein meal and the supplemented soy protein isolate resulted in lower plasma cholesterol, plasma triglycerides, liver cholesterol and liver triglycerides levels. This hypolipidemic effect is considered to see unique to soy protein isolate. Rats in gluten and the supplemented gluten groups showed lower plasma protein levels and a tendency of fatty liver.

• Journal of Nutrition and Health
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• v.37 no.2
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• pp.100-107
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• 2004

This study was performed to evaluate the effect of dietary protein source and sulfur amino acid content on bone metabolism in ra. Thirty male rats (body weight 145$\pm$2g) were divided into three groups. The rats in the first group were fed on casein 20% diet as animal protein source and those in the second group were fed on soy 20% diet as plant protein source. Sulfur amino acid ratio of these group was 1.07:1. The rats in the third group were fed on soy 20% diet and the sulfur amino acid were supplemented with the amount contained as much in the soy 20% diet. All rats were fed on experimental diet and deionized water ad libitum for 9 weeks, The total body, spine, femur bone mineral density and bone mineral content were measured using Dual Energy X-ray Absorptiometry Calcium, phosphate, pyridinoline, creatinine in urine and calcium, phosphate, alkaline phosphatase, osteocalcin in serum were measured. During the experimental period, plant protein (soy protein) group had a lower urinary Ca excretion, urine pyridinoline ＆ crosslinks value and had a higher Ca efficiency in total bone and femur bone mineral density than animal protein (casein) group. There were no significant differences in serum calcium, phosphate, alkaline phosphatase and osteocalcin among the three groups of the rats. The findings from this study demonstrated that plant protein (soy protein) is beneficial of bone mineral density because it had a higher Ca efficiency in total bone and femur bone mineral density than animal protein (casein). However, the supplementation of sulfur amino acid on soy results were consistent with prior studies that dietary sulfur amino acid load had a negative effect on calcium balance. The rats fed sulfur amino acid supplementation diet increased urinary calcium excretion and decreased calcium efficiency for total and femur mineral density. Therefore, dietary protein source and sulfur amino acid content influence bone metabolism. (Korean J Nutrition 37(2): 100-107, 2004)

• Korean Journal of Rural Living Science
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• v.6 no.1
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• pp.31-39
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• 1995

This study was performed to observe how soy protein and calcium in rats fed unsaturated fat-enriched diet affect the total lipid and cholesterol contents of blood and tissues male Sprague-Dawley rats weighing approximately 220g were fed four purified diets which contained 18% (w/w) corn oil, 1% (w/w) cholesterol, two sources of protein : casein or isolated soy protein (ISP) and two levels of dietary calcium : 0.1% or 1.0%, first for four weeks (Expt. 1) and second for eight weeks (Expt. 2). The contents of total lipid, cholesterol and triglyceride in blood, liver, heart and feces were determined. After four weeks feeding, the serum lipid and cholesterol concentration was not significantly different among the groups. After eight weeks feeding, these concentrations were significantly lower in ISP-High calcium group. The serum lipid concentration was influenced by dietary protein sources and calcium levels. These results indicated that the hypolipidemic effects of soy protein and high calcium intake were partly due to decrease in lipid absorption and these effects were not detected at 4 weeks feeding but 8 weeks feeding.

• Nutritional Sciences
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• v.9 no.4
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• pp.240-247
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• 2006

In this study we investigated the neuroprotective, antioxidative, and hypocholestrolemic effects of dietary soy protein and soy isoflavone in a rat focal brain ischemia model. Weaning Sprague-Dawley rats were fed a 20% casein-based diet (CA), 20% soy protein-based diet (SP), or 0.2% soy isoflavones-supplemented diet (ISO) for 6 weeks. The cortical infarction volume of the ISO group was significantly lower than that of the SP group. The thiobarbituric acid reactive substances (TBARS) were considerably lower in the ISO group than the CA group. Glutatbione peroxidase activities of the SP group were notably higher than those of the CA group. Acetylcholinesterase (AchE) activities of the SP group were significantly decreased compared to the CA group. LDL cholesterol levels and LDL/HDL ratios of the ISO group were lower than those of the CA and SP groups. Our results collectively suggest that soy isoflavones may contribute to neuroprotection by reducing the TBARS and serum LDL/HDL ratio, whereas soy protein may be associated with the regulation of cognitive functions by modulating AchE activity.

• Korean Journal of Community Nutrition
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• v.4 no.2
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• pp.239-247
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• 1999

Six-week-old Sprague Dawley rats were fed the diets of 20% casein or soy protein. Two weeks after the feeding, hepatocellular chemical carcinogenesis was initiated by diethylnitrosamine(DEN), and promoted by the diet containing 0.01% 2-acetylamino-fluorene(AAF) and two-thirds partial hepatectomy(PH). The animals were sacrificed at 8 weeks after the DEN injection. The area of placetal glutathione S-trnasferase(GST-P) positive foci, the activities of several enzymes in cellualr antioxidant enzyme systems and glucose 6-phosphatase were determined to investigate the mechanism of the anticarcinogenic effect by the dietary proteins. In another set of experiments, the drinking water of rats fed casein was supplemented with 1.5% inositol hexaphosphate(InsP6) to elucidate whether it has the comparable anticancer action of soy protein. The area and number of GST-P positive foci in the soy protein group were significantly(p<0.05) lower than those inthe casein group. The livers of rats fed casein showed moderate fattydegeneration and larger hyperplastic nodules than those of rats fed soy protein. In another set of experiments, the area and number of GST-P positive foci in the rats fed casein supplemented with InsP6 were not significantly different from those in the rats fed casein or soy protein. The lipid peroxidation of rats fed different protein sources showed no significant difference. Glutathione S-transferase(GST) activities were increased significantly(p<0.05) by carcinogen treatment in all dietary groups. Glucose 6-phosphatase(G6Pase) activities were decreased by carcinogen treatment, and hence showed a reverse relationship(r=-0.695, p<0.01) to the GST-P positive foci. Therefore, the activities in the rats fed casein were lower than those in the rats fed soy protein. These results suggest that the soy protein seems to be more anti-carcinogenic than casein by decreasing the preneoplastic lesion and by increasing the membrane stability but inositol hexaphosphate, a component of soy protein, may not be protective against hepatocarcinogenesis.

• Journal of the Korean Applied Science and Technology
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• v.3 no.1
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• pp.23-31
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• 1986

Several authors reported that vegetable proteins cause to decrease serum cholesterol and reported the effect of limiting amino acid balance in dietary protein on the blood component. This study was designed to observe growth rate and blood component in 1% cholesterol-fed male rats intake pure isolated soy proteins and methionine for 4 weeks. The diets were supplemented with either 20% casein or isolated soy protein as dietary protein sources and methionine as limiting amino acid of isolated soy protein and casein protein. The results were as follows; 1) The body weight gain was the greatest in casein groups. 2) Serum total cholesterol concentration was significantly increased by casein groups and slightly decreased by isolated soy protein groups. 3) Serum HDL-cholesterol concentration was significantly increased by isolated soy protein groups than control group. 4) Serum total lipid and triglyceride concentrations were significantly decreased by isolated soy protein groups than control group. 5) Serum glucose concentration was significantly increased by isolated soy protein plus 0.8% methionine than control group. 6) Serum total protein and albumin concentrations were significantly increased by all experimental diets groups than control group. Especially, casein groups were the most increased in all experimental diets groups.

• Journal of Nutrition and Health
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• v.27 no.9
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• pp.883-891
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• 1994

The number of diabetics in Korea is about 3 to 5 percent of the population, and the incidence is increasing yearly due to changes of life style and food intake. Diet is a key element in the management of diabetes, yet the appropriate diet for diabetes remains controversial. We have recently shown that a diet rich in protein of animal origin(casein) seems beneficial to controling plasma glucose and lipids in streptozotocin-induced diabetic rats. It therefore seemed desirable to find out whether the beneficial effect of high casein diet in experimental diabetes could also be reproduced with a vegetable source of protein(soy). The purpose of this study is to compare these results with the results of our previous study. In the present study, non-diabetic and streptozotocin-induced diabetic rats were studied in order to examine the effects of altering the level(20% vs 60%) of dietary soy protein on blood glucose, lipids, and hormones. Results of the present study showed that a high soy protein diet decreased triglyceride concentration in diabetic rats. However, diabetic rats fed a high soy protein diet were not hypocholesterolemic compared to rats fed a control diet. Moreover, diabetic rats fed a high soy protein diet had significantly increased plasma glucose concentration compared to rats fed a control diet. This study was not able to discern a specific effect of dietary protein level on insulin, glucagon, or insulin/glucagon ratio. Except for the hypotriglyceridemic effect, the results were not similar to the findings of our previous study which showed a beneficial effect on streptozotocin-induced diabetic rats fed a high casein diet.

• Journal of Nutrition and Health
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• v.27 no.1
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• pp.90-99
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• 1994

This study was carried out to examine how dietary protein and calcium levels in rats fed fat-enriched diet affect the total lipid and cholesterol contents of blood and tissues. Male Sprauge-Dawley rats weighing approximately 200g were fed six purified diets which contained 18%(w/w) beef tallow, 1% (w/w) cholesterol, two source of protein, casein or isolated soy protein (ISP) and three levels of dietary calcium, 0.1%, 0.4% and 1.0%, first, for four weeks, and second, for eight weeks. The contents of the total lipid, cholesterol and triglyceride in blood, liver, heart and feces were determined. After four weeks feeding serum lipid and cholesterol concentrations significantly decreased in rats fed 1.0% (w/w) level calcium, regardless of dietrary protein sources. After eight weeks, these concentrations were significantly lower in the rats fed soy protein than in casein-fed rats. As dietary calcium level increased serum and tissue lipid and cholesterol contents were decreased and fecal lipid excretion increased. It is concluded that hypolipidemic and/or hypocholesterolemic effects of soy protein and calcium were partly due to decrease in lipid absorption.