Pancreatic response to long-term feeding of soy protein isolate, casein or egg white in rats

Rats were fed purified diets which provided 24% protein from casein (C), soy protein isolate (SPI), or egg white (EW) for 18 mo. Groups of rats were killed at 3, 6, 12 and 18 mo; the pancreata were removed and examined histologically for occurrence of atypical nodules. The weight, protein, DNA, trypsin and chymotrypsin concentrations of the pancreas at each period were measured. Over the entire experimental period, body weight did not differ among groups. Pancreatic weight, protein and trypsin activity were highest in the EW group, followed by the SPI group, and lowest in the C group. Chymotrypsin activity was significantly higher in the EW and SPI groups than the C group. DNA content did not differ significantly among groups over the entire experimental period, although it was elevated in the SPI or EW groups compared to the C groups at some of the time periods. Only one microscopic nodule was observed in all of the animals; it was found at 3 mo in the pancreas from an animal fed EW. Overall, the results suggest that the elevation in enzyme activity and pancreatic weight associated with long-term consumption of EW and SPI did not result in development of pancreatic lesions in rats.     

不同来源的蛋白质对大鼠血脂水平的影响

目的研究雄性大鼠在长期摄入不同来源和含量的蛋白质饲料后,其血脂水平及各血脂比值的变化。方法将断乳雄性大鼠按体重随机分为4组(n=15),分别给予牛奶粉(HM组和LM组)或大豆粉/蛋清粉(HS组和LS组)为蛋白质来源的饲料(每种饲料中总蛋白质含量分别为18%和9%),持续喂养20周后,检测各组大鼠血清中血脂水平,并计算各类血脂的比值。结果在各实验组中,HM组大鼠血清总胆固醇(TC)和高密度脂蛋白胆固醇(HDL-C)水平最高(P<0.05),TC/HDL-C比值最低(P<0.05);HS组大鼠甘油三酯(TG)水平最低(P<0.05)。HS与HM组的TG/HDL-C比值低于LS与LM组(P<0.05)。LS与HS组低密度脂蛋白胆固醇(LDL-C)水平和LDL-C/HDL-C比值均低于LM与HM组(P<0.05)。结论给予高剂量大豆粉来源蛋白质,可以显著降低大鼠的TG水平;若长期给予高剂量牛奶粉作为蛋白质来源,可明显升高大鼠血清胆固醇总体水平。     

Intestinal zinc and carboxypeptidase A and B activity in response to consumption of test meals containing various proteins by rats

Rats were fed test meals containing 23% protein as casein (C), soy protein isolate (SPI) or egg white (EW) to assess effects of dietary protein sources on te amount of zinc and carboxypeptidase (CP, CPA, CPB) activity in the small intestinal contents. Groups of six rats each were killed at 1, 2.5 and 5 h postprandial and six rats fasted for 19 h served as a 0 time control. Consumption of a test meal increased the weight of small intestinal contents at 1 and 2.5 h compared with unfed animals and in a similar manner for all three protein sources. However, at various times during the postprandial period differences in the level of zinc and CP activity within the small intestinal contents among the three dietary protein sources were observed. Both the SPI and EW groups had significantly higher levels of CPA and CPB activity at 1 h postprandial than the C group. Only in the SPI group was the intestinal level of zinc increased at 1 and 2.5 h compared with the unfed group. At 1 and 2.5 h postprandial intestinal zinc was significantly higher in the SPI group than in the C and EW groups. The results indicate that the disappearance of zinc from the intestine is delayed in rats fed SPI, probably because of the presence of phytate.     

Comparative effect of casein and soybean protein isolate on body fat accumulation in adult rats.

The effect of dietary protein on the body fat accumulation was studied in rats. Adult rats weighing about 300 g were fed 21% protein (casein or soybean protein isolate) and 5% oil diets by pair-feeding for 65 days in Experiment 1. In Experiment 2, only protein and oil contents were changed, 25 and 10%, respectively. Final body weights of the two dietary groups were similar in both experiments, especially in Experiment 2. Total body fat was slightly lower in the soybean protein diet group than in the casein diet group in Experiment 2, only when it was expressed as the percentage against body weight. However, intra-abdominal fat was significantly lower in the soybean protein diet groups than in the casein diet groups in both experiments. Serum lipid levels were greatly lower in the soybean protein diet group than in the casein diet group in Experiment 2 (the data were not available in Experiment 1). The results suggest that dietary soybean protein has the effect to lower the intra-abdominal fat accumulation as compared with casein.     

Effects of feeding oyster,Crassostrea gigas,on serum and liver lipid levels in rats

The effects of feeding dietary and defatted oyster meat on lipid metabolism were investigated in rats by comparing measurements with those of casein and soybean protein. In the first experiment, male rats were fed 0.1% and 1% cholesterol-supplemented diets containing casein, oyster or soybean protein under the same dietary level of protein (20%). The concentrations of serum and liver cholesterol in the oyster group were significantly lower than those in the casein group for both the 0.1% and 1% cholesterol-supplemented diets. The cholesterol-lowering effect of oyster meat was more predominant than that of soybean protein. Feeding oyster meat significantly decreased the serum triglyceride concentration as compared to feeding casein for the 0.1% cholesterol-supplemented diets, and it reduced hepatic triglyceride concentration in both groups fed the 0.1% and 1% cholesterol-supplemented diets. The excretion of fecal total steroids was higher in the rats fed oyster meat than those fed casein or soybean protein for both the 0.1% and 1% cholesterol-supplemented diets. In the second experiment, the effects of defatted oyster on lipid metabolism were compared with casein and soybean protein in diets supplemented with cholesterol. The serum cholesterol concentration in the defatted oyster group was comparable to that in the other two groups, but the ratio of high-density lipoprotein-cholesterol to total cholesterol was higher in the defatted oyster group. The feeding of defatted oyster induced a lower liver cholesterol concentration as compared to casein and soybean protein. Serum and liver triglyceride levels were lower in the defatted oyster group than in the casein group. Defatted oyster accelerated the fecal excretion of both neutral and acidic steroids as compared to casein. Our results suggest that the feeding of oysters exerts a more potent hypolipidemic activity than soybean protein, and the effect may be ascribed to both lipid and non-lipid fractions in oyster.     

Interaction of dietary protein differing in sulfur amino acid content and pectin on bile acid conjugation in immature and mature rats

Rapidly growing immature (4-wk-old) and slowly growing mature (15-wk-old) rats were fed fiber-free or 10 g/100 g pectin diets containing various proteins differing in the sulfur amino acid content for 30-32 d. Soybean protein, casein, whole egg protein and egg albumen were used at the nitrogen level of 2.7 g/100 g diet. These experimental diets contained 0.354, 0.540, 0.945 and 1.22 g sulfur amino acids/100 g, respectively. In the rats fed fiber-free diets, a substantial quantity of glycine-conjugated bile acids was detected in the bile of immature rats fed soybean protein and casein (73 and 25% of total bile acids, respectively), but not in the other groups (less than 13%). Dietary pectin increased bile acid excretion both in immature (48-77%) and mature (34-114%) rats irrespective of the protein source, except in immature rats fed egg albumen and mature rats fed whole egg protein. Because a pectin-dependent increase in bile acid excretion was essentially attributed to the increase in glycine-conjugates, this dietary fiber significantly increased the ratio of glycine-conjugates to taurine-conjugates (2.4- to 6.5-fold). This increase was accompanied by a 40-50% decrease in the concentration of liver taurine, except in immature rats fed soybean protein and egg albumen. However, there was no consistent relationship between the extent of taurine conjugation and the activity of liver cysteine dioxygenase, one of the rate-limiting enzymes in taurine synthesis.     

三大营养素组成与家兔动脉粥样硬化关系研究

成年雄性大耳白兔30只,分为5组:对照组(适宜量组)、高酪蛋白组(蛋白质占总能量25％)、高大豆蛋白组(蛋白质占总能量25％)、高脂肪组(脂肪占总能量40％)和低脂肪组(脂肪占总能量16％),饲养80天。观察不同饲料组成对家兔主功脉组织形态、血脂水平、组织中总脂含量与脂肪酸组成和体重等的影响。结果表明,主动脉粥样硬化改变,对照组少而轻,其次是高酪蛋白组和低脂肪组,高脂肪组和高大豆蛋白组病变多且重。血清TC、TG、和LDL-C高脂肪组和高酪蛋白组(除TG外)均高于对照组,高大豆蛋白组和低脂肪组(除TG外)均低于对照组,HDL-C除低脂肪组外,各组相似。主动脉中脂肪含量受饲料影响最大,实验各组均高于对照组,且P/S值也小,对心肌影响较小,且P/S值均在1.12以上。说明饲料中三大营养素组成中不但量、而且动、植比也影响主动脉粥样硬化改变的程度。     

大豆蛋白和高钙摄入对高血胆固醇模型大鼠血脂水平的影响

目的探讨膳食大豆蛋白和/或高钙摄入对高血胆固醇模型大鼠血浆胆固醇及有关血脂指标的影响.方法用含5%猪油、1%胆固醇和0.25%胆碱的高脂饲料喂饲健康Wistar雌性大鼠,经14d诱发高血胆固醇以后,测血浆总胆固醇(TC),总甘油三酯(TG),高密度脂蛋白胆固醇(HDL-C)和载脂蛋白B(ApoB100)的浓度.然后,按体重和血浆胆固醇浓度将动物均衡分为4组,以2×2析因设计,分别喂饲含有酪蛋白和大豆分离蛋白及正常钙(0.59%)和高钙水平(1.12%)的纯合成高脂饲料.经21d喂养后,采血,测定指标同前.实验结果用SPSS统计软件进行方差分析.结果经14d诱导高血脂后,实验模型大鼠的TC水平为(4.10±1.11)mmol/L(n=24),而喂饲正常饲料的阴性对照鼠仅为(1.92±0.28)mmol/L(n=8),升高了2.14倍.又经21d喂饲含有处理因素的饲料后,酪蛋白组,酪蛋白加钙组,大豆蛋白组和大豆蛋白加钙组大鼠的TC水平分别为(10.56±2.74,7.99±2.19,5.48±0.51和6.81±0.98)mmol/L;ApoB100为(0.46±0.14,0.31±0.12,0.17±0.07和0.21±0.05)g/L.同酪蛋白组相比,其他3组动物的TC和ApoB100浓度显著降低.而各组间TG和HDL-C的变化均无显著性.结论膳食大豆蛋白和/或高钙摄入均可降低高血胆固醇模型大鼠的TC和ApoB100浓度,但对TG和HDL-C的作用不明显.大豆蛋白是这种作用的主要因素,但同时存在大豆蛋白和高钙摄入的相互作用.膳食大豆蛋白和高钙摄入的降血胆固醇机制还需要进一步探讨和研究.     

Effect of egg white and its hydrolysate on stearoyl-CoA desaturase index and fat accumulation in rat tissues

We investigated the dietary effects of egg white (EW) and its hydrolysate (EWH) on fat metabolism in rats. Wistar rats were divided into casein, EW and EWH dietary groups, and fed their respective diet for 8 weeks. Dietary EW and EWH decreased food intake, body weight gain and fat accumulation in the carcass, liver, muscles and adipose tissues, but muscle weight was increased. In addition, dietary EW and EWH decreased stearoyl-CoA desaturase (SCD) indices and glucose-6-phosphate dehydrogenase activity of the liver and gastrocnemius muscle. Dietary EW also increased the fecal excretion of triacylglycerol, cholesterol and total bile acids, and decreased the serum levels of triacylglycerol and leptin. The suppressive effects of dietary EW on food intake and body fat accumulation were weakened by dietary EWH. These findings indicate that EW and EWH, especially EW, are effective in reducing body fat accumulation by regulating hepatic and muscular SCD indices.     

Stimulation of bile-pancreatic zinc, protein and carboxypeptidase secretion in response to various proteins in the rat

The objective of this study was to determine the rate of bile-pancreatic secretion of zinc, protein and carboxypeptidase (CP) in response to three different dietary proteins, egg white (EW), soy protein isolate (SPI) and casein. The infusion of protein into the duodenum stimulated a significant increase in the secretion rate of zinc, protein and CP in bile-pancreatic juice. There was a high degree of correlation between the concentration of zinc and enzyme activity (CPA and CPB) in bile-pancreatic juice indicating that zinc in bile-pancreatic juice is associated with CP activity. The average secretion rate of zinc, protein and CP during the 1-h period after infusion of protein was significantly greater after SPI infusion than after casein. The bile-pancreatic secretion rate of protein, zinc and CPB in response to EW infusion was consistently intermediate between SPI and casein and did not differ statistically from either. Only CPA secretion rate was significantly greater after EW than after casein. Differences in protein digestibility appear to account for the greater pancreatic response to SPI, and this factor may be important in understanding the effect of protein source on zinc bioavailability.     

Preventive effect of soybean resistant proteins against experimental tumorigenesis in rat colon

The insoluble 'high-molecular-weight' fraction (HMF) centrifugally separable after digestion of soy protein isolate with a microbial protease of the exo-type, of which about a quarter is regarded as an indigestible 'resistant protein,' was examined for its preventive effect against colonic tumorigenesis in a model system with male F-344 rats. The rats were intraperitoneally injected with azoxymethane (15 mg/kg BW) once a week for 3 wk and were fed a 20.6% HMF diet (+0.4% DL-Met) or 14.7% casein diet (+0.3% DL-Met) supplemented with 0.2% sodium deoxycholate (DCA) or without supplementation. Twelve wk later, 5 rats of each group were inspected for formation of tumors but no tumors were visible to the naked eye. The DCA-fed casein group was conspicuous for a low count of aberrant crypt foci. At 39 wk, 6 rats of the DCA-fed casein group (n = 10) and 3 rats of the DCA-fed HMF group (n = 9) had a total of 18 tumors with a major axis of 4.0 +/- 0.4 mm and 3 tumors with an axis of 2.0 +/- 0.1 mm, respectively, in contrast to only a single tumor for the DCA-unfed casein group (nil for the DCA-unfed HMF group). The difference in tumor number and size was considered significant between these DCA-fed casein and HMF groups; that is to say, HMF feeding retarded tumor development despite the frequent occurrence of pre-neoplastic lesions. In addition, fecal bile acid excretion was much more elevated by HMF feeding than by casein feeding. It can be assumed from these observations that the antitumorigenicity of HMF is due to the inhibitory effect of soybean resistant proteins on reabsorption as well as the mucosal contact of bile acids in the intestine.     

Zinc supplementation of optimal and suboptimal protein diets 2. Responses of young rats fed protein combinations

The effect of zinc supplementation on the utilization of combination protein sources by and the bioavailability of trace minerals to young rats was studied. Protein combinations included corn meal/soybean meal (CM/SM) and whole wheat/dried egg white solids (WW/EW) formulated to provide protein levels of 7.5% and 15%. Each diet was fed with and without zinc supplements (0, 50, or 100 ppm). Animals were maintained on the experimental diets for 4 weeks, and criteria used for the evaluation included weight gain, hemoglobin concentration, and liver deposition of copper, iron, and zinc. Zinc supplements did not stimulate growth in young rats fed suboptimal levels of either protein combination, and zinc did not appear to be a limiting nutrient in the utilization of a marginal protein level in this study. In this study zinc supplementation had varying effects on the apparent bioavailability of copper or iron, but no general trends were observed. There is the possibility that the effect of zinc on trace mineral availability was influenced by the presences of other dietary factors, such as type and amount of fiber or the presence of phytates, inherent with the types of protein combinations used in the study. As the level of zinc in the diet increased, the amount of zinc accumulating in the liver tended to increase.     

Soybean diet alters the insulin-signaling pathway in the liver of rats recovering from early-life malnutrition

ObjectiveWe investigated if alterations in the insulin-signaling pathway could contribute to reduced hepatic glycogen levels in adult rats subjected to a protein deficiency during intrauterine life and lactation and reared through to recovery on a soybean diet.MethodsRats from mothers fed with 17% or 6% protein (casein) during pregnancy and lactation were maintained with a 17% casein diet (offspring born to and suckled by mothers fed a control diet and subsequently fed the same diet after weaning [CC group] and offspring born to and suckled by mothers fed a control diet and subsequently fed a soybean flour diet with 17% protein after weaning [CS group]), a soybean diet (offspring of mothers fed a low-protein diet and a control diet after weaning [LC group] and offspring of mothers fed a low-protein diet and fed a soybean flour diet containing 17% protein after weaning [LS group]), or a 6% casein diet (offspring of mothers fed a low-protein diet and subsequently fed the same diet after weaning [LL group]) from weaning until 90 d of life.ResultsA soybean diet did not modify basal serum glucose and glucagon concentrations, but raised basal serum insulin and consequently increased the serum insulin/glucose ratio. Insulin receptor and insulin receptor substrate-1 levels were lower in rats fed a soybean diet compared with those maintained with a casein diet. In the LS group, the p85 levels were higher than in the LC group, whereas in CS rats its expression was lower than in CC rats. The expression of p110 was lower in the CS group compared with the CC group and similar in the LS and LC groups. Insulin receptor substrate-1 phosphorylation was similar in the LS, LC, and CS groups and lower compared with the CC group. The insulin receptor substrate-1–p85/phosphatidylinositol 3-kinase association was lower in LS than in LC rats and in CS than in CC rats. Akt phosphorylation was lower in the CS and LS groups than in the CC and LC groups.ConclusionAdult rats maintained with a soybean diet exhibited insulin resistance due, at least in part, to alterations in the early steps of the insulin signal transduction pathway.     

Food intake, energy balance and serum leptin concentrations in rats fed low-protein diets

Studies examining the effects of low-protein diets on food intake and body weight have shown varied results. Many researchers have found low dietary protein to increase food intake, while others have found no effect or even a decrease. In 63 male Sprague-Dawley rats, we examined several low levels of dietary protein (2%, 5%, 8%, 10%, 15% vs. 20% casein) to determine the dose-response relationships between low dietary protein and food intake, body composition, energy balance and serum leptin concentrations. Food intake, over the range of low dietary protein, showed a quasi bell-shaped response curve with peak intake occurring in rats fed 8-10% casein. Peak feeding occurred at or just below the estimated protein requirement of the rats (10-12.5% casein). Compared to the 20% casein controls, food intake was severely reduced in rats fed 2% casein, while it was greater in the other low-protein groups. The amount of body fat steadily increased between the 15% casein group and the 8% casein group, and sharply declined between the 5% casein group and 2% casein group. The change in body fat reflected both the change in food intake and altered energy partitioning. Serum leptin concentrations were greater in rats fed the 5 and 8% casein diets than in control rats fed 20% casein. Serum leptin concentrations were positively associated with body fat content (r(2) = 0.763, P < 0.001). Increased serum leptin concentrations in the presence of increased food intake is suggestive of a state of leptin resistance. This animal model may provide important insights into diet-induced obesity.     

大豆异黄酮类对去卵巢大鼠骨丢失的影响

目的　研究大豆中植物雌激素——异黄酮类对去卵巢大鼠骨丢失的预防作用。方法　将 3月龄 SD雌性大鼠按体重分为 5组 ,每组 1 1只 :假手术对照组 (假手术 +饲含酪蛋白饲料 ,Sham) ;去异黄酮组 (去卵巢 +饲含去异黄酮类大豆分离蛋白饲料 ,Soy- ) ;异黄酮组 (去卵巢 +饲含异黄酮类大豆分离蛋白饲料 ,Soy+) ;酪蛋白组 (去卵巢 +饲含酪蛋白饲料 ,即去卵巢对照组 ,Ovx) ;雌激素对照组 (去卵巢 +饲含酪蛋白饲料 +注射雌二醇 ,E2 )。在实验期第 3周、第 6期和第 9周各进行为期三天的钙代谢试验。第 1 0周末处死大鼠 ,测定骨钙、骨密度 ,并对股骨远端松质骨进行骨组织形态学测量。结果　异黄酮组和雌激素对照组粪钙、尿钙排出量显著低于酪蛋白组和去异黄酮组 (P<0 .0 5) ,钙表观吸收率和钙贮留量显著高于酪蛋白组和去黄酮组 (P<0 .0 5) ,钙代谢呈正平衡。异黄酮组和雌激素对照组骨钙、骨密度高于酪蛋白组和去异黄酮组 (P<0 .0 5)。与雌激素对照组比较 ,异黄酮组骨小梁面积百分率和骨小梁数目明显减少 ,骨小梁间隙明显增宽 (P<0 .0 5) ;但与酪蛋白组和去异黄酮组比较 ,异黄酮组骨小梁面积百分率和骨小梁数目明显增多 ,骨小梁间隙明显减少 (P<0 .0 5)。结论　含有异黄酮类的大豆分离蛋白具有预防骨丢失的作用 ,而?     

Effect of dietary vegetable and animal proteins on atherothrombosis in mice

OBJECTIVE: It is believed that vegetable and fish, but not animal, proteins prevent thrombosis. The present study compared the effect of long-term intake of purified vegetable and animal proteins (casein, pork, egg white, chicken, white and red fish, soybean, and potato) and powders from whole vegetable and animal meats (soybean, pork, chicken, and horse mackerel) on thrombotic tendency. METHODS: Western-style high-fat diets with various proteins were given to mice deficient in apolipoprotein-E and low-density lipoprotein receptor for 8 or 12 wk. Thrombotic tendency was assessed by a laser-induced thrombosis test, severity of atherosclerosis was assessed by morphometric analysis of the aortic lesions, and reactivity of platelets was measured by a shear-induced platelet function test. RESULTS: There was no difference in thrombotic tendency between the vegetable and animal protein diets with the exception of pork protein, which showed a prothrombotic effect. The latter was not observed in animals kept on a high-protein diet. Thrombotic tendency was not affected by preparation of dietary powders from whole pork, chicken, or horse mackerel meats and casein (control), all of which contained the same percentages of protein and lipid. In contrast, soybean powder showed an antithrombotic effect, which was mainly due to an inhibition of atherogenesis rather than to platelet inhibition. CONCLUSION: Neither the purified animal nor the vegetable protein diet affected thrombotic tendency. Soybean powder inhibited atherothrombosis mainly by inhibiting the atherosclerotic process.     

Effects of addition of sulfur-containing amino acids and glycine to soybean protein and casein on serum cholesterol levels of rats

The effects of the supplementation of methionine (Met), cystine (Cys), and glycine (Gly) to soybean protein or casein on serum and liver lipid levels were studied in rats. Rats were fed cholesterol-free diets containing 25% soybean protein or casein supplemented with 0.75% Met, 2.5% Gly, or a combination of these two for 4 weeks. The addition of Met to soybean protein caused a significant increase in serum cholesterol and this was slightly ameliorated when Gly was given simultaneously. In rats fed casein diets, serum cholesterol tended to decrease when Gly, or Met and Gly were added. A simultaneous supplementation of Met and Gly to casein resulted in a reduction of hepatic cholesterol. Cystine added at the 0.6% level did not cause demonstrable changes in lipid concentrations except for a drop in serum triglyceride of the casein group. When 2.0% Gly was added to cholesterol-enriched diets containing 20% protein, serum cholesterol decreased significantly only when the protein source was casein and the level attained was comparable to that observed in rats fed soybean protein. Liver cholesterol was also markedly decreased by the addition of Gly to casein. The results suggest a possible role of Gly in the regulation of serum cholesterol levels by dietary protein.     

Soybean protein hydrolysate improves plasma and liver lipid profiles in rats fed high-cholesterol diet

OBJECTIVE: This investigation attempted to clarify the hypolipidemic effects of non-dialyzed soybean protein hydrolysate (NSPH), which is hydrolyzed by pepsin from soybean acid-precipitated protein (APP), in rats fed a cholesterol-rich diet. METHODS: Forty Sprague-Dawley rats were divided into four groups as the control group (19.7% casein), the APP group (14.7% casein + 5% APP), the NSPH group (14.7% casein + 5% NSPH), and the ISO group (19.7% casein + 0.0013% soy isoflavone). RESULTS: After 12-week experimental period, the APP and NSPH groups had a significant lower plasma total cholesterol, triglycerides, and LDL-cholesterol concentrations compared with the control group. Additionally, the atherosclerosis index in APP and NSPH group had also markedly decreased. Liver cholesterol and triglyceride contents of the APP and NSPH group were significantly lower than those of the control group. There were no different in plasma LDL-C, liver cholesterol and triglycerides between the ISO group and control group. Fecal excretion of neutral steroids and nitrogen compounds was significantly higher in the APP and NSPH groups than that in the control group. An in vitro study also showed that NSPH, compared with casein, obviously decreased cholesterol micellar solubility. CONCLUSION: These results suggested that NSPH may decrease lipid accumulation in the liver and have a hypolipidemic effect by enhancing excretion and inhibiting absorption of lipids.     

Effects of dietary casein and soybean protein on triglyceride turnover in rat liver

We previously found that hepatic lipogenic enzyme induction, fatty acid synthesis, and triglyceride level were markedly lower in rats fed soybean protein than in those fed casein (Iritani et al. (1986): J. Nutr., 116: 190). After labeling triglycerides with tritiated water, the effects of dietary protein on the triglyceride degradation have been investigated. After the injection of tritiated water into rats, the radioactivities of fatty acids and triglycerides reached a plateau in 1-2 days and were markedly lower in the soybean protein group than in the casein group. The decreasing rates of triglyceride radioactivities were similar between the casein and soybean protein groups. The enzyme activities in glycerolipid synthesis were similar between the groups. Therefore, the lowering effects of soybean protein on triglyceride levels appear to be ascribed to triglyceride synthesis (due to fatty acid synthesis) rather than to the degradation.