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To know whether isoflavones are responsible for the hypocholesterolemic effect of soy protein, the effect on plasma cholesterol of isoflavone-free soy protein prepared by column chromatography was examined in rats. Five-week-old male Sprague-Dawley rats were fed cholesterol-enriched AIN-93G diets containing either 20% casein (CAS), 20% soy protein isolate (SPI), 20% isoflavone-free SPI (IF-SPI), 19.7% IF-SPI + 0.3% isoflavone-rich fraction (isoflavone concentrate, IC), or 20% CAS + 0.3% IC for 2 weeks. Plasma total cholesterol concentrations of rats fed SPI and IF-SPI were comparable and were significantly lower than that of rats fed CAS. The addition of IC to the CAS and IF-SPI did not influence plasma cholesterol level. Fecal steroid excretion of the three SPI groups was higher than that of the two CAS groups, whereas the addition of IC showed no effect. Thus, a significant fraction of the cholesterol-lowering effect of SPI in rats can be attributed to the protein content, but the isoflavones and other minor constituents may also play a role.

Many studies have reported the cholesterol-lowering, anti-lipogenic, anti-obesity and anti-hypertensive effects of soy protein. Adipose tissue-specific plasma protein, adiponectin, has anti-atherogenic and anti-insulin-resistance properties. Here, we investigated the effects of soy protein diet on body fat composition, plasma glucose, lipid and adiponectin levels and expression of genes involved in glucose and fatty acid metabolism in obese KK-A y mice. Body weights and adipose tissue weights of mesenteric, epididymal, and brown fat were lower in mice on calorie-restricted diet containing soy protein isolate. Plasma cholesterol, triglyceride, free fatty acid, and glucose levels were also decreased by this diet. Body fat content and plasma glucose levels in mice on a soy protein isolate diet were still lower than those treated with an isocaloric casein-protein-diet. Among the genes related to glucose and fatty acid metabolism, adiponectin mRNA levels in adipose tissue and adiponectin plasma concentrations were elevated in mice on a calorie-restricted diet, although there were no significant differences between soy protein and casein protein groups. Our results indicate that that soy protein diet decreased body fat content and plasma glucose levels more effectively than isocaloric casein-protein diet in obese mice.

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-Conglycinin decreased blood triacylglycerol (TAG) levels in male Wistar adult rats. Liver mitochondrial carnitine palmitoyltransferase activity in the -conglycinin-fed group significantly increased as against the casein-fed group. Hepatic fatty acid synthase activity in the -conglycinin group significantly decreased as against that of the casein-fed group. Fecal fatty acid excretion in the -conglycinin group was significantly higher than in the casein group.Key words: soybean -conglycinin; triacylglycerol (TAG); fatty acid synthase; carnitine palmitoyltransferase; fatty acid excretionIn our previous study, -conglycinin, which is one of the major components of soy protein, lowered plasma triacylglycerol (TAG) levels. 1) Moriyama et al.2) reported that -conglycinin induced -oxidation, downregulation of liver fatty acid synthase, and inhibition of TAG absorption in normal and genetically obese mice under energy restriction conditions. But it appears that more studies are necessary to explain how -conglycinin affects lipid metabolism. In this study, in order to mimic middle-aged adult humans, in whom lifestyle-related diseases occur frequently, we made an experimental design feeding a high cholesterol diet ad libitum to normal adult rats to induce dietary hyperlipidemia, and examined the effects of -conglycinin on liver lipid metabolic enzymes and fecal fat excretion to explain how -conglycinin reduces plasma TAG.All animals were treated in accordance with the guidelines established by the Japanese Society of Nutrition and Food Science (Law No. 105 and Notification No. 6 of the Japanese Government). -Conglycinin was prepared according to the method described by Saito.3) Animals, diets, and measurements were performed according to the our previous study.1) In brief, 20-week old male Wistar rats were fed experimental diets containing 20% casein or -conglycinin with free access for 10 d. Each diet contained 0.5% cholesterol and 0.125% sodium cholate, and the further components were based on the AIN-93G formula. On day 11, after 6 h of food deprivation (0730-1330), blood was withdrawn from the abdominal aorta into a heparinized syringe under intraperitoneal sodium pentobarbital anesthesia. Livers were excised, rinsed, and weighed, and then stored at À80 C pending analysis. Plasma was separated by centrifugation and stored at À80C pending analysis.All results of this study are shown in Table 1. Food consumption in the -conglycinin group increased compared with the casein group. On the other hand, there was no difference in weight gain between these groups. The plasma TAG level in the -conglycinin group was significantly lower than that in the casein group. There was no difference in plasma glucose concentration between groups. Liver weight in theconglycinin group was significantly lower than in the casein group. Hepatic carnitine palmitoyltransferase activity in the -conglycinin group was significantly higher than in the casein group. Fatty acid synthase activity in the -conglycinin group was significantly lower than th...

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