Soy cotyledon fiber products reduce plasma lipids.

This study was designed to test the hypocholesterolemic effect of soy cotyledon fiber in the diet as ready-to-eat cereal and white bread, in free-living subjects having mildly elevated, fasting plasma total cholesterol levels. Twenty subjects completed a 15-week double-blind crossover design protocol. It consisted of two 6-week test periods and a 3-week rest period in between the two test periods. Subjects were randomly allotted to two test groups with comparable initial cholesterol levels. Fifteen grams of dietary fiber per day from soy cotyledon fiber was supplemented in three divided doses (equivalent to 20 g Fibrim soy fiber/day). Dietary records were kept for 3 consecutive days for each test period and were calculated using a computer program. Subjects were asked to maintain their normal eating habits and body weights throughout the 15-week protocol. There were no significant differences in nutrient intake between the two supplementation periods based on 3 day dietary records, except that the amount of fiber intake was significantly higher when soy cotyledon fiber was supplemented (24 g vs. 13 g/day). Soy cotyledon fiber supplementation did not produce visible intolerance. Body weights and blood pressures were not significantly affected. Soy cotyledon fiber supplementation significantly lowered plasma total cholesterol by 7.7% (from 240 to 222 mg/dl, P less than 0.01) and LDL-cholesterol by 7.4% (from 159 to 145 mg/dl, P less than 0.04). Plasma HDL-cholesterol and total triglycerides were not significantly affected.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of soy fiber and soy protein on cholesterol metabolism and atherosclerosis in rabbits.

The effect of dietary fiber isolated from dehulled, defatted soybean seeds on cholesterol (CHOL) metabolism and atherosclerosis in rabbits was studied alone and in combination with isolated soy protein (ISP). Soy fiber (SF) contains both cellulosic and non-cellulosic dietary fiber. Based on the official AOAC method, soy fibers contains 75% total dietary fiber. Rabbits at 6 months of age were randomly assigned to 1 of 4 dietary treatments. All rabbits received either a casein or ISP-based diet with cellulose or SF as the only dietary fiber source for 36 weeks. Fasting blood samples and feces were collected and analyzed for lipids from individual rabbits. The entire aorta was removed and fixed, and sudanophilic stained lesions were examined visually. Rabbits consuming the SF and/or ISP diets had lower plasma CHOL levels and lower incidence of atherosclerotic lesions relative to the rabbits fed the casein-based cellulose diets. Rabbits consuming the SF and/or ISP diets also had a lower CHOL content in their liver and heart. Rabbits fed ISP-based diets had consistently increased fecal bile acid excretion, whereas rabbits fed diets containing SF had increased fecal and cholesterol concentration. These results suggest a complementary role for SF and ISP in preventing atherosclerosis in rabbits.

Effects of soy polysaccharide on postprandial plasma glucose, insulin, glucagon, pancreatic polypeptide, somatostatin, and triglyceride in obese diabetic patients.

The effect of soy polysaccharide on postprandial plasma glucose levels was examined in a crossover experiment involving seven obese noninsulin dependent maturity-onset diabetic patients fed a standard meal without or with 10 g of this fiber source. Postprandial concentrations of plasma insulin, glucagon, pancreatic polypeptide, and somatostatin were measured to explore the mechanism of action. The effect on plasma triglyceride levels was also studied. Supplementation of soy polysaccharide significantly enhanced return of serum glucose levels towards fasting level during the latter half of the meal test. Addition of soy polysaccharide had no effect on plasma insulin levels but appeared (p greater than 0.05) to lessen postprandial increases in glucagon and pancreatic polypeptide levels while it raised somatostatin levels. Soy polysaccharide significantly reduced the rise of postprandial plasma triglyceride levels. The changes in plasma glucagon, pancreatic polypeptide, and somatostatin levels may have been instrumental in the observed postprandial glucose and triglyceride effects.

Soy fiber improves lipid and carbohydrate metabolism in primary hyperlipidemic subjects.

This study was designed to evaluate the effects of soy fiber, a natural source of dietary fiber that consists of both cellulosic and noncellulosic dietary fiber, on human plasma lipoprotein lipids and glucose tolerance in patients with primary hyperlipidemia. Supplementing 25 g of soy fiber per day provided a significant additional reduction of plasma total-cholesterol by 13 mg/dl (P less than 0.04) and LDL cholesterol by 12 mg/dl (P less than 0.05) beyond that previously achieved by treatment with an NIH Type II-A low-fat, low-cholesterol diet for 12 weeks in Type II-A hypercholesterolemic patients. There were no effects on HDL cholesterol or apoprotein A-I and A-II levels. The hypocholesterolemic effect was greater than in the hyperlipidemic patients with impaired glucose tolerance. Soy fiber supplementation also significantly reduced insulin responses to oral glucose challenge by 20% in Type II-A hypercholesterolemic and by 16.5% in Type IV hypertriglyceridemic patients. Results from this study suggest that supplementing the diet with soy fiber may be beneficial in dietary management of hyperlipidemia in patients with hypercholesterolemia and particularly in hyperlipidemic patients with hyperinsulinemia and impaired glucose tolerance.

Effects of soybean polysaccharide on plasma lipids.

Free-living volunteers with mild to moderate hypercholesteremia added 25 gm soybean polysaccharide or starch placebo in crouton or cookie form to their normal, daily diets. A total of 31 persons completed the blind, crossover design, 8-week, experimental protocol. Subjects ingesting soybean polysaccharide prior to placebo showed an 11% decrease (from 252 to 224 mg/dl) in total plasma cholesterol; those who followed placebo with fiber showed a 5% decrease (from 241 to 230 mg/dl). Starch placebo was associated with a 2% decrease in total cholesterol when consumed first and a 4% increase when consumed following the fiber consumption period. High-density-lipoprotein (HDL) cholesterol decreased 8% and 6% from initial values during the first period for the fiber and starch groups, respectively. HDL cholesterol increased 2% but decreased 1% during the second period for starch and fiber, respectively. No significant changes in triglyceride levels occurred. The data indicate that soybean polysaccharide fiber promotes a significant decrease in plasma cholesterol in persons with mild to moderate hypercholesteremia. The addition of fiber may represent an important adjunct to traditional fat- and cholesterol-controlled diets for such persons.

Bioavailability of copper in isolated soybean protein using the rat as an experimental model.

The bioavailability of copper from isolated soybean protein was evaluated with growing rats. Copper depletion and repletion feeding techniques were used to evaluate the biologically available copper. Serum and liver copper contents were used as physiological indication to determine the bioavailability of copper in the diet. Sprague-Dawley male weanling rats were fed a diet low in copper for 21-42 days and then transferred to the test diets containing different levels of copper from copper carbonate or isolated soybean proteins for 7-14 days. Statistical analyses of serum and liver copper by using the slope-ratio bioassay were performed to determine the relative potency of the test products to the copper carbonate standard. The results from four feeding experiments indicate that 1) hypocupremia was produced by feeding a low copper basal diet to weanling rats after 28 days, 2) the time required to replete serum and liver copper was 7 days and 3) copper was available equally from isolated soybean protein and copper carbonate.

Effects of soy polysaccharide on gastrointestinal functions, nutrient balance, steroid excretions, glucose tolerance, serum lipids, and other parameters in humans.

A diet-controlled study with a cross-over design was conducted to determine the effect of soy polysaccharide on gastrointestinal functions, nutrient balance, steroid excretion, blood lipid levels, postprandial serum glucose response, and other blood parameters in healthy male human subjects. A total of 14 college students was selected to participate in the study on a voluntary basis and each served as his own control. The study had two 17-day feeding periods. During the first feeding period, half of the subjects served as controls, the other as experimentals. During the second feeding period, treatments were crossed. When serving as controls, subjects consumed a low-fiber basal diet; when serving as experimentals, the same diet was supplemented with 25 g/day of soy polysaccharide. Blood samples taken at the beginning (days -1 and 1) and at the end (days 17 and 18) of each period revealed no changes in serum lipid levels or other blood parameters by soy polysaccharide supplementation. Nutrient balance and fecal transit studies revealed a significant increase in fecal wet weight and fecal water content, but no changes in total dry weight, fecal neutral steroid, bile salt, protein, and mineral contents. Glucose tolerance tests conducted during each period revealed that addition of soy polysaccharide to the glucose solution significantly reduced the reactive hypoglycemia at 180 min. Results of the present study suggest that in healthy male subjects, supplementation of soy polysaccharide can result in an increase in wet fecal content and possibly some improvement in glucose tolerance response.

Effect of phytate:zinc molar ratio and isolated soybean protein on zinc bioavailability.

The effect of phytate to zinc (Zn) molar ratio on zinc bioavailability was evaluated in rats. The bioavailability was determined by giving an oral dose of 65Zn and measuring the liver uptake and disappearance from the gastrointestinal tract after 4 hours and fecal and urinary 65Zn excretion from 24 to 168 hours. Rats were fed a diet containing 12 ppm zinc from zinc sulfate with and without phytic acid from sodium phytate for 14 days. At the end of 14 days feeding, the rats were intubated with a homogenized diet containing 12 ppm zinc, one microCi 65Zn and graded levels of phytic acid so that the phytate:Zn molar ratio varied from 0 to 100. Zinc bioavailability was significantly reduced only in the rats fed diets containing phytate and intubated diet containing phytate:zinc molar ratio of 12.5 and above. The results from this study also indicated that measuring 65Zn disappearance and uptake was a valid bioassay for determining zinc bioavailability. The effect of isolated soybean protein on extrinsic zinc bioavailability was also evaluated in rats fed zinc adequate and zinc deficient diets. The results showed that zinc bioavailability was significantly reduced by replacing egg white protein with isolated soybean protein only when the rats were fed zinc deficient diet prior to single oral dose of 65Zn mixed with test proteins. The effect of isolated soybean protein on intrinsic zinc bioavailability for the growing rats was also evaluated. The results demonstrated that the zinc bioavailability in isolated soybean protein can be improved by fortifying with zinc so that the phytate:Zn molar ratio is less than 10.

Comparative measurement of zinc absorption in rats with stable isotope 70Zn and radioisotope 65Zn.

The use of stable isotopes in a study on zinc bioavailability was evaluated in rats by comparing the zinc absorption of a stable isotope 70Zn and a radioisotope 65Zn simultaneously. The rats of low zinc status were obtained by feeding 1.2% phytic acid from sodium phytate and 12 ppm zinc from zinc sulfate in a semipurified diet for 14 days. The rats were then randomly assigned into five groups of ten rats. The rats were intubated with a test diet mixture with a phytate:zinc molar ratio of 0, 6.25, 12.5, 25 or 50 along with one microCi of 65Zn and 0.02 mg of 70Zn in 2.5 ml of intubating solution. Four hours after the intubation, rats were allowed to consume the diets having the same phytate:zinc ratio as used for intubation ad libitum. Feces were collected every 24 hours for a total of 168 hours. The 65Zn and 70Zn content of diets and fecal samples were determined and the percent of zinc absorption was calculated. The results of this study indicated that the zinc absorption determined by these two isotopes were highly correlated with a correlation coefficient ratio of 0.914.

Determinants of hypocholesterolemic response to soy and animal protein-based diets.

The effect of substituting soy for animal protein in mixed diets was determined in young men with mildly elevated plasma cholesterol, 218 to 307 mg/dl. The diets were low in cholesterol, 200 mg/day, with 13 to 16% of energy as protein, 30 to 35% as fat, and a polyunsaturated to saturated fat ratio of 0.5. Of protein 65% was from either mixed animal proteins or isolated soy protein products made comparable by the addition of extracted animal fats. Fresh egg yolk was added to balance the cholesterol content of the diets. Proteins from grains and vegetables were identical in both menus and contributed about 35% of dietary protein. Twenty of 24 subjects decreased plasma cholesterol at the end of the protocol. Subjects were classified as responders or nonresponders as a function of greater or lesser than mean reduction in cholesterol for the groups. Mean decreases in plasma cholesterol, 16 and 13%, for responders in the animal and soy groups were significant, p less than 0.01 and 0.05, respectively. Responders in both groups had higher initial plasma cholesterol values than nonresponders. Although plasma high-density lipoprotein cholesterol decreased slightly, the high-density lipoprotein cholesterol to cholesterol ratio (high-density lipoprotein cholesterol/total cholesterol) remained constant for most individuals. The hypocholesterolemic effects were similar for both animal and soy protein (p less than 0.05) and fat (p less than 0.05) while on the experimental diet. All groups significantly decreased dietary cholesterol (p less than 0.001).

Effect of isolated soybean protein on magnesium bioavailability.

The effects of isolated soybean protein and animal protein on magnesium bioavailability were evaluated in this study. Total serum magnesium and femur bone ash magnesium values were used to evaluate the relative bioavailability of magnesium in diets in which ANRC casein, isolated soybean proteins, autoclaved isolated soybean proteins or lyophilized beef served as protein sources. Low magnesium basal diets were supplemented with graded levels of magnesium from magnesium carbonate and fed to weanling Sprague-Dawley rats for 28 days. Serum and femur bone ash magnesium were analyzed by atomic absorption spectrophotometry. Statistical analysis of serum and bone ash magnesium using a slope-ratio bioassay indicated that the protein sources did not have a significant effect on the bioavailability of magnesium.