Influence of diets containing cow's milk or soy protein beverage on plasma lipids in children with familial hypercholesterolemia.

The present article summarizes the effects of diets containing either cow's milk or soy protein beverage on plasma lipids and lipoproteins in children with familial hypercholesterolemia. After a stabilization period of 6 weeks without any hypolipemic medication, 10 subjects aged 6-12 years were randomly assigned to either cow's milk or soy protein beverage with subsequent crossover after a washout period, each of 4 weeks duration. During the experimental periods, subjects were fed diets containing 20% of energy as protein, of which 35% was from cow's milk protein or soy protein isolate, 28% of energy as fat with a polyunsaturated:monounsaturated:saturated fat ratio of 1:3:3, and less than 200 mg/day of cholesterol. The soy protein beverage, compared to cow's milk, induced significant reductions in plasma triglycerides and very-low-density lipoprotein cholesterol, as well as a significant increase in high-density lipoprotein cholesterol, indicating that consumption of soy protein beverage may be beneficial for the prevention of coronary heart disease in children with familial hypercholesterolemia.

Effects of a soy-protein beverage on plasma lipoproteins in children with familial hypercholesterolemia.

The effects of soy protein (35% of protein energy) given as a beverage and those of cow-milk proteins were investigated on plasma lipoprotein concentrations in children with familial hypercholesterolemia (FH). Subjects were randomly assigned to either the soy-protein or cow-milk-protein experimental period, with subsequent crossover after a washout period, each period lasting 4 wk. Diets were planned to provide 20% energy as protein, 28% as fat (polyunsaturated:monounsaturated:saturated fatty acids, 1:3:3) and less than 200 mg cholesterol/d. No changes were observed in either plasma cholesterol, low-density-lipoprotein cholesterol, or apolipoprotein concentrations. However, the soy beverage significantly reduced the concentrations of triglyceride and very-low-density-lipoprotein cholesterol (P less than 0.05) and significantly increased the concentrations of high-density-lipoprotein cholesterol (HDL-C) and HDL3-C (P less than 0.04 and P less than 0.03, respectively). These results indicate that the administration of soy protein may induce clinically beneficial effects in children with FH.

In vivo rat assay for true protein digestibility: collaborative study.

Eight laboratories participated in a collaborative study to estimate precision of a standardized rat assay for determining true protein digestibility in selected animal, fish, and cereal products. Each of 7 test protein sources (casein, tuna fish, macaroni/cheese, pea protein concentrate, rolled oats, pinto beans, and nonfat dried milk) was fed as the sole source of protein at a 10% protein level in mixed diets. Each diet was fed to 2 replicate groups of 4 rats each for a 4-day acclimation period and a 5-day balance period. Mean digestibilities ranged from 98.6% for casein to 72.6% for pinto beans. Repeatability standard deviations ranged from 0.5 to 2.0%; the mean relative standard deviation for repeatability was 0.9% (range 0.5-2.8%). Reproducibility standard deviations ranged from 1.2 to 3.2%, and the mean relative standard deviation for reproducibility was 2.4% (range 1.3-4.4%). The method has been approved interim official first action for determining true protein digestibility in foods and ingredients.

In vitro assay for protein digestibility: interlaboratory study.

True protein digestibilities of 17 protein sources were estimated by 6 laboratories using an in vitro, 3-enzyme digestion system in a pH stat. Samples from animal, vegetable, and mixed food sources were freeze-dried (if not already dried), ground, mixed, and shipped to each collaborator along with a sodium caseinate standard and trypsin, chymotrypsin, and peptidase. The uptake of titrant during enzymatic digestion was used to calculate estimates of digestibility. Digestibilities ranged from 100% for casein to 89.9% for whole wheat cereal. Mean relative standard deviations for repeatability were 1.4% for rolled oats and less than 1% for the remaining 16 samples. Mean relative standard deviations for reproducibility ranged from 5.0 to 0.8%; values were less than 2.5% for 13 of the 17 samples.

The estimation of 'available lysine' in human foods by three chemical procedures.

Seventeen test foods were each analyzed by four methods. Total lysine was measured by conventional amino acid analysis. Reactive lysine was measured with either fluorodinitrobenzene, o-phthalaldehyde or a differential dye-binding procedure. The results were then compared with another group's results from rat growth assays of the same samples for availably lysine. A sample of deliberately heat-damaged milk powder gave a rat assay value corresponding to 64% of its total lysine content; other values were all higher and on average 99% for 7 animal products, and 87% for 9 vegetable products. The correlation coefficient between the two sets of values was 0.95. The 'reactive lysine' procedures failed to give a better prediction of the rat values.

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.

Absorption of selenium from milk protein and isolated soy protein formulas in preschool children: studies using stable isotope tracer 74Se.

Absorption of selenium as the stable isotopic tracer [74Se]selenite was measured in four preschool children who were receiving liquid formula diets based on casein, isolated soy protein, and a 50:50 combination of the two protein sources. The children were in continuous ambulatory balance studies within the Clinical Research Center during three consecutive 11-day collection periods. The enrichment of the 74Se/76Se ratio in feces was measured by radiochemical neutron activation analysis, with fractional absorption estimated therefrom. Mean fractional absorption of selenium (+/- SD) from the formulas based on milk, isolated soy protein, and milk-soy were 64.2 +/- 14.6, 73.4 +/- 19.0, and 45.0 +/- 10.9%, respectively, with the combined formula having a significantly lower intestinal uptake for added selenite than the casein formula. Stable isotopes of selenium are safe and potentially useful tools for examining its bioavailability in the diets of young children.

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.

A long-term metabolic balance study in young men to assess the nutritional quality of an isolated soy protein and beef proteins.

To evaluate the capacity of an isolated soy protein to maintain long-term protein nutritional status in healthy young adult men, an 84-day metabolic balance experiment was conducted in eight subjects. The sole source of protein intake was provided by the isolated soy protein, given at a level of 0.8 g (N X 6.25) per kg per day. In a second and similar study, four young men received 0.8 g protein and three subjects 0.68 g protein per kg per day from beef proteins for 60 to 81 days. Body weight, nitrogen balance, blood chemistries, and body composition (whole body 40K) were monitored throughout each study. Body nitrogen balances were maintained within the range of N equilibrium in both diet groups. Body cell mass, as judged from 40K measurements, did not reveal any deterioration in protein nutritional status. These observations confirm the prediction, derived from previous short-term. N balance studies, that the nutritional quality of isolated soy protein is high and that this plant protein can serve as the sole source of essential amino acids and nitrogen for protein maintenance in adults.

Nitrogen balance studies in young men to assess the protein quality of an isolated soy protein in relation to meat proteins.

The protein nutritional value of an isolated soy protein was examined in healthy young men during 10-day N-balance periods. In the first study (expt 1), 10 young men received a diet providing a test protein (N X 6.25) intake of 0.6 g protein per kilogram per day with nitrogen from either lean beef, isolated soy protein or various combinations of the two sources. No differences in N balance, digestibility or net protein utilization were observed when the soy protein replaced beef. In the second study (expt 2), three separate groups of seven young men each received graded intakes of either beef or an isonitrogenous mixture of beef and the isolated soy protein or dried skim milk. An estimate was made of the N intake from each source required for N equilibrium. These values were 116, 106 and 103 mg N/kg per day, respectively. No statistically significant differences were found among the three dietary groups. Thus, the protein quality of the isolated soy protein appears to be comparable to that of animal protein sources such as milk and beef.

Nitrogen balance response in young men given one of two isolated soy proteins or milk proteins.

The protein nutritional value of two isolated soy proteins was compared with that of dried skim milk proteins in healthy young men. Eight subjects received one of the isolated soy proteins and six subjects received the dried skim milk as the test protein source. Each protein was tested at intakes of 0.35, 0.45, 0.55 and 0.65 g protein (N X 6.25) per kilogram per day during 10-day diet periods separated by break periods of 3 days and a 1-day protein-free period. Nitrogen balances were determined for the final 5 days of each experimental diet period. From regression analysis of nitrogen intake minus nitrogen output data, intakes of each protein source to meet mean nitrogen requirements were 124, 146 and 144 mg N/kg per day for the two isolated soy proteins and skim milk protein, respectively. It is concluded that well-processed isolated soy proteins are indistinguishable from milk as a protein source for maintenance of short-term N balance in adult human nutrition.

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.

Simultaneous determination of absorption of selenium from poultry meat and selenite in young men: application of a triple stable-isotope method.

A triple stable-isotope method was used to estimate simultaneously selenium absorption from poultry meat intrinsically labelled with 74Se and from an extrinsic tracer of 76SeO3(2-) in four young adult men. The subjects received an experimental diet based on chicken meat as the source of protein. Two diet periods, lasting from 5 to 10 d, depending on the frequency of stool output for each subject, were conducted to allow duplicate determinations within each subject of Se absorption from both sources. Absorption of Se was determined by the faecal isotope balance procedure through monitoring the stable isotopes 74Se, 76Se and 80Se by means of radiochemical neutron activation analysis. For the separate periods, mean (with SEM) absorption of 74Se from the intrinsically-labelled poultry meat was 70.9 (1.5)% and 72.0 (2.5)%. The absorption of Se from 76SeO3(2-) was 34.7 (5.5)% and 37.6 (3.2)% during the same periods. From these results it is concluded that, under the present experimental conditions, the intrinsic and extrinsic Se isotopes did not form a common pool before absorption. Possible reasons for this are discussed.

Bioavailability of zinc from a diet based on isolated soy protein: application in young men of the stable isotope tracer, 70Zn.

With the aid of the stable isotope, 70Zn, as a tracer and neutron activation analysis, a combination of extrinsic labeling of meals and fecal monitoring of isotope excretion was used as a safe and noninvasive approach for assessing the effects of the vegetable (soy) and animal (milk, beef) proteins on the absorption of zinc in healthy, adult human volunteers. A known amount of 70Zn was added as ZnCl2, to six consecutive meals over a 2-day period during which either one of three isonitrogenous liquid formulas (skim milk; soy isolate; or a 50:50 mixture) or one of two bologna sausages (soy isolate of beef) were given. The mean absorption of 70Zn from milk, soy and soy/milk was 41 +/- 4, 34 +/- 4, and 41 +/- 7% (mean +/- SEM), respectively, the presence of soy protein having no effect on absorption of the extrinsic label. For beef bologna and soy bologna, fractional absorption of the 70Zn tracer was 41 +/- 4 and 30 +/- 3%, respectively. Beef might favor absorption of extrinsic zinc. The kinetics of isotope excretion, pooling procedures, for stool samples and the utility of fecal markers were also evaluated.

Absorption of dietary zinc in man: comparison of intrinsic and extrinsic labels using a triple stable isotope method.

Determination of true absorption of dietary minerals in human subjects using "extrinsic-tag" approach with stable isotopes requires establishment of its validity. The present study was conducted to test with quantitative aspects absorption of an extrinsic-tag of zinc labeled with 70Zn as compared with an "intrinsic-tag" of the mineral as 68Zn-labeled chicken meat given simultaneously to health male subjects. Three diet periods were used in which diet modulation with respect to zinc dialy intake and nature of protein source (chicken/soy protein isolate) was also examined. Absorption was measured via quantitative fecal isotope balance of 64Zn, 68Zn, 70Zn. For the three diet period 1 (protein: chicken; Zn intake: ZN intake: 10 to 11 mg/day), 2 (protein: chicken/soy protein isolate, 50/50; Zn intake: 10 to 11 mg/day), and 3 (protein: chicken; Zn intake: 7 mg/day), fractional absorption of the extrinsic tag (mean +/- 1 SEM) was 0.46 +/- 0.06, 0.46 +/- 0.06, and 0.66 +/- 0.04 respectively. The comparable values for intrinsic 68Zn were 0.57 +/- 0.06, 0.57 +/- 0.06, and 0.72 +/- 0.04. There was a highly significant correlation (r=0.91), between zinc absorption from the two labels. However, absorption of intrinsic 68Zn was significantly higher (p less than 0.02) during all periods than that for the extrinsic 70Zn. A 50% replacement of protein from chicken meat with the soy protein isolate did not later fractional absorption of zinc from either tag. The ratio of fractional absorption of the extrinsic/intrinsic tag (mean +/- 1 SEM) was 0.79 +/- 0.06, 0.79 +/- 0.04, and 0.92 +/- 0.03 for periods 1, 2, 3, respectively.

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.

Intrinsic labelling of chicken meat with stable isotopes of zinc, for intended use in human feeding studies: feasibility and design considerations.

1. The feasibility of intrinsically labelling poultry meat with the stable isotopes 68Zn and 70Zn was investigated. 2. Chickens (1-d-old) were gavaged with solutions of 68Zn and 70Zn several times over a 42 d period. 3. Isotopic analysis of edible tissues has shown that they were significantly enriched with respect to the gavaged isotope and that the extent of isotopic enrichment achieved was sufficient to permit their use in human feeding experiments designed to investigate availability of native Zn from such food models. 4. The absolute efficiency of retention of the stable isotopes from gavage solutions in the edible tissues has been calculated to be 2-3% of the administered dose; methods have been suggested to enhance this value, based on considerations of utilization of dietary Zn.