Intact Soy Protein Research Articles

Neuromodulatory Properties of Soyabean Bioactive Proteins and Peptides

Soy consumption has been associated with many potential health benefits in reducing chronic diseases such as obesity, cardiovascular disease, insulin-resistance/type II diabetes, certain type of cancers, and immune disorders. These physiological functions have been attributed to soy proteins either as intact soy protein or more commonly as functional or bioactive peptides derived from soybean processing. These findings have led to the approval of a health claim in the USA regarding the ability of soy proteins in reducing the risk for coronary heart disease and the acceptance of a health claim in Canada that soy protein can help lower cholesterol levels. Using different approaches, many soy bioactive peptides that have a variety of physiological functions such as hypolipidemic, anti-hypertensive, and anti-cancer properties, and anti-inflammatory, antioxidant, and immunomodulatory effects have been identified. Some soy peptides like lunasin and soymorphins possess more than one of these properties and play a role in the prevention of multiple chronic diseases. Overall, progress has been made in understanding the functional and bioactive components of soy. However, more studies are required to further identify their target organs, and elucidate their biological mechanisms of action in order to be potentially used as functional foods or even therapeutics for the prevention or treatment of chronic diseases.

Soybean Bioactive Peptides and Their Functional Properties.

Soy consumption has been associated with many potential health benefits in reducing chronic diseases such as obesity, cardiovascular disease, insulin-resistance/type II diabetes, certain type of cancers, and immune disorders. These physiological functions have been attributed to soy proteins either as intact soy protein or more commonly as functional or bioactive peptides derived from soybean processing. These findings have led to the approval of a health claim in the USA regarding the ability of soy proteins in reducing the risk for coronary heart disease and the acceptance of a health claim in Canada that soy protein can help lower cholesterol levels. Using different approaches, many soy bioactive peptides that have a variety of physiological functions such as hypolipidemic, anti-hypertensive, and anti-cancer properties, and anti-inflammatory, antioxidant, and immunomodulatory effects have been identified. Some soy peptides like lunasin and soymorphins possess more than one of these properties and play a role in the prevention of multiple chronic diseases. Overall, progress has been made in understanding the functional and bioactive components of soy. However, more studies are required to further identify their target organs, and elucidate their biological mechanisms of action in order to be potentially used as functional foods or even therapeutics for the prevention or treatment of chronic diseases.

Accurate and Sensitive Quantification of Soy Proteins in Raw and Processed Food by Sandwich ELISA

Soy belongs to the so called 'Big 8' allergens and following food labeling directives of many different countries soy has to be labeled as ingredient if used in food. Allergen labeling statements enable sensitized patients to avoid the intake of food containing soy. The major allergenic proteins in soy are Glycinin (Gly m 6) and s-Conglycinin (Gly m 5). The sandwich ELISA RIDASCREEN®FAST Soya quantifies these two proteins in unprocessed as well as in processed food. The following performance characteristics were validated: Selectivity, limit of detection, limit of quantification, precision, recovery, and robustness. First results from proficiency test rounds verified these validation results. In summary, the assay shows high precision and very good recoveries for all different types of samples. It is robust against normal occurring variation within a laboratory. Compared to other test-kits on the market, this ELISA is suitable for the recognition of unheated to strongly heated soy proteins in various foods. Therefore the test can be used for most samples on the market that contain intact soy protein.

Partially hydrolyzed soy protein shows enhanced transport of amino acids compared to nonhydrolyzed protein across an intestinal epithelial cell monolayer.

Consumption of protein hydrolysates has been proposed to stimulate muscle anabolism more than intact (nonhydrolyzed) proteins via accelerated delivery of amino acids for muscle protein synthesis (MPS). We evaluated whether the rate of amino acid uptake and transport across intestinal cells was enhanced for soy protein hydrolysates versus nonhydrolyzed soy protein. Intact and partially hydrolyzed proteins were subject to simulated gut digestion and applied to the apical surface of Caco-2 monolayers. Basolateral media was harvested after 3 h and quantitatively analyzed for free amino acids using ion-exchange chromatography and comparison to an included reference standard. Basolateral concentrations of all amino acids were higher (mean 32%) for hydrolyzed versus nonhydrolyzed protein with the greatest differences in histidine, lysine, and valine. Scale-up production of the soy protein hydrolysate did not diminish its enhanced absorption properties. These data support the hypothesis that hydrolyzed soy protein may provide dietary amino acids that are more rapidly transported across the intestinal epithelium versus intact soy protein. This would be important under conditions where rapid and increased levels of amino acids are needed such as in the stimulation of MPS.

Changes in Structural Characteristics of Antioxidative Soy Protein Hydrolysates Resulting from Scavenging of Hydroxyl Radicals

Antioxidant activity of soy protein (SP) and its hydrolyzed peptides has been widely reported. During scavenging of radicals, these antioxidative compounds would be oxidatively modified, but their fate is not understood. The objective of this study was to evaluate the structural characteristics of SP hydrolysates (SPHs), compared to intact SP, when used to neutralize hydroxyl radicals (•OH). SPHs with degree of hydrolysis (DH) 1 to 5 were prepared with Alcalase. Antioxidant activity of SPHs was confirmed by lipid oxidation inhibition measured with thiobarbituric acid-reactive substances, ability to scavenge 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radicals, and ferrous ion chelation capability. Oxidation of SPHs was initiated by reaction with •OH generated from 0.1 mM FeCl(3) , 20 mM H(2) O(2) , and 1.0 mM ascorbate. After oxidative stress, carbonyl content of SPHs increased by 2- to 3-fold and sulfhydryl groups decreased by up to 42% compared to nonoxidized samples (P < 0.05). Methionine, histidine, and lysine residues were significantly reduced as a result of inactivating •OH (P < 0.05). Attenuated total reflectance-Fourier transform infrared and circular dichroism spectroscopy suggested the conversion of helical structure to strands and turns. Oxidatively modified SPHs had a lower intrinsic fluorescence intensity but similar solubility when compared to nonoxidized samples. These structural changes due to •OH stress may impact the ingredient interaction and functionality of SPHs in food products.

Endogenous and Exogenous Equol Are Antiestrogenic in Reproductive Tissues of Apolipoprotein E-Null Mice1–3

Equol is an isoflavone (IF) metabolite produced by intestinal microbiota in a subset of people consuming dietary soy. Equol producers may show different responses to soy foods and phenotypes related to cancer risk. Here, we assessed the effects of soy IF, endogenous microbial equol production, and dietary racemic equol in a 3 × 2 × 2 factorial experiment using gnotobiotic apoE-null mice ( n = 9–11/group/sex). At age 3–6 wk, equol-producing microbiota were introduced to one-half of the colony ( n = 122). At age 6 wk, mice were randomized to receive a diet that contained 1 of 3 protein sources: casein and lactalbumin, alcohol-washed soy protein (low IF), and intact soy protein (high IF), with total IF amounts of 0, 42, and 566 mg/kg diet, respectively. One-half of each diet group also received racemic equol (291 mg/kg diet). After 16 wk of dietary treatment, serum isoflavonoid profiles varied with sex, soy IF amount, and intestinal microbiota status. There were no treatment effects on tissues of male mice. In females, reproductive tissue phenotypes differed by equol-producing ability (i.e., microbiota status) but not dietary equol or IF content. Equol producers had lower uterine weight, vaginal epithelial thickness, total uterine area, endometrial area, and endometrial luminal epithelial height compared with nonproducers ( P < 0.05 for all), with an association between microbiota status and estrous cycle ( P> chi-square = 0.03). Exogenous equol reduced expression of progesterone receptor (PGR) and the proliferation marker Ki67 ( P< 0.0001) in vaginal epithelium and endometrium; for endogenous equol, only PGR was reduced ( P <0.0005). Our findings indicate that equol diminishes estrogen-dependent tissue responses in apoE-null mice.

Beneficial effects of soy peptide fractions on lipid profiles and appetite‐related hormones in obese rats induced by high fat diet

This study aimed at investigating whether dietary peptides had beneficial effects on lowering obesity and body fat as compared with intact protein. Sprague Dawley male rats were divided into four groups (n=8/group) and fed experimental diets containing 18% fat diet with different nitrogen sources and levels, respectively; 10 % soy protein isolate (10SPI), 25% soy protein isolate (25SPI), 25% soy protein hydrolysates (25SPH) and 25% soy macropeptide fractions (25SPP, MW≥10000) for six weeks. Weight gain was significantly higher in 25% nitrogen sources‐fed groups than in 10% group (10SPI). In 25SPP, perirenal fat mass and serum total lipid significantly lower than in other groups. As for appetite‐related hormones, ghrelin was not shown to be different among groups but leptin significantly decreased in 25SPP. It can be concluded that soy peptide fractions as compared with intact soy protein may have beneficial effects on reducing fat mass and serum lipid as well as appetite regulation.

Effects of Soy Protein, its Hydrolysate and Peptide Fraction on Lipid Metabolism and Appetite-Related Hormones in Rats

This study was aimed to investigate whether soy protein hydrolysates had beneficial effects on serum and tissue lipid contents and appetite-related hormones as compared with intact soy protein. Four-week-old male Sprague-Dawley rats were fed AIN-93M diet containing high fat (18% w/w) with low protein (10% w/w). After four weeks, the rats were divided into four groups (n = 8/group) and fed experimental diets with different nitrogen sources and levels, respectively; 10% soy protein isolate (10SPI), 25% soy protein isolate (25SPI), 25% soy protein hydrolysates (25SPH) and 25% soy macro-peptide fractions (25SPP, MW≥ 10,000) for six weeks. Weight gain was significantly higher in 25% nitrogen sources-fed groups than in 10% group (10SPI). In 25SPP, perirenal fat mass and serum total lipid were significantly lower than in other groups. As for appetite-related hormones, serum ghrelin concentration was not shown to be different among groups but leptin concentration was significantly decreased in 25SPP. It can be concluded that soy macro-peptide fractions as compared with intact soy protein may have beneficial effects on reducing fat mass and serum lipid.

A Specific Blend of Intact Protein Rich in Aspartate Has Strong Postprandial Glucose Attenuating Properties in Rats

Three studies were carried out to help define an optimal protein blend for use in a nutritional product for diabetic patients. To this end, we tested the effects of coinfusions of combinations of different types of carbohydrates and proteins on the postprandial glycemic plasma response in healthy rats. Expt. 1 compared the effects of administering different forms of soy protein (intact protein, its hydrolysate, or an equivalent amount of the same amino acids), all in combination with a fixed amount of glucose (Glu), on postprandial Glu and insulin plasma concentrations. Intact soy protein (SI) had stronger insulinogenic properties compared with its hydrolysate but was equally potent in reducing the postprandial Glu response. In Expt. 2, we compared the effect of replacing 50% of the SI with the whey-derived protein α-lactalbumin when coingested with maltodextrin as the carbohydrate source. Only the specific aspartate-rich blend of SI and α-lactalbumin significantly improved the postprandial Glu response. In Expt. 3, we studied the effect of using the blend of SI and α-lactalbumin combined with a slowly digestible carbohydrate. The protein blend was still capable of significantly decreasing the postprandial Glu response even when a slow-release carbohydrate source was included. Combining this aspartate-rich protein blend with a slow-release carbohydrate might therefore lead to a low-glycemic nutritional product beneficial for dietary management in diabetic patients.

Soy Protein, Isoflavones, and Cardiovascular Health

This editorial summarizes the recent American Heart Association (AHA) Science Advisory on soy protein and isoflavones (phytoestrogens) published in the February 21, 2006, issue of Circulation .1 Soy protein and isoflavones have gained considerable attention for their potential role in improving risk factors for cardiovascular disease. This scientific advisory report assesses the more recent work published on soy protein and its component isoflavones. In 22 randomized trials, isolated soy protein with isoflavones compared with milk or other proteins decreased LDL cholesterol concentrations in most studies; the average effect was approximately 3%. This reduction is very small compared with the large amount of soy protein tested in these studies, averaging 50 g, approximately half the usual total daily protein intake. No significant effects were evident on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. Among 19 studies of soy isoflavones, the average effect on LDL cholesterol and other lipid risk factors was nil. Soy protein or isoflavones have not been shown to lessen vasomotor symptoms of menopause, and results are mixed regarding slowing of postmenopausal bone loss. The efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate are not established; evidence from clinical trials is meager and cautionary as regards a possible adverse effect. For this reason, use of isoflavone supplements in food or pills is not recommended. Thus, earlier research indicating that soy protein compared with other proteins has clinically important favorable effects has not enjoyed confirmation. In contrast, many soy products should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. In October 1999, the US Food and Drug Administration (FDA) approved labeling for foods containing soy protein as protective against coronary heart disease.2 …

Soy Protein Enhances the Cholesterol-Lowering Effect of Plant Sterol Esters in Cholesterol-Fed Hamsters

This study aimed to investigate whether the combination of plant sterol esters (PSE) with soy protein or soy isoflavones may have extra cholesterol-lowering effects. Male hamsters (n=20/group) were fed diets containing (g/100 g diet) (A) 20 casein (control), (B) 0.24 PSE, (C) 20 intact soy protein (replacing casein), (D) 0.02 soy isoflavones, (E) 0.24 PSE plus 20 soy protein (replacing casein), or (F) 0.24 PSE plus 0.02 soy isoflavones, for 5 wk. All diets contained 0.08 g cholesterol/100 g diet. Compared with the control diet, the PSE and soy protein diets significantly lowered the plasma total cholesterol concentration by 13% (P<0.05) and 9% (P<0.05), respectively, whereas the isoflavone diet (D) had no effect. The combination of PSE and soy protein (diet E) decreased plasma total cholesterol by 26% (P<0.05). The decrease in plasma cholesterol concentration was mainly in the non-HDL fraction. In addition, the combination of PSE and soy protein significantly decreased plasma triacylglycerol concentration (37%, P<0.05) and reduced cholesterol accumulation in the liver. The abundance of hepatic LDL-receptors was not influenced by any of the test diets. PSE selectively increased fecal excretion of neutral sterols by 190% (P<0.05), whereas soy protein increased fecal excretion of neutral sterols and bile acids by 66% (P<0.05) and 130% (P<0.05), respectively. The combination of PSE and soy protein increased the fecal excretion of neutral sterols and bile acids compared with PSE and soy protein alone. In conclusion, the combination of PSE and soy protein more dramatically lowers plasma lipids than the individual ingredients.

Moderate intakes of intact soy protein rich in isoflavones compared with ethanol-extracted soy protein increase HDL but do not influence transforming growth factor β1 concentrations and hemostatic risk factors for coronary heart disease in healthy subjects

Soybeans contain estrogenic isoflavones that may influence plasma concentrations of transforming growth factor beta(1) (TGF-beta(1)) and plasma lipid and hemostatic risk factors for coronary heart disease. We compared the effects of moderate intakes of soy protein containing intact phytoestrogens (high-isoflavone diet) and soy protein from which most of the phytoestrogens had been extracted (low-isoflavone diet) on active TGF-beta(1) concentrations and plasma lipid and hemostatic risk factors for coronary heart disease. A randomized crossover trial was conducted in 22 young, healthy, normolipidemic subjects (5 men and 17 women) who consumed diets providing 56 or 2 mg isoflavones/d for 17 d each with a 25-d washout period between treatments. Fasting blood samples were obtained on days 13 and 14 of each treatment to measure plasma isoflavone, lipid, fibrinogen, and active TGF-beta(1) concentrations and factor VII coagulant and plasminogen activator inhibitor type 1 activities. Plasma isoflavone concentrations were 100-999 times greater after the high-isoflavone diet than after the low-isoflavone diet (P < 0.05). Plasma HDL-cholesterol and apolipoprotein A-I concentrations were 4% (95% CI: 1%, 8%) and 6% (95% CI: 3%, 10%) higher, respectively, after the high-isoflavone diet than after the low-isoflavone diet (P < 0.01 for both). Compared with soy protein from which most of the phytoestrogens have been extracted, soy protein with intact phytoestrogens increases HDL-cholesterol and apolipoprotein A-I concentrations but does not influence LDL-cholesterol, TGF-beta(1), or fibrinogen concentrations; factor VII coagulant activity; or plasminogen activator inhibitor type 1 activity in normolipidemic, healthy subjects.

The Inhibitory Effect of Soy Protein Isolate on Atherosclerosis in Mice Does Not Require the Presence of LDL Receptors or Alteration of Plasma Lipoproteins

The mechanisms by which dietary soy favorably influences lipoprotein metabolism and inhibits atherosclerosis are uncertain. Studies of blood mononuclear cells and cultured hepatocytes have indicated that certain soy peptides (i.e., 7S globulins) stimulate expression of LDL receptors. This pathway represents a hypothetical mechanism by which soy's hypocholesterolemic and antiatherosclerotic effects may be mediated. However, direct evidence supporting this hypothesis is lacking. To address this, we compared effects of dietary soy protein isolate in two genetically engineered mouse models of atherosclerosis. One mouse [LDL receptor -/- + apolipoprotein (apo) B transgenic] is devoid of LDL receptors and overproduces apolipoprotein B, whereas the other (apoE -/-) has a normal complement of LDL receptors but does not produce apolipoprotein E. Male (n = 10-12/group) and ovariectomized female (n = 10-12/group) mice were studied. There were three treatment groups, which differed principally by the source of the protein component of the diet: 1) casein/lactalbumin (no isoflavones), 2) alcohol-washed soy protein isolate (total isoflavones = 0.04 mg/g), and 3) intact soy protein isolate (total isoflavones = 1.72 mg/g). Atherosclerosis was assessed by quantifying the aortic content of esterified cholesterol. Atherosclerosis was inhibited (relative to the casein/lactalbumin group) by both alcohol-washed (45 and 31%) (P < 0.05) and intact (65 and 41%) (P < 0.05) soy protein isolate in LDL receptor -/- and apoE -/- mice, respectively. There was no sex difference. In a two-way analysis, there were significant effects of type of soy isolate and type of mouse. The antiatherosclerosis effect was enhanced in LDL receptor -/- mice (P < 0.001) and diminished in mice fed alcohol-washed soy protein isolate (P < 0.001). Furthermore, inhibitory effects of soy on atherosclerosis were unrelated to plasma LDL, VLDL or HDL cholesterol concentrations. The results represent direct evidence for the existence of LDL receptor- and plasma lipoprotein-independent pathways by which dietary soy protein isolate inhibits atherosclerosis.

The Use of Herbal and Botanical Therapies in Menopause

Botanical supplements and medicines have been used for centuries to treat menopausal symptoms. Although scientific data on these remedies are limited, their current popularity is rooted in the naive hope that so-called plant-based estrogens, phytoestrogens, or botanicals will provide all the benefits of hormone therapy (HT) without the concomitant risks for neoplasm and venous thrombosis. Plant sterol molecules are used as precursors in the manufacture of synthetic steroids, and the hormones in most prescription sex steroids are derived from diosgenin, a weakly estrogenic compound found in varieties of yams and in soy. Plant sterols interact with estrogen receptors and should be thought of as selective estrogen-receptor modulators (SERMs, more correctly termed phyto-SERMs) rather than as phytoestrogens. Generally, the receptor interactions of phyto-SERMs do not induce activity of intensity equal to that of mammalian estrogens. Botanical substances commonly thought to be estrogenic include soy, black cohosh, evening primrose oil, dong quai, ginseng, red clover, and members of the dill family. Intact soy protein with active isoflavones (i.e., genistein and daidzein) appears to …

Incorporating soy protein into a low-fat, low-cholesterol diet.

The US Food and Drug Administration recommends including four servings of at least 6.25 g each (25 g/day) of soy protein into a diet low in saturated fat and cholesterol to reduce the risk of heart disease. Patients are more likely to comply with this dietary change if they have their physician's support. The author discusses how the clinician can help patients incorporate soy protein into a low-cholesterol, low-fat diet. A meta-analysis found that soy protein consumption achieved an average 9.3% decrease in total cholesterol, a 12.9% decrease in low-density lipoprotein (LDL) cholesterol, and a 10.5% decrease in triglycerides. Soy pills and supplements such as isoflavone are not recommended. The cholesterol-lowering benefit has only been observed when the intact soy protein is used. Soy milk can be used in place of milk in coffee or over breakfast cereal, as well as in milkshakes and other blended drinks. Soy milk can be substituted for milk in many recipes.

Effect of intact and isoflavone-depleted soy protein on NMU-induced rat mammary tumorigenesis.

Experiments in animal models of carcinogenesis suggest that soy consumption decreases tumor number and incidence. Genistein, an isoflavone which is present in soy at high concentrations, has been considered to be the primary antitumor constituent in soy. In the present study, the N-nitroso-N-methylurea (NMU)-induced mammary tumor model was used as a means to determine whether the chemopreventive effect of soy was attributable specifically to its high content of isoflavones. Five groups of rats (30/group) were fed the following modified AIN-93G diets: group 1, 20% intact soy protein (SP); group 2, 10% SP; group 3, 20% isoflavone-depleted soy protein (IDSP); group 4, 10% IDSP; group 5, the casein-based AIN-93G diet. The SP contained 1.07 and IDSP 0.073 mg genistein/g isolate, respectively. Experimental diets were initiated 1 week prior to NMU administration (at 50 days of age) and continued for another 18 weeks. No significant differences were found among the five groups when assessed in terms of tumor incidence, latency, multiplicity or volume. A trend towards inhibition was observed in both the 20 and 10% SP and IDSP groups when assessed in terms of total tumors/group, tumor volume and latency, but this trend did not achieve statistical significance. The results of this model study do not support the hypothesis that the isoflavone components of soy protein, or soy protein itself, inhibit chemically induced mammary tumor development.

Consumption of Soy Protein Reduces Cholesterol Absorption Compared to Casein Protein Alone or Supplemented with an Isoflavone Extract or Conjugated Equine Estrogen in Ovariectomized Cynomolgus Monkeys

Dietary intake of soy protein is associated with reductions in plasma cholesterol. Isoflavones are thought to be active components of soy and responsible for the beneficial effects because of their structural similarities to estrogen. The purposes of this study were to determine if i) soy protein or a semipurified soy extract, rich in isoflavones, is responsible for improving the lipid profile and ii) altered intestinal cholesterol metabolism is one mechanism for hypocholesterolemic effects. Ovariectomized adult female cynomolgus monkeys (40) were assigned to groups fed diets containing i) casein-lactalbumin (CAS) ii) intact soy protein (SOY), iii) CAS plus an isoflavone-rich semipurified soy extract similar in isoflavone content as SOY (ISO) or iv) CAS plus conjugated equine estrogen (CEE) for 20 wk. Cholesterol absorption was determined using the fecal isotope ratio method. Bile acid excretion was measured using the 3alpha-hydroxysteroid dehydrogenase assay. The SOY group had significantly lower total- and VLDL + LDL-cholesterol compared to the other three groups and significantly higher HDL-cholesterol compared to the CAS and CEE groups. Cholesterol absorption was significantly lower in the SOY group compared to the other groups, but bile acid excretion was not significantly affected. The hypocholesterolemic effect of soy protein appears to be mediated in part by decreased cholesterol absorption. The semipurified soy extract, rich in isoflavones, added to casein protein did not have lipid-lowering effects. Other components of soy such as saponins, phytic acid or the amino acid composition may be involved in the hypocholesterolemic effects seen in this study.

Intact Dietary Soy Protein, but Not Adding an Isoflavone-Rich Soy Extract to Casein, Improves Plasma Lipids in Ovariectomized Cynomolgus Monkeys

The dietary consumption of soy protein has been linked to a reduction in coronary heart disease and improvements in a number of related risk factors. Recent investigations have focused on isoflavone components of soy protein. The purpose of this study was to examine plasma lipids and lipoproteins, particularly LDL, with the intake of intact soy protein or casein-lactalbumin diets with and without a semipurified extract of soy, rich in isoflavones. Sixty ovariectomized cynomolgus monkeys were assigned to one of three groups fed diets containing the following: 1) casein-lactalbumin as the protein source (CAS; n = 20); 2) CAS plus a semipurified extract of soy, rich in isoflavones (ISO; n = 20); or 3) intact soy protein (SOY; n = 20) for 12 wk. Lipoproteins were fractionated by combined ultracentrifugation and HPLC. Isolated LDL particles were further subfractionated by dividing the LDL peak into three fractions for compositional analyses. The SOY group had significantly lower plasma total cholesterol, VLDL plus IDL cholesterol and LDL cholesterol, and significantly less HDL cholesterol than the CAS group. LDL particles from the SOY group had a significantly less cholesteryl ester than the CAS group. The semipurified extract of soy, rich in isoflavones, added to casein-lactalbumin protein did not have the same effects as intact soy protein on plasma lipids and lipoproteins. Other components of soy protein, either alone or in combination with isoflavones, may be involved in the effects seen in this study.

Phytoestrogen and Intact Soy Protein Consumption Differ in Their Effects on Plasma Lipids and Lipoproteins

Phytoestrogen and Intact Soy Protein Consumption Differ in Their Effects on Plasma Lipids and Lipoproteins

Intestinal Transit and Absorption of Soy Protein In Dogs Depend On Load and Degree of Protein Hydrolysis

Soy protein, in both intact and hydrolyzed forms, is widely used as the nitrogen source in infant and adult formulas. This protein is also consumed in vast quantities worldwide as soybean-based food products. Digestion is the rate-limiting step in the assimilation of proteins from the gut. As a result, intestinal transit must be slowed when a higher load of protein is available or when this nutrient is delivered in the intact rather than hydrolyzed form. However, little information is available on the effect of load and degree of hydrolysis of soy protein on intestinal transit and protein absorption. To test the hypothesis that inhibition of intestinal transit and protein absorption depend on the load of soy protein and the state of hydrolysis of this nutrient, we compared intestinal transit and protein absorption in dogs equipped with duodenal and midintestinal fistulas during intestinal perfusion with 0, 50, 100, or 200 g/L solutions of intact soy protein versus 0, 100, 200, 300, or 400 g/L solutions of hydrolyzed soy protein. We found that intestinal transit was slowed in a load-dependent fashion by intact (P< 0.001) and hydrolyzed (P< 0.05) soy protein. Soy protein inhibited intestinal transit more potently in the intact than hydrolyzed form (P< 0.05). A greater amount of protein was absorbed by the proximal half of the small intestine when soy protein was delivered in the hydrolyzed than intact form (P< 0.05), and the efficiency of protein absorption was maintained at a high and nearly constant level of 82.6 to 87.4% for intact soy protein and 89.0 to 92.3% for hydrolyzed soy protein. We conclude that in dogs intestinal transit and absorption of soy protein depend on the load and the degree of protein hydrolysis.