Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials

BACKGROUND: Clinical trials have reported the cholesterol-lowering effects of soy protein intake, but the components responsible are not known. OBJECTIVE: This meta-analysis was primarily conducted to evaluate the precise effects of soy isoflavones on lipid profiles. The effects of soy protein that contains enriched and depleted isoflavones were also examined. DESIGN: PUBMED was searched for English-language reports of randomized controlled trials published from 1990 to 2006 that described the effects of soy protein intake in humans. Eleven studies were selected for the meta-analysis. RESULTS: Soy isoflavones significantly decreased serum total cholesterol by 0.10 mmol/L (3.9 mg/dL or 1.77%; P = 0.02) and LDL cholesterol by 0.13 mmol/L (5.0 mg/dL or 3.58%; P < 0.0001); no significant changes in HDL cholesterol and triacylglycerol were found. Isoflavone-depleted soy protein significantly decreased LDL cholesterol by 0.10 mmol/L (3.9 mg/dL or 2.77%; P = 0.03). Soy protein that contained enriched isoflavones significantly decreased LDL cholesterol by 0.18 mmol/L (7.0 mg/dL or 4.98%; P < 0.0001) and significantly increased HDL cholesterol by 0.04 mmol/L (1.6 mg/dL or 3.00%; P = 0.05). The reductions in LDL cholesterol were larger in the hypercholesterolemic subcategory than in the normocholesterolemic subcategory, but no significant linear correlations were observed between reductions and the starting values. No significant linear correlations were found between reductions in LDL cholesterol and soy protein ingestion or isoflavone intakes. CONCLUSIONS: Soy isoflavones significantly reduced serum total and LDL cholesterol but did not change HDL cholesterol and triacylglycerol. Soy protein that contained enriched or depleted isoflavones also significantly improved lipid profiles. Reductions in LDL cholesterol were larger in hypercholesterolemic than in normocholesterolemic subjects.     

大豆异黄酮摄入显著抑制女性骨丢失:随机对照研究的meta分析

目的采用meta分析方法研究大豆异黄酮摄入对骨丢失影响。方法搜索MEDLINE、中国期刊网等中外数据库,收集了考察大豆异黄酮摄入与尿脱氧吡啶酚(Dpyr)、血清骨特异性碱性磷酸酶(BAP)、脊椎骨骨密度(SBMD)相关的随机对照研究,并对符合纳入标准的研究进行了meta分析。结果纳入18篇研究,978个研究对象。与对照组相比,大豆异黄酮组尿Dpyr的浓度显著降低,其效应值为-2.08nmol/mmol(95%CI:-3.82～0.34);血清BAP的浓度显著升高了1.48μg/L(95%CI:0.22,2.75),大豆异黄酮摄入组SBMD显著增加了20.6mg/cm2(95%CI:4.5～36.6)。当大豆异黄酮摄入量大于90mg/d或持续时间6个月时,对SBMD的影响效应值分别为28.5mg/cm2(95%CI:8.4～48.6)和27mg/cm2(95%CI:8.3～45.8)。结论大豆异黄酮干预能显著地抑制骨吸收和刺激骨形成,从而改善骨质量,防止妇女骨质疏松的发生。     

Effect of soy protein varying in isoflavone content on serum lipids in healthy young men

BACKGROUND: Previous research supports a role for soy protein in reducing serum lipids; however, few studies involved healthy male subjects or focused on soy isoflavones (or did both). OBJECTIVE: The objective was to ascertain the effects of soy protein varying in isoflavone content on serum lipids in healthy young men. DESIGN: Thirty-five males (x +/- SD age: 27.9 +/- 5.7 y) consumed milk protein isolate (MPI), low-isoflavone soy protein isolate (low-iso SPI; 1.64 +/- 0.19 mg aglycone isoflavones/d), and high-isoflavone SPI (high-iso SPI; 61.7 +/- 7.4 mg aglycone isoflavones/d) for 57 d each, separated by 4-wk washout periods, in a randomized crossover design. Blood samples were collected at the beginning and end of each treatment period, and total, LDL, and HDL cholesterol; triacylglycerols; apolipoprotein (apo) B; apo A-I; and C-reactive protein (CRP) were measured in serum. Twenty-four-hour urine samples were collected for 3 consecutive days at the end of each treatment period and analyzed for isoflavones. RESULTS: Urinary isoflavones were significantly greater with consumption of the high-iso SPI than with that of the low-iso SPI or MPI. The differences between the 3 treatments with respect to individual serum lipids were not significant, but the ratios of total to HDL cholesterol, LDL to HDL cholesterol, and apo B to apo A-I were significantly lower with both SPI treatments than with MPI treatment. CONCLUSION: Soy protein, regardless of isoflavone content, modulates serum lipid ratios in a direction beneficial for cardiovascular disease risk in healthy young men.     

Relation between soy-associated isoflavones and LDL and HDL cholesterol concentrations in humans: a meta-analysis

BACKGROUND: Differences in isoflavone content of soy protein may explain the absence of a dose-response relation between soy protein intake and blood cholesterol concentrations. OBJECTIVE: To study specifically the effect of soy-associated isoflavones on cholesterol concentrations in well-controlled trials substituting soy protein with dairy or animal protein. DESIGN: Studies were identified by MEDLINE searches (1995 - 6 June 2002) and reviewing reference lists. Studies were included if they had a control group or treatment, experimental diets only differed in the amounts of soy protein and isoflavones and were each fed for at least 14 days. A total of 10 studies met these criteria, providing 21 dietary comparisons. SUBJECTS:: Studies comprised 959 subjects (336 men and 623 women), average age ranged from 41 to 67 y and baseline cholesterol concentration from 5.42 to 6.60 mmol/l. INTERVENTIONS: The intake of soy-associated isoflavones increased by 1-95 mg/day and the intake of soy protein increased by 19-60 g/day. RESULTS: Feeding daily 36 g soy protein with 52 mg soy-associated isoflavones on average decreased low-density lipoprotein (LDL) cholesterol by -0.17+/-0.04 mmol/l (mean+/-s.e.) and increased high-density lipoprotein (HDL) cholesterol by 0.03+/-0.01 mmol/l. There was no dose-response relation between soy-associated isoflavones and changes in LDL cholesterol (R=-0.33, P=0.14) (Pearson correlation coefficient) or HDL cholesterol (R=-0.07, P=0.76) or their ratio. CONCLUSIONS: Consumption of soy-associated isoflavones is not related to changes in LDL or HDL cholesterol.     

Plasma antioxidant capacity in response to diets high in soy or animal protein with or without isoflavones

BACKGROUND: Several clinical trials have suggested that soy intake decreases oxidative stress. Soy isoflavones have antioxidant properties in vitro, but results of supplementation in clinical trials are inconclusive. OBJECTIVE: The objective was to evaluate the independent effects of soy protein and soy-derived isoflavones on plasma antioxidant capacity and biomarkers of oxidative stress. DESIGN: Forty-two hypercholesterolemic (LDL cholesterol > 3.36 mmol/L) subjects aged >50 y were provided with each of 4 diets in random order in a crossover design. Diets varied in protein source (10% of energy, soy or animal) and isoflavone content (trace or 50 mg/1000 kcal) and were consumed for 42 d each. Plasma antioxidants, protein carbonyls, malondialdehyde, total antioxidant performance, LDL oxidizability, and urinary F(2)-isoprostanes were measured at the end of each dietary phase. RESULTS: Plasma antioxidant concentrations were not significantly different, regardless of dietary treatment, except for isoflavones, which were higher after isoflavone supplementation (P = 0.0001). Although plasma total antioxidant performance was 10% higher with soy protein intake, regardless of dietary isoflavones (P = 0.0003), soy protein did not significantly affect most individual markers of oxidative stress (LDL oxidizability, urinary F(2)-isoprostanes, malondialdehyde, or protein carbonyls in native plasma). However, soy protein was associated with modestly lower concentrations of protein carbonyls in oxidized plasma. There was no significant effect of isoflavones on LDL oxidation, urinary F(2)-isoprostanes, or protein carbonyl groups, although, paradoxically, the plasma malondialdehyde concentration was significantly higher after the isoflavone-rich diets (P = 0.04). CONCLUSIONS: Diets relatively high in soy protein or soy-derived isoflavones have little effect on plasma antioxidant capacity and biomarkers of oxidative stress.     

Soy protein favorably affects LDL size independently of isoflavones in hypercholesterolemic men and women

We assessed the independent effect of soy protein relative to animal protein and of isoflavones on various electrophoretic characteristics of LDL particles. LDL particles were characterized by polyacrylamide gradient gel electrophoresis in 36 moderately hypercholesterolemic men and women (LDL cholesterol > 3.36 mmol/L). All subjects consumed in random order each of the four diets (soy protein depleted of isoflavones, soy protein enriched in isoflavones, animal protein with no added isoflavones, and animal protein with added isoflavones) for 6 wk. Consumption of soy protein was associated with a larger LDL peak particle size relative to animal protein (P < 0.01). Soy protein also decreased the cholesterol levels in LDL < 25.5 nm by 12.3% (P < 0.001) and increased cholesterol levels in LDL > 26.0 nm by 14.3% (P < 0.05) relative to animal protein. Isoflavones did not affect these LDL particle characteristics. Soy protein shifted LDL particle distribution to a less atherogenic pattern and this effect is independent of soy's isoflavone component.     

Meta-analysis of the effects of soy protein containing isoflavones on the lipid profile

BACKGROUND: Convincing evidence shows that soy protein intake has beneficial effects on lipid changes, but it is unclear which components of soy protein are responsible. OBJECTIVE: We conducted a meta-analysis to identify and quantify the effects of soy protein containing isoflavones on the lipid profile. DESIGN: Twenty-three eligible randomized controlled trials published from 1995 to 2002 were identified from the PUBMED database (National Library of Medicine, Bethesda, MD). Weighted mean effect sizes were calculated for net changes in serum lipid concentrations by using fixed-effect or random-effect models. Pre-specified subgroup analyses were performed to explore the influence of covariates on net lipid change. RESULTS: Soy protein with isoflavones intact was associated with significant decreases in serum total cholesterol (by 0.22 mmol/L, or 3.77%), LDL cholesterol (by 0.21 mmol/L, or 5.25%), and triacylglycerols (by 0.10 mmol/L, or 7.27%) and significant increases in serum HDL cholesterol (by 0.04 mmol/L, or 3.03%). The reductions in total and LDL cholesterol were larger in men than in women. Initial total cholesterol concentrations had a powerful effect on changes in total and HDL cholesterol, especially in subjects with hypercholesterolemia. Studies with intakes >80 mg showed better effects on the lipid profile. The strongest lowering effects of soy protein containing isoflavones on total cholesterol, LDL cholesterol, and triacylglycerol occurred within the short initial period of intervention, whereas improvements in HDL cholesterol were only observed in studies of >12 wk duration. Tablets containing extracted soy isoflavones did not have a significant effect on total cholesterol reduction. CONCLUSIONS: Soy protein containing isoflavones significantly reduced serum total cholesterol, LDL cholesterol, and triacylglycerol and significantly increased HDL cholesterol, but the changes were related to the level and duration of intake and the sex and initial serum lipid concentrations of the subjects.     

Pasta naturally enriched with isoflavone aglycons from soy germ reduces serum lipids and improves markers of cardiovascular risk

Most studies of soy and cholesterol have tested foods made from purified soy proteins containing mainly isoflavone glycosides. Fermented soy foods have mainly isoflavone aglycons and account for a high proportion of the soy protein source in Asia, where there is an inverse relationship between soy intake and serum cholesterol. The aim of this study was to compare a novel soy germ pasta, naturally enriched in isoflavone aglycons as a result of the manufacturing process, with conventional pasta for effects on serum lipids and other cardiovascular risk markers. In this randomized, controlled, parallel study design of 62 adults with hypercholesterolemia who consumed a Step II diet that included one 80-g serving/d of pasta, we measured serum lipids, high sensitivity C-reactive protein (hsCRP), urinary isoprostanes, and brachial artery flow-mediated vasodilatation at baseline and after 4 and 8 wk. The pasta delivered 33 mg of isoflavones and negligible soy protein and led to a serum isoflavone concentration of 222 +/- 21 nmol/L; 69% of subjects were equol producers. Soy germ pasta reduced serum total and LDL cholesterol by 0.47 +/- 0.13 mmol/L (P = 0.001) and 0.36 +/- 0.10 mmol/L (P = 0.002) more than conventional pasta, representing reductions from baseline of 7.3% (P = 0.001) and 8.6% (P = 0.002), respectively. Arterial stiffness (P = 0.003) and hsCRP (P = 0.03) decreased and improvements in all the above risk markers were greatest in equol producers. All measures returned to baseline when patients were switched to conventional pasta. In conclusion, pasta naturally enriched with isoflavone aglycons and lacking soy protein had a significant hypocholesterolemic effect beyond a Step II diet and improved other cardiovascular risk markers.     

Soy isoflavone intake inhibits bone resorption and stimulates bone formation in menopausal women: meta-analysis of randomized controlled trials

OBJECTIVE: To clarify the effects of isoflavone intake on bone resorption and bone formation. METHODS: We identified randomized controlled trials related to urinary deoxypyridinoline (Dpyr, a bone resorption marker) and serum bone-specific alkaline phosphatase (BAP, a bone formation marker) listed on MEDLINE (January 1966-April 2006), the Cochrane Controlled Trials Register, EMBASE (1985-January 2006), Science Citation Index and PUBMED (updated till April 2006). RESULTS: Nine studies with a total of 432 subjects were selected for meta-analysis. The urinary Dpyr concentration in subjects who consumed isoflavones decreased significantly by -2.08 nmol/mmol (95% confidence interval (CI): -3.82 to -0.34 nmol/mmol) in comparison with that in subjects who did not consume isoflavones. Isoflavone intake vs placebo intake significantly increased serum BAP by 1.48 microg/l (95% CI: 0.22-2.75 mug/l). Decreases in the urinary Dpyr concentration with isoflavone intake of <90 mg/day and with treatment lasting less than 12 weeks were -2.34 nmol/mmol (95% CI: -4.46 to -0.22 nmol/mmol) and -2.03 nmol/mmol (95% CI: -3.20 to -0.85 nmol/mmol), respectively. CONCLUSIONS: Isoflavone intervention significantly inhibits bone resorption and stimulates bone formation. These favorable effects occur even if <90 mg/day of isoflavones are consumed or the intervention lasts less than 12 weeks.     

Soy isoflavones improve plasma lipids in normocholesterolemic and mildly hypercholesterolemic postmenopausal women

BACKGROUND: Soy-protein consumption is known to reduce plasma total and LDL cholesterol concentrations. However, the responsible soy component or components and the magnitude of effects in normocholesterolemic and mildly hypercholesterolemic subjects are unclear. OBJECTIVE: The present study examined the effects of soy isoflavone consumption on plasma concentrations of triacylglycerol, apolipoprotein (apo) A-I, apo B, lipoprotein(a), and total, LDL, and HDL cholesterol and on LDL peak particle diameter in normocholesterolemic and mildly hypercholesterolemic postmenopausal women. DESIGN: In a randomized crossover trial, fasting plasma samples were obtained from 18 postmenopausal women throughout three 93-d periods of daily isolated soy protein (ISP) consumption providing an average of 7.1 +/- 1.1 (control), 65 +/- 11 (low isoflavone), or 132 +/- 22 (high isoflavone) mg isoflavones/d. RESULTS: Compared with values measured during the control diet, the plasma LDL cholesterol concentration was 6.5% lower (P < 0.02) during the high-isoflavone diet and the ratio of LDL to HDL cholesterol was 8.5% and 7.7% lower during the low- and high-isoflavone diets, respectively (P < 0.02). Isoflavone consumption did not significantly affect plasma concentrations of total or HDL cholesterol, triacylglycerol, apo A-I, apo B, or lipoprotein(a) or the LDL peak particle diameter. CONCLUSIONS: Consumption of isoflavones as a constituent of ISP resulted in small but significant improvements in the lipid profile in normocholesterolemic and mildly hypercholesterolemic postmenopausal women. Although the effects were small, it is possible that isoflavones may contribute to a lower risk of coronary heart disease if consumed over many years in conjunction with other lipid-lowering strategies.     

Probiotic consumption does not enhance the cholesterol-lowering effect of soy in postmenopausal women

Numerous studies report that soy lowers cholesterol. Probiotic bacteria were also reported to lower total cholesterol (TC) and LDL cholesterol (LDL-C). We hypothesized that by altering intestinal microflora, probiotic consumption may also change phytoestrogen metabolism and enhance the effects of soy. To evaluate the independent and interactive effects of probiotic bacteria and soy on plasma TC, LDL-C, HDL cholesterol (HDL-C), and triglycerides (TG), 37 women with a baseline TC of 5.24 mmol/L were given the following 4 treatments for 6 wk each in a randomized crossover design: soy protein isolate (26 +/- 5 g soy protein containing 44 +/- 8 mg isoflavones/d); soy protein isolate + probiotic capsules (10(9) colony-forming units Lactobacillus acidophilus DDS-1 and Bifidobacterium longum); milk protein isolate (26 +/- 5 g milk protein/d); and milk protein isolate + probiotic. Soy consumption decreased plasma TC by 2.2% (P = 0.02) and LDL-C by 3.5% (P = 0.005), increased HDL-C by 4.2% (P = 0.006) and tended to decrease TG (P = 0.07) compared with milk protein intake. When divided according to initial TC concentration, soy effects were observed only in hypercholesterolemic women (TC > 5.17 mmol/L). In this subgroup, soy treatments decreased plasma TC by 3.3% (P = 0.01), LDL-C by 4.5% (P = 0.004), and TG by 10.6% (P = 0.02), and increased HDL-C by 4.2% (P = 0.02). When subjects were divided on the basis of plasma and urine concentrations of the isoflavone metabolite, equol, equol producers and nonproducers did not differ in baseline lipids or in the effects of soy. Probiotics did not lower cholesterol or enhance the effects of soy. These results confirm a beneficial effect of soy on plasma cholesterol in mildly hypercholesterolemic postmenopausal women independent of equol production status, but do not support an independent or additive effect of these particular probiotic bacteria.     

Dietary soy and soy isoflavones have gender-specific effects on plasma lipids and isoflavones in golden Syrian f(1)b hybrid hamsters

The specific components of soy responsible for its beneficial effects on plasma lipids are unknown. Golden Syrian F(1)B Hybrid hamsters (75 male, 74 female) were evaluated for the effect of dietary soy and soy isoflavones on plasma lipids. They were fed the following diets for 16 wk: casein/lactalbumin (C/L), soy protein with isoflavones [Soy(+)], soy protein with isoflavones removed [Soy(-)], Soy(-) plus isoflavone extract (IF), and C/L + IF. At necropsy, plasma total cholesterol, HDL cholesterol (HDLC), LDL + VLDL cholesterol (LDL + VLDLC), isoflavones, and uterine and accessory gland weights were measured. Male hamsters fed the three soy-containing diets had lower LDL + VLDLC concentrations than those fed the two C/L diets (P < 0.01), and those fed Soy(-) + IF did not differ from those fed Soy(+). In females, diet did not affect plasma LDL + VLDLC concentration. Females fed Soy(+) or Soy(-) had higher HDLC (P < 0.05) than those fed C/L. HDLC was not affected by diet in males. Due to higher equol production (P < 0.01), males had greater plasma isoflavone concentrations (P < 0.01) than females. There was a positive association between plasma total isoflavones and LDL + VLDLC (r = 0.65, P < 0.05) in females. These data suggest gender differences in plasma lipid and isoflavone responses to soy- based diets in Syrian F(1)B Hybrid hamsters, which offer an opportunity to explore effects of sex hormones on isoflavone metabolism and the effects of isoflavones on lipid metabolism.     

The effect of soy protein with or without isoflavones relative to milk protein on plasma lipids in hypercholesterolemic postmenopausal women

BACKGROUND: Clinical trial data and the results of a meta-analysis suggest a hypocholesterolemic effect of soy protein. The effect may be partially attributable to the isoflavones in soy. Few studies have examined the separate effects of soy protein and isoflavones. OBJECTIVE: The objective of this study was to determine the effect of soy protein and isoflavones on plasma lipid concentrations in postmenopausal, moderately hypercholesterolemic women. DESIGN: This was a randomized, double-blind, placebo-controlled clinical trial with 3 treatment groups. After a 4-wk run-in phase during which the women consumed a milk protein supplement, the subjects were randomly assigned to 12 wk of dietary protein supplementation (42 g/d) with either a milk protein (Milk group) or 1 of 2 soy proteins containing either trace amounts of isoflavones (Soy- group) or 80 mg aglycone isoflavones (Soy+ group). RESULTS: LDL-cholesterol concentrations decreased more in the Soy+ group (n = 31) than in the Soy- group (n = 33) (0.38 compared with 0.09 mmol/L; P = 0.005), but neither of these changes was significantly different from the 0.26-mmol/L decrease observed in the Milk group (n = 30). The results for total cholesterol were similar to those for LDL cholesterol. There were no significant differences in HDL-cholesterol or triacylglycerol concentrations between the 3 groups. CONCLUSIONS: The difference in total- and LDL-cholesterol lowering between the 2 soy-protein supplements suggests an effect attributable to the isoflavone-containing fraction. However, the unexpected LDL-cholesterol lowering observed in the Milk group, and the fact that there was no significant difference between either soy group and the Milk group, suggests that changes may have been due to other factors related to participation in the study.     

Modest protective effects of isoflavones from a red clover-derived dietary supplement on cardiovascular disease risk factors in perimenopausal women, and evidence of an interaction with ApoE genotype in 49-65 year-old women

Data suggest that soy protein, a source of isoflavones, may have favorable effects on cardiovascular risk factors. Women (n = 205), ages 49-65 y, were randomized into this double blind, placebo-controlled trial of 43.5 mg red clover-derived isoflavones/d. A total of 177 women completed the trial. There were no differences between treatments for changes from baseline to 12 mo in total cholesterol, LDL cholesterol, triglycerides, HDL cholesterol, systolic and diastolic blood pressures, fibrinogen, and plasminogen activator inhibitor type 1 (PAI-1) (P >/= 0.1). Interactions between treatment and menopausal status were significant for changes in triglycerides and PAI-1 (P = 0.02 and P = 0.01), and changes were significant among perimenopausal women. In the isoflavone and placebo groups, changes in triglycerides were -0.2 +/- 0.6 and 0.4 +/- 0.6 mmol/L, P = 0.02, and changes in PAI-1 were -3.06 +/- 5.88 and 4.95 +/- 6.25 IU/L, P = 0.004, respectively. Interactions between apolipoprotein E (apoE) genotype and treatment tended to be significant for changes in total and LDL cholesterol (P = 0.06 and P = 0.05), and differences between treatments were significant in E2/E3 women. In the isoflavone and placebo groups, changes in total cholesterol were -0.61 +/- 0.79 and 0.18 +/- 0.79 mmol/L, P = 0.03, and changes in LDL cholesterol were -0.84 +/- 0.79 and -0.04 +/- 0.69 mmol/L, P = 0.02, respectively. Although there were potentially beneficial changes in triglycerides and PAI-1 among perimenopausal women consuming isoflavones, this study suggests that isoflavones alone are not responsible for the well-documented effects of soy protein on blood lipids. A larger study is required to confirm the effect modification by apoE genotype.     

Soy protein isolates of varying isoflavone content exert minor effects on serum reproductive hormones in healthy young men

Inverse associations between soy and prostate cancer and the contribution of hormones to prostate cancer prompted the current study to determine whether soy protein could alter serum hormones in men. Thirty-five men consumed milk protein isolate (MPI), low-isoflavone soy protein isolate (SPI) (low-iso SPI; 1.64 +/- 0.19 mg isoflavones/d), and high-iso SPI (61.7 +/- 7.35 mg isoflavones/d) for 57 d each in a randomized crossover design. Twenty-four-hour urine samples indicated that urinary isoflavones were significantly increased by the high-iso SPI relative to the low-iso SPI and MPI. Serum collected on d 1, 29, and 57 of each treatment revealed that dihydrotestosterone (DHT) and DHT/testosterone were significantly decreased by the low-iso SPI [9.4% (P = 0.036) and 9.0% (P = 0.004), respectively] and the high-iso SPI [15% (P = 0.047) and 14% (P = 0.013), respectively], compared with the MPI at d 57. Other significant effects included a decrease in testosterone by the low-iso SPI relative to the MPI (P = 0.023) and high-iso SPI (P = 0.020) at d 29; an increase in dehydroepiandrosterone sulfate by the low-iso SPI relative to the MPI at d 29 (P = 0.001) and relative to the MPI (P = 0.0003) and high-iso SPI (P = 0.005) at d 57; and increases in estradiol and estrone by the low-iso SPI relative to the MPI at d 57 (P = 0.010 and P = 0.005, respectively). In conclusion, soy protein, regardless of isoflavone content, decreased DHT and DHT/testosterone with minor effects on other hormones, providing evidence for some effects of soy protein on hormones. The relevance of the magnitude of these effects to future prostate cancer risk requires further investigation.     

Soy protein containing isoflavones reduces the size of atherosclerotic plaques without affecting coronary artery reactivity in adult male monkeys

The cardiovascular effects of dietary soy on men or adult male experimental animals have received little attention. We determined the effects of long-term (31 mo) consumption of a commercially available soy protein concentrate containing experimentally varied concentrations of isoflavones on the development of atherosclerosis and vascular reactivity in adult male monkeys. The monkeys were fed atherogenic diets that differed only in the source of protein: Control (n = 30), casein and lactalbumin; low-isoflavone soy (n = 30), a mixture of unmodified soy protein isolate and isoflavone-depleted soy protein isolate containing 0.94 mg of isoflavones/g protein; and high-isoflavone soy (n = 31), unmodified soy protein isolate containing 1.88 mg of isoflavone/g protein. Plasma LDL cholesterol was reduced, whereas HDL cholesterol and apolipoprotein A-1 (P < 0.05) were increased in both groups that consumed soy protein. Atherosclerosis (mean plaque size in the coronary arteries) was reduced by approximately 34% (P < 0.05) in both groups fed soy protein. There were no effects of dietary soy on endothelium-dependent or -independent reactivity of coronary arteries. The results indicate that long-term consumption of soy protein containing a modest amount of isoflavones inhibits the early progression of coronary artery atherosclerosis without affecting endothelium-dependent or -independent arterial function.     

Soy food consumption does not lower LDL cholesterol in either equol or nonequol producers

BACKGROUND: Health claims link soy protein (SP) consumption, through plasma cholesterol reduction, to a decreased risk of heart disease. Soy isoflavones (ISOs), particularly in individuals who produce equol, might also contribute to lipid lowering and thus reduce SP requirements. OBJECTIVE: The objective was to examine the contributions of SP, ISOs, and equol to the hypocholesterolemic effects of soy foods. DESIGN: Nonsoy consumers (33 men, 58 women) with a plasma total cholesterol (TChol) concentration >5.5 mmol/L participated in a double-blind, placebo-controlled, crossover intervention trial. The subjects consumed 3 diets for 6 wk each in random order, which consisted of foods providing a daily dose of 1) 24 g SP and 70-80 mg ISOs (diet S); 2) 12 g SP, 12 g dairy protein (DP), and 70-80 mg ISOs (diet SD); and 3) 24 g DP without ISOs (diet D). Fasting plasma TChol, LDL cholesterol, HDL cholesterol, and triglycerides (TGs) were measured after each diet. RESULTS: TChol was 3% lower with the S diet (-0.17 +/- 0.06 mmol/L; P < 0.05) than with the D diet, and TGs were 4% lower with both the S (-0.14 +/- 0.05 mmol/L; P < 0.05) and SD (-0.12 +/- 0.05 mmol/L; P < 0.05) diets. There were no significant effects on LDL cholesterol, HDL cholesterol, or the TChol:HDL cholesterol ratio. On the basis of urinary ISOs, 30 subjects were equol producers. Lipids were not affected significantly by equol production. CONCLUSIONS: Regular consumption of foods providing 24 g SP/d from ISOs had no significant effect on plasma LDL cholesterol in mildly hypercholesterolemic subjects, regardless of equol-producing status.     

Intake of soy foods and soy isoflavones by rural adult women in China

This study evaluated the intake of soy foods and soy isoflavones by rural adult women and potential determinant factors. Soy food consumption and information on age, education and medical history were collected on 1,188 subjects in Gansu Province and Hebei Province, China using a food frequency questionnaire to gather data on food intake over the past year. Weight and height were simultaneously measured. The results showed that 1139 (95.9%) rural women consumed soy foods in the past year. The average intake of soy foods and isoflavones was 38.7 +/- 58.2 (median = 23.5) g/d and 17.7 +/- 26.6 (median= 8.9) mg/d, respectively. Tofu accounted for the most contribution to their intake. The soy isoflavone intake ranged between 0-35 mg/day in 89.2% of subjects. Gansu women had higher intakes of soy foods and isoflavones than Henbei women (P< 0.05). Women aged 41-50 years consumed less soy foods and isoflavones than the 20-30-year olds and 31-40 year olds(P < 0.05). The intake of soy foods (P< 0.01) and isoflavones (P< 0.01) by women who experienced secondary education or above was significantly higher than illiterate women. Women without a medical history had a higher soy isoflavone intake than women with a medical history, but the difference was not statistically significant. These results suggest that the intake of soy isoflavones by Chinese rural adult women was much higher than women in Western countries. The distribution of intake was skewed to the right and varied among women in regard to region, age group and education level.     

Isoflavone aglycone-rich extract without soy protein attenuates atherosclerosis development in cholesterol-fed rabbits

The antiatherogenic effect of soy protein with intact isoflavones is well established, but the effects of isoflavones without soy protein have not been determined. We investigated the antiatherogenic effect of an isoflavone aglycone-rich extract (containing 429.4 mg/g isoflavone aglycones) without soy protein from fermented soy in cholesterol-fed rabbits. We fed 12-wk-old New Zealand white male rabbits diets containing 1 g/100 g cholesterol with 0, 0.33 or 1 g/100 g isoflavone aglycones for 8 wk. We also fed the rabbits a diet containing 1 g/100 g cholesterol with 1.09 g/100 g soy saponin-rich extract, a component other than isoflavone aglycones in the isoflavone aglycone-rich extract. Controls did not consume cholesterol, isoflavone aglycones or saponins. The isoflavone aglycone- and saponin-rich extracts did not affect the serum lipid profile of cholesterol-fed rabbits. The serum concentration of daidzein in its conjugated form was significantly higher in the high isoflavone group than in the low isoflavone group. The level of cholesteryl ester hydroperoxide (ChE-OOH) induced by CuSO(4) in plasma in the high isoflavone group was significantly less than that in the cholesterol group, and the ChE-OOH levels of LDL in the low and high isoflavone groups were significantly less than those in the cholesterol group. The ChE-OOH levels in plasma and LDL in the saponin group did not differ from the cholesterol group. In the aortic arch, the cholesterol concentration was significantly lower in the high isoflavone group, and malondialdehyde concentration was significantly lower in the low and high isoflavone groups compared with the cholesterol group; however these concentrations in the saponin group did not differ from those in the cholesterol group. The atherosclerotic lesion area of the aortic arch was significantly lower in the isoflavone groups (26.3% lower in the low isoflavone group and 36.9% lower in the high isoflavone group) than in the cholesterol group. The lesion areas were not different in the soy saponin and cholesterol groups. Immunohistochemical analysis revealed fewer oxidized LDL-positive macrophage-derived foam cells in atherosclerotic lesions in the aortic arch of isoflavone groups compared with that of the cholesterol group. These results suggest that the antioxidative action of isoflavones and their antioxidative metabolites inhibit the oxidation of LDL, thereby exerting an antiatherosclerotic effect.     

Systematic review and meta-analysis of soy products consumption in patients with type 2 diabetes mellitus

Clinical trials have reported the lipid-lowering effect of consuming soy products, and epidemiological studies have shown that soy intake is associated with decreased risk of type 2 diabetes mellitus (T2DM). The aim of this meta-analysis was to systematically review the effects of soy products consumption on serum lipid profiles and glycaemic control in T2DM patients. Potential papers were initially searched from PubMed (1966 to 2010) and Cochrane Library (1984 to 2010) without language limitations. All randomized controlled trials were included in which soy products supplementation was the only intervention in subjects with type 2 diabetes. Weighted mean effect size was calculated for net changes in serum lipids and fasting glucose concentrations using fixed-effect or random-effect models. Previously defined subgroup analyses were performed to identify the source of heterogeneity. Eight studies were included according to the criteria. The intake of soy products was associated with a significant reduction in serum total cholesterol (by 0.42 mmol/L; 95% confidence interval (CI): -0.70, -0.14; p<0.001), triacylglycerol (by 0.22 mmol/L; 95% CI: -0.38, -0.07; p<0.001) and low-density lipoprotein-cholesterol (by 0.30 mmol/L; 95% CI: -0.60, -0.00; p<0.001), and a significant increase in high-density lipoprotein-cholesterol (0.05 mmol/L; 95% CI: 0.04, 0.06; p=0.89). There were no significant effects on fasting glucose, insulin and glycated hemoglobin. It can be concluded that intake of soy and soy products has beneficial effects in T2DM patients in relation to serum lipids.