Soy ploy

  RATIONALE. Most commercial rodent diets are formulated with soya protein and therefore contain soya isoflavones. Isoflavones form one of the main classes of phytoestrogens and have been found to exert both oestrogenic and anti-oestrogenic effects on the central nervous system. The effects have not been limited to reproductive behaviour, but include effects on learning and anxiety and actions on the hypothalamo-pituitary axis. It is therefore possible that the soya content of diet could have significant effects on brain and behaviour and be an important source of between-laboratory variability.
  OBJECTIVES. To determine whether behaviour in two animal tests of anxiety, and stress hormone production, would differ between rats that were fed a diet which was free of soya isoflavones and other phytoestrogens (iso-free) and those that were fed a diet which contained 150 &mgr;g/g [sic] of the isoflavones genistein and daidzein (iso-150). This controlled diet has an isoflavone concentration similar to that in the maintenance diet routinely used in our institution.
  METHODS. Male rats were randomly allocated to the iso-free and iso-150 diets and their body weights and food and water consumption were recorded for 14 days. They were then maintained on the same diets, but housed singly for 4 days, before testing in the social interaction and elevated plus-maze tests of anxiety. Corticosterone concentrations in both dietary groups were determined under basal conditions and after the stress of the two tests of anxiety. Vasopressin and oxytocin concentrations were determined after brief handling stress.
  RESULTS. The groups did not differ in food or water intake, body weight or oxytocin concentrations. Compared with the rats fed the iso-free diet, the rats fed the iso-150 diet spent significantly less time in active social interaction and made a significantly lower percentage of entries onto the open arms of the plus-maze, indicating anxiogenic effects in both animal tests. The groups did not differ in their basal corticosterone concentrations, but the iso-150 group had significantly elevated stress-induced corticosterone concentrations. Stress-induced plasma vasopressin concentrations were also significantly elevated in the iso-150 diet group compared with the iso-free rats.
  CONCLUSIONS. Major changes in behavioural measures of anxiety and in stress hormones can result from the soya isoflavone content of rat diet. These changes are as striking as those seen following drug administration and could form an important source of variation between laboratories.

PMID: 12618915

  OBJECTIVE:: We examined the effects on serum sex steroids, lipids and markers of oxidative stress of supplementing the diets of healthy male volunteers with scones made with soya flour.
  DESIGN:: A randomized placebo controlled cross-over trial.
  SETTING:: University Hospital of Wales.
  SUBJECTS:: Twenty volunteers recruited by advertisement.
  INTERVENTIONS:: Male volunteers ate three scones a day in addition to their normal diet for a period of 6 weeks. The scones were made with either wheat or soya flour (containing 120 mg/day of isoflavones). Blood was analysed for sex steroids (testosterone, dihydro-testosterone, oestradiol, oestrone, sex hormone binding globulin, albumin and the concentration of non-protein bound sex steroids were calculated), lipid profile (total cholesterol, high density lipoprotein cholesterol and triglycerides) and measures of oxidative stress (hydroperoxides, susceptibility of LDL to oxidation with copper and myeloperoxidase).
  RESULTS:: The volunteers' mean age was 35.6 (s.d. 11.2) y. Total serum testosterone fell in volunteers taking the soya scones (19.3-18.2 nmol/l; 95% CI 1.01, 1.12; P=0.03). No significant changes were seen in the concentrations of the other serum sex steroids, albumin or sex hormone binding globulin throughout the study. Significant improvements in two of the three markers of oxidative stress were seen in volunteers taking soya scones. Lag time for myeloperoxidase rose from 55.0 to 68.0 min (95% CI -16.0, -3.5; P=0.009) and the presence of hydroperoxides decreased from 2.69 to 2.34 micro mol/l (95% CI 0.12, 0.71; P=0.009). There were no changes seen in serum triglycerides or cholesterol.
  CONCLUSIONS:: We have shown that soya supplements reduce serum testosterone and improve markers of oxidative stress. These findings provide a putative mechanism by which soya supplements could protect against prostatic disease and atherosclerosis. Further dietary studies with clinical end points are warranted.
  SPONSORSHIP:: The Mason medical research foundation.European Journal of Clinical Nutrition (2003) 57, 100-106. doi:10.1038/sj.ejcn.1601495

[So, does eating soy products lead to male homosexuality? - ljf]

PMID: 12548304

  Genistein, a soy isoflavone, has in vitro immunosuppressive properties. [Suppressing the immunological system so it can not protect the organism is not a good idea! - ljf] We investigated whether genistein or dietary soy protein containing isoflavones could influence the outcome of rat cardiac allografts. Lewis rats were fed a diet with protein from high isoflavone soy protein fraction (HIS), casein (CAS) or casein with isoflavones added (CI) starting 1 wk before heart transplants from Wistar Furth donors, and continuing throughout the study. HIS-fed rats had significantly prolonged time to rejection compared with CAS- and CI-fed recipients (10.8 +/- 2.62 vs. 7.18 +/- 0.75 and 7.22 +/- 0.44 d, P < 0.001). Intravenous genistein [20mg/(kg. d) for 14 d] significantly prolonged heart survival compared with controls and dissolvent-treated recipients (23.2 +/- 7.4 vs. 8.4 +/- 1.3 and 11.4+/3.6 d, P < 0.0005), and had an additive effect when given to heart recipients also receiving low dose cyclosporine for 7 d (30.8 +/- 2.3 vs. 23.4 +/- 2.4 d, P < 0.005). Concanavalin A-stimulated lymphocytes, isolated from Lewis rats given intraperitoneal genistein for 7 d, had decreased production of interferon gamma compared with controls or dimethyl sulfoxide-treated groups (22.6 +/- 9.9 vs 149 +/- 105 and 154 +/- 103 micro g/L, P < 0.05). In conclusion, a high isoflavone soy diet and intravenous genistein, but not isoflavone extract alone, delay rejection of rat cardiac allografts, with an additive effect in cyclosporine-treated rats. In addition, intraperitoneal genistein has immunosuppressive properties in vivo.

PMID: 12163676

  For many years soy bean-based formulas (SBBF) were the only dietary product used for infants with cow's milk intolerance. At the present time, their place in infant nutrition is reduced as a result of the availability of new dietary products without lactose and/or cow's milk proteins and the recognition of soy bean protein allergy. There is no evidence that SBBF have any efficiency in infant colic. SBBF have no indication in the prevention of allergy, nor in premature infants' nutrition. Their main indication is the feeding of infants of vegetarian parents who do not want to use cow's milk products. Studies have shown that SBBF contain large quantities of phytoestrogens, particularly isoflavone. Because of experimental data suggesting a possible deleterious effect of phytoestrogens on the neuroendocrine maturation, the reduction of their content in SBBF must be considered.

PMID: 11760676

  Genistein, the principal soy isoflavone, has estrogenic activity and is widely consumed by humans for putative beneficial health effects. The goal of the present study was to measure placental transfer of genistein in rats as a possible route of developmental exposure. Pregnant Sprague-Dawley rats were administered genistein orally, either by diet or by gavage. Concentrations of genistein aglycone and conjugates were measured in maternal and offspring serum and brain using HPLC with isotope dilution electrospray tandem mass spectrometry. Although fetal or neonatal serum concentrations of total genistein were approximately 20-fold lower than maternal serum concentrations, the biologically active genistein aglycone concentration was only 5-fold lower. Fetal brain contained predominately genistein aglycone at levels similar to those in the maternal brain. These studies show that genistein aglycone crosses the rat placenta and can reach fetal brain from maternal serum genistein levels that are relevant to those observed in humans.

PMID: 11297868

  Diets with protein of inferior quality may increase protein breakdown in skeletal muscle but the experimental results are inconsistent. To elucidate the relationship, pigs were fed isoenergetic and isonitrogenous diets based on soyabean-protein isolate or casein for 15 weeks, with four to six animals per group. A higher plasma level of urea (2.5-fold the casein group value, P = 0.01), higher urinary N excretion (2.1-fold the casein group value, P = 0.01), a postabsorptive rise in the plasma levels of urea, 3-methylhistidine and isoleucine in soyabean protein-fed pigs suggested recruitment of circulatory amino acids by protein breakdown in peripheral tissues. Significant differences between dietary groups were detected in lysosomal and ATP-dependent proteolytic activities in the semimembranosus muscle of food-deprived pigs. A higher concentration of cathepsin B protein was found, corresponding to a rise in the cathepsin B activity, in response to dietary soyabean protein. Muscle ATP-stimulated proteolytical activity was 1.6-fold the casein group value (P = 0.03). A transient rise in the level of cortisol (2.9-times the casein group value, P = 0.02) occurred in the postprandial phase only in the soyabean group. These data suggest that the inferior quality of dietary soyabean protein induces hormonally-mediated upregulation of muscle protein breakdown for recruitment of circulatory amino acids in a postabsorptive state.

PMID: 11348559

  Phytoestrogens are extensively investigated for their potential to prevent many hormone-dependent cancers and age-related diseases, however little is known about their effects in brain. Brain aromatase and plasma phytoestrogen levels were determined in Sprague-Dawley rats fed a phytoestrogen-rich diet during pregnancy/lactation. Ingested phytoestrogens cross the placenta and become concentrated in maternal milk as evident from high infantile plasma concentrations. Dietary phytoestrogens, however, do not alter brain aromatase during pregnancy/lactation or perinatal development.

PMID: 11248356

  OBJECTIVE: To examine associations of midlife tofu consumption with brain function and structural changes in late life. METHODS: The design utilized surviving participants of a longitudinal study established in 1965 for research on heart disease, stroke, and cancer. Information on consumption of selected foods was available from standardized interviews conducted 1965-1967 and 1971-1974. A 4-level composite intake index defined "low-low" consumption as fewer than two servings of tofu per week in 1965 and no tofu in the prior week in 1971. Men who reported two or more servings per week at both interviews were defined as "high-high" consumers. Intermediate or less consistent "low" and "high" consumption levels were also defined. Cognitive functioning was tested at the 1991-1993 examination, when participants were aged 71 to 93 years (n = 3734). Brain atrophy was assessed using neuroimage (n = 574) and autopsy (n = 290) information. Cognitive function data were also analyzed for wives of a sample of study participants (n = 502) who had been living with the participants at the time of their dietary interviews. RESULTS: Poor cognitive test performance, enlargement of ventricles and low brain weight were each significantly and independently associated with higher midlife tofu consumption. A similar association of midlife tofu intake with poor late life cognitive test scores was also observed among wives of cohort members, using the husband's answers to food frequency questions as proxy for the wife's consumption. Statistically significant associations were consistently demonstrated in linear and logistic multivariate regression models. Odds ratios comparing endpoints among "high-high" with "low-low" consumers were mostly in the range of 1.6 to 2.0. CONCLUSIONS: In this population, higher midlife tofu consumption was independently associated with indicators of cognitive impairment and brain atrophy in late life.

PMID: 10763906

  The iron status of young Chinese Buddhist vegetarians (23 men and 32 women) and nonvegetarian students (20 men and 39 women from a medical college) was investigated by dietary assessment of iron intake and hematological measurement of biochemical indices including hemoglobin, plasma iron, transferrin, transferrin saturation and plasma ferritin. A characteristic of the vegetarian diet in this study was the replacement of meat by soybean products. Results of the dietary assessment showed that the average iron density of the diets ranged from 1.9 to 2.2 mg/MJ, with no difference between the vegetarian and nonvegetarian diets. Daily iron intake was similar in both vegetarian and nonvegetarian men. However, iron intake was significantly higher in female vegetarians than nonvegetarians, averaging 104 and 78% of the RDA, respectively. Results of blood analysis showed that, for both sexes, the median plasma ferritin concentration of the vegetarians (male 47 micrograms/L and female 12 micrograms/L) was about half the level of the nonvegetarians (male 91 micrograms/L and female 27 micrograms/L). Occurrence and risk of iron deficiency are more prevalent in vegetarians. Correlation between plasma ferritin concentration and years of vegetarian practice in vegetarian men was marginally significant (r = -0.38, P = 0.077). We conclude that a vegetarian diet that is rich in soybean products and restricted in animal foods is limited in bioavailable iron and is not adequate for maintaining iron balance in men and women.

PMID: 7861248

  Previous work has shown that exposure of developing rats to soy lecithin preparations (SLP) influences macromolecular constituents of immature brain cells and causes abnormal behavioral patterns. To determine if synaptic mechanisms are adversely affected by SLP, we examined the developmental characteristics of noradrenergic and dopaminergic pathways in discrete brain regions. Although transmitter levels were unaffected, the utilization rates of both catecholamines were profoundly disturbed in an age-dependent, regionally-selective manner. Utilization tended to be subnormal in the preweanling stage, but demonstrated a postweaning elevation in cerebellum and midbrain + brainstem. Enhanced utilization persisted in the latter region only, and cerebral cortex actually showed a lowered utilization rate in adulthood (60 days of age). Transmitter uptake capabilities were also affected by developmental exposure to SLP, as was tyrosine hydroxylase activity. The patterns of effects on these two variables indicated that the altered transmitter utilization rate probably reflected a change in impulse activity in the affected neuron populations, with promotion of activity in the midbrain + brainstem and reduced activity in the cerebral cortex. These data indicate that dietary supplementation with SLP throughout perinatal development alters synaptic characteristics in a manner consistent with disturbances in neural function.

PMID: 2876756