Bioavailability of glycitein relatively to other soy isoflavones in healthy young Caucasian men.

Glycitein is a Selective Estradiol Receptor Modulator (SERM) from soy. The study reports plasma bioavailability and urine excretion of glycitein compared to other soy isoflavones after a unique intake of food supplement based on soy germ containing 55.24mg isoflavones. Eighteen plasma and urinary sampling profiles collected over 48h from healthy young Caucasian men were analysed using specific ELISAs. Eight profiles contained equol. Glycitein T(max), C(max), AUC(0→24h) and T(½) in plasma were calculated. Urine T(max), % of excretion at 24h and clearance were assessed. Glycitein is one of the best absorbed flavonoids. Plasma steady-state level can be achieved by several intakes a day. Glycitein bioavailability is similar to that of daidzein and its urinary excretion is significantly higher than that of genistein. Equol does not affect glycitein bioavailability. Knowing glycitein bioavailability in man is essential for the development of soy-germ-based food supplements for health applications.

Influence of ethnic origin (Asian v. Caucasian) and background diet on the bioavailability of dietary isoflavones.

Soya isoflavones: genistein and daidzein are increasingly consumed in Western countries. Their beneficial effects are discussed considering nutrition and health in Asia. The present study aimed to check whether chronic ingestions, ethnic origin and dietary context can influence soya phyto-oestrogen bioavailability. Two prospective trials were carried out to blindly assess the pharmacokinetics after acute and chronic intake of soya-based cheese (45.97 (sd1.57) mg isoflavones) taken once a day for 10 d. Twelve healthy young Asians immersed for 2 months in France were randomised in a cross-over design to compare the influence of a Western v. Asian dietary context. The second trial partly nested in the first one, compared Asians under the Western diet to twelve healthy young male Caucasians under the same diet. All volunteers were non-equol producers. After an acute intake of soya in Western diet, Asians exhibited higher maximum concentration measured in plasma (Cmax) and area under the plasma concentration-time curve (AUC) for genistein and daidzein than Caucasians (P = 0.005, 0.006, 0.032 and 0.008, respectively). In Caucasians under Western diet, AUC and Cmax values significantly increased after chronic intake. This was not the case for daidzein in Asians whatever the dietary context. For the first time, it is evidenced that on acute intake of soya cheese, Asians absorb soya phyto-oestrogens better than Caucasians, regardless of whether the background diet is Western or Asian. On chronic ingestions, AUC and Cmax values were increased for daidzein and genistein in Caucasians but not in Asians. There are ethnic differences in isoflavone pharmacokinetic and bioavailability. This may influence health outcomes.

Higher bioavailability of isoflavones after a single ingestion of a soya-based supplement than a soya-based food in young healthy males.

Soya isoflavones, genistein and daidzein, are the focus of numerous studies investigating their potential effects on health and results remain controversial. Bioavailability is clearly a crucial factor influencing their bioefficacy and could explain these discrepancies. This study aimed at assessing: (1) the isoflavone content of sixty-nine European soya-derivative products sold on the French market; (2) the bioavailability of isoflavones comparing supplement with food. Twelve healthy volunteers were recruited in a randomized two-way crossover trial and received 35 mg isoflavones equivalent aglycone either through supplements or through cheese, both containing different patterns of isoflavone conjugates and different daidzein:genistein ratios. A specific ELISA method was used to assess the plasma and urinary concentrations of isoflavones and thus the pharmacokinetic parameters, which were then normalized to mg of each isoflavone ingested. Results showed that the normalized Cmax of daidzein (P = 0.002) and similarly the normalized AUC0 --> infinity and Cmax of genistein (P = 0.002) from soya-based capsules were higher than that from soya-based cheese. In conclusion, this work completes studies on isoflavone bioavailability and presents new data regarding isoflavone concentrations in soya-derivative products. Assuming that isoflavone conjugation patterns do not influence isoflavone bioavailability, this study shows that isoflavones contained in capsules are more bioavailable than those contained in soya-based cheese. Although the supplement is more bioavailable, the relative importance of this is difficult to interpret as there is little evidence that supplements are biologically active in human subjects to date and further studies will be necessary for this specific supplement to prove its efficacy.

Endometrial safety assessment of a specific and standardized soy extract according to international guidelines.

OBJECTIVE: To assess the effects of an oral soy isoflavone extract (Phytosoya) on endometrium (evaluated by biopsy and ultrasonography) in postmenopausal women treated for 12 months. DESIGN: A total of 395 postmenopausal women were included in this international prospective, open-label study. The women were treated for 12 months with a specific standardized soy isoflavone extract (total of 70 mg/d). Endometrial biopsy and transvaginal ultrasonography were performed before and after 12 months of treatment according to European guidelines. RESULTS: A total of 301 assessable biopsy specimens were obtained from women treated for 12 months; the results were 99.67% atrophic/inactive endometrium and 0.33% proliferative endometrium. No case of hyperplasia or carcinoma was diagnosed, demonstrating the endometrial safety of this extract (point estimate: 0.0; upper limit of 95% CI: 0.012). Endometrial thickness did not show any increase after 12 months of treatment (2.2 mm at inclusion and 2.12 mm at the end of the study). Only eight women reported some kind of bleeding as an adverse event during the study. CONCLUSIONS: These results of endometrial biopsy and endometrial thickness suggest that daily administration of 70 mg of a specific and standardized isoflavone extract for 12 months does not stimulate the endometrium.

Bioavailability and urinary excretion of isoflavones in humans: effects of soy-based supplements formulation and equol production.

Soy isoflavones (IF) are of particular interest for their possible estrogenic effects on the symptoms of menopause. The bioavailability of IF is clearly a factor influencing their biological activity. The first aim of this study was to elucidate the impact of the matrix process and especially the formulation of soy-based capsules on IF bioavailability. Twelve healthy volunteers were recruited for a randomized, double-blind, two-way crossover trial and received a single dose of the two soy-based formulations, one containing a pure soy standardized extract of IF, and the other containing soy flour in addition to the standardized extract of IF. Using a new and validated ELISA method, we measured the plasma and urinary concentrations of genistein, daidzein and its metabolite equol. Based on European Medicine Evaluation Agency recommendations, the main pharmacokinetic parameters allowed us to demonstrate the bioequivalence of the two formulations, indicating that the presence or absence of soy flour did not alter either the absorption or the elimination of daidzein and genistein. As bioequivalence was demonstrated, we pooled data collected during the two study-periods to address another original issue: Did the ability to produce equol affect the bioavailability of daidzein? We demonstrated that daidzein excretion was significantly lower in equol producers compared with equol non producers over the entire elimination period of the soy IF. This difference disappeared when equol excretion was added to daidzein excretion in equol producers. Our results indicated that the production of equol could partly explain the difference in daidzein bioavailability after IF ingestion.

Effects of a standardized soy extract on hot flushes: a multicenter, double-blind, randomized, placebo-controlled study.

OBJECTIVE: To investigate the effect of an oral soy isoflavone extract (Phytosoya) on hot flushes in menopausal women. DESIGN: The study was conducted on outpatients according to a multicenter, randomized, double-blind, placebo-controlled, parallel-group design. A total of 75 patients in natural or surgical menopause suffering from at least seven hot flushes per day were randomized to receive during 4 months either soy isoflavone extract (total of 70 mg genistin and daidzin per day) or placebo. RESULTS: There is evidence to suggest that 16 weeks of treatment with soy extract can help reduce the mean number of hot flushes per 24 hours in menopausal women. Withdrawals during this trial made it difficult to obtain an unbiased estimate of the true treatment effect, but numerous sensitivity analyses lend support to the suggestion that taking soy extract can be beneficial in the treatment of hot flushes. In particular, women taking soy extract had a 38% reduction in the mean number of hot flushes by week 4 and a 51% reduction by week 8. By the end of week 16, patients taking soy extract had a 61% reduction in their daily hot flushes versus a 21% reduction obtained with the placebo. "Responders" (defined as patients whose hot flushes were reduced by at least 50% at the end of treatment period) were 65.8% in the soy extract group and 34.2% in the placebo group ( < 0.005). CONCLUSION: Soy isoflavone extract may help to reduce the frequency of hot flushes in climacteric women and provides an attractive addition to the choices available for relief of hot flushes.