Green tea extract and catechol-O-methyltransferase genotype modify the post-prandial serum insulin response in a randomised trial of overweight and obese post-menopausal women.

BACKGROUND: Green tea extract (GTE) may be involved in a favourable post-prandial response to high-carbohydrate meals. The catechol-O-methyltransferase (COMT) genotype may modify these effects. We examined the acute effects of GTE supplementation on the post-prandial response to a high-carbohydrate meal by assessing appetite-associated hormones and glucose homeostasis marker concentrations in women who consumed 843 mg of (-)-epigallocatechin-3-gallate (EGCG) or placebo capsules for 11-12 months. METHODS: Sixty Caucasian post-menopausal women (body mass index ≥ 25.0 kg m-2 ) were included in a randomised, double-blind feeding study. GTE was consumed with a breakfast meal [2784.0 kJ (665.4 kcal); 67.2% carbohydrate]. Blood samples were drawn pre-meal, post-meal, and every 30 min for 4 h. Participants completed six satiety questionnaires. RESULTS: Plasma leptin, ghrelin and adiponectin did not differ between GTE and placebo at any time point; COMT genotype did not modify these results. Participants randomised to GTE with the high-activity form of COMT (GTE-high COMT) had higher insulin concentrations at time 0, 0.5 and 1.0 h post-meal compared to all COMT groups randomised to placebo. Insulin remained higher in the GTE-high COMT group at 1.5, 2.0 and 2.5 h compared to Placebo-low COMT (P < 0.02). GTE-high COMT had higher insulin concentrations at times 0, 0.5, 1.0, 1.5 and 2.0 h compared to the GTE-low COMT (P ≤ 0.04). Area under the curve measurements of satiety did not differ between GTE and placebo. CONCLUSIONS: GTE supplementation and COMT genotype did not alter acute post-prandial responses of leptin, ghrelin, adiponectin or satiety, although it may be involved in post-meal insulinaemic response of overweight and obese post-menopausal women.

Consumption of Lactobacillus acidophilus and Bifidobacterium longum do not alter urinary equol excretion and plasma reproductive hormones in premenopausal women.

OBJECTIVE: To confirm the results of an earlier study showing premenopausal equol excretors to have hormone profiles associated with reduced breast cancer risk, and to investigate whether equol excretion status and plasma hormone concentrations can be influenced by consumption of probiotics. DESIGN: A randomized, single-blinded, placebo-controlled, parallel-arm trial. SUBJECTS: In all, 34 of the initially enrolled 37 subjects completed all requirements. INTERVENTION: All subjects were followed for two full menstrual cycles and the first seven days of a third cycle. During menstrual cycle 1, plasma concentrations of estradiol (E(2)), estrone (E(1)), estrone-sulfate (E(1)-S), testosterone (T), androstenedione (A), dehydroepiandrosterone-sulfate (DHEA-S), and sex-hormone-binding globulin (SHBG) were measured on cycle day 2, 3, or 4, and urinary equol measured on day 7 after a 4-day soy challenge. Subjects then received either probiotic capsules (containing Lactobacillus acidophilus and Bifidobacterium longum) or placebo capsules through day 7 of menstrual cycle 3, at which time both the plasma hormone concentrations and the post-soy challenge urinary equol measurements were repeated. RESULTS: During menstrual cycle 1, equol excretors and non-excretors were not significantly different with respect to subject characteristics, diet, or hormone concentrations. Significant inverse correlations were found between E(2) and body mass index (BMI) (P=0.02), SHBG and BMI (P=0.01), DHEA-S and dietary fiber (P=0.04), and A and protein:carbohydrate ratio (P=0.02). Probiotic consumption failed to significantly alter equol excretor status or hormone concentrations during menstrual cycle 3, although there were trends towards decreased concentrations of T (P=0.14) and SHBG (P=0.10) in the probiotic group. CONCLUSIONS: We were unable to verify a previously reported finding of premenopausal equol excretors having plasma hormone concentrations different from those of nonexcretors. Furthermore, a 2-month intervention with probiotic capsules did not significantly alter equol excretion or plasma hormone concentrations.

Lack of effect of isoflavonic phytoestrogen intake on leptin concentrations in premenopausal and postmenopausal women.

OBJECTIVE: To assess the effect of soy isoflavone ingestion on plasma leptin concentrations in premenopausal and postmenopausal women. DESIGN: Randomized, crossover studies, with blinding of participants and laboratory personnel. SETTING: Procedures involving free-living individuals were carried out at the University of Minnesota General Clinical Research Center. PATIENT(S): Fourteen regularly cycling premenopausal women, and 18 postmenopausal women. INTERVENTION(S): Each premenopausal participant consumed, on a daily basis, each of three soy protein powders containing different levels of isoflavones for three menstrual cycles plus 9 days, with plasma samples collected every other day the last 6 weeks of each diet period. Similarly, each postmenopausal participant consumed each of the three powders for 93 days, with plasma samples collected daily on days 64 to 66 and 92 to 94 of each diet period. The powders, dosed on a per-kilogram body weight basis, provided mean isoflavone intakes of 8, 65, and 130 mg/day, for the control, low-isoflavone, and high-isoflavone diet periods, respectively. MAIN OUTCOME MEASURE(S): Plasma leptin concentrations. RESULT(S): Isoflavone intake had essentially no effect on leptin concentrations in either premenopausal or postmenopausal participants. Concentrations in the premenopausal women were higher during the periovulatory and midluteal phases as compared to the early follicular and midfollicular phases. CONCLUSION(S): Despite the well-documented effect of estrogens to enhance leptin production, even high levels of isoflavone consumption do not alter leptin concentrations in women. Further studies are needed to more precisely delineate the nature of estrogenic and/or antiestrogenic effects of isoflavones in humans.

Soy consumption alters endogenous estrogen metabolism in postmenopausal women.

Isoflavones are soy phytoestrogens that have been suggested to be anticarcinogenic. Our previous study in premenopausal women suggested that the mechanisms by which isoflavones exert cancer-preventive effects may involve modulation of estrogen metabolism away from production of potentially carcinogenic metabolites [16alpha-(OH) estrone, 4-(OH) estrone, and 4-(OH) estradiol] (X. Xu et al., Cancer Epidemiol. Biomark. Prev., 7: 1101-1108, 1998). To further evaluate this hypothesis, a randomized, cross-over soy isoflavone feeding study was performed in 18 healthy postmenopausal women. The study consisted of three diet periods, each separated by a washout of approximately 3 weeks. Each diet period lasted for 93 days, during which subjects consumed their habitual diets supplemented with soy protein isolate providing 0.1 (control), 1, or 2 mg isoflavones/kg body weight/day (7.1 +/- 1.1, 65 +/- 11, or 132 +/- 22 mg/day). A 72-h urine sample was collected 3 days before the study (baseline) and days 91-93 of each diet period. Urine samples were analyzed for 10 phytoestrogens and 15 endogenous estrogens and their metabolites by a capillary gas chromatography-mass spectrometry method. Compared with the soy-free baseline and very low isoflavone control diet, consumption of 65 mg isoflavones increased the urinary 2/16alpha-(OH) estrone ratio, and consumption of 65 or 132 mg isoflavones decreased excretion of 4-(OH) estrone. When compared with baseline values, consumption of all three soy diets increased the ratio of 2/4-(OH) estrogens and decreased the ratio of genotoxic: total estrogens. These data suggest that both isoflavones and other soy constituents may exert cancer-preventive effects in postmenopausal women by altering estrogen metabolism away from genotoxic metabolites toward inactive metabolites.

Effects of soy isoflavones on estrogen and phytoestrogen metabolism in premenopausal women.

Isoflavones and lignans are soy phytoestrogens that have been suggested to be anticarcinogenic. The mechanisms by which they exert cancer-preventive effects may involve modulation of estrogen synthesis and metabolism. To evaluate this hypothesis, a randomized, cross-over soy isoflavone feeding study was performed in 12 healthy premenopausal women. The study consisted of three diet periods, each separated by a washout of approximately 3 weeks. Each diet period lasted for three menstrual cycles plus 9 days (averaging approximately 100 days), during which subjects consumed their habitual diets supplemented with soy protein powder providing 0.16 (control diet), 1.01, or 2.01 mg of total isoflavones per kg of body weight per day (10+/-1.1, 65+/-9.4, or 129+/-16 mg/day, respectively). A 72-h urine sample was collected during the midfollicular phase (days 7-9) of the fourth menstrual cycle in each diet period. Urine samples were analyzed for 10 phytoestrogens and 15 endogenous estrogens and their metabolites by a capillary gas chromatography-mass spectrometry method. Urinary excretion of isoflavonoids and lignans significantly increased with increased isoflavone consumption. Compared with the control diet, increased isoflavone consumption decreased urinary excretion of estradiol, estrone, estriol, and total estrogens, as well as excretion of the hypothesized genotoxic estrogen metabolites, 16alpha-hydroxyestrone, 4-hydroxyestrone, and 4-hydroxyestradiol. Of importance are the observations of a significant increase in the 2-hydroxyestrone/16alpha-hydroxyestrone ratio and a decrease in the genotoxic/total estrogens ratio. These data suggest that soy isoflavone consumption may exert cancer-preventive effects by decreasing estrogen synthesis and altering metabolism away from genotoxic metabolites toward inactive metabolites.

Effects of phytoestrogens on DNA synthesis in MCF-7 cells in the presence of estradiol or growth factors.

Phytoestrogen effects on estrogen action and tyrosine kinase activity have been proposed to contribute to cancer prevention. To study these mechanisms, a number of phytoestrogens and related compounds were evaluated for their effects on DNA synthesis (estimated by thymidine incorporation analysis) in estrogen-dependent MCF-7 cells in the presence of estradiol (E2), tamoxifen, insulin, or epidermal growth factor. We observed that 1) at 0.01-10 microM, genistein and coumestrol enhanced E2-induced DNA synthesis, as did 10 microM enterolactone. Chrysin at 1.0-10 microM and 10 microM luteolin or apigenin inhibited E2-induced DNA synthesis, as did all compounds at > 10 microM, 2) tamoxifen enhanced genistein-induced DNA synthesis but inhibited DNA synthesis induced by all other compounds, and 3) genistein enhanced insulin- and epidermal growth factor-induced DNA synthesis at 0.1-1.0 and 0.1-10 microM, respectively. At higher concentrations, inhibition was observed. Similar effects were seen with coumestrol. In conclusion, the effects of phytoestrogens in the presence of E2 or growth factors are concentration dependent and variable. At low concentrations, genistein and coumestrol significantly enhanced E2-induced and tyrosine kinase-mediated DNA synthesis; at high concentrations, inhibition was observed. Differing effects were observed with the other compounds. The variable effects of phytoestrogens on DNA synthesis must be considered when their roles in cancer prevention or treatment are evaluated.

Dietary phytoestrogens.

Broadly defined, phytoestrogens include isoflavones, coumestans, and lignans. A number of these compounds have been identified in fruits, vegetables, and whole grains commonly consumed by humans. Soybeans, clover and alfalfa sprouts, and oilseeds (such as flaxseed) are the most significant dietary sources of isoflavones, coumestans, and lignans, respectively. Studies in humans, animals, and cell culture systems suggest that dietary phytoestrogens play an important role in prevention of menopausal symptoms, osteoporosis, cancer, and heart disease. Proposed mechanisms include estrogenic and antiestrogenic effects, induction of cancer cell differentiation, inhibition of tyrosine kinase and DNA topoisomerase activities, suppression of angiogenesis, and antioxidant effects. Although there currently are no dietary recommendations for individual phytoestrogens, there may be great benefit in increased consumption of plant foods.

Phytoestrogen concentration determines effects on DNA synthesis in human breast cancer cells.

Thirteen isoflavonoids, flavonoids, and lignans, including some known phytoestrogens, were evaluated for their effects on DNA synthesis in estrogen-dependent (MCF-7) and -independent (MDA-MB-231) human breast cancer cells. Treatment for 24 hours with most of the compounds at 20-80 microM sharply inhibited DNA synthesis in MDA-MB-231 cells. In MCF-7 cells, on the other hand, biphasic effects were seen. At 0.1-10 microM, coumestrol, genistein, biochanin A, apigenin, luteolin, kaempferol, and enterolactone induced DNA synthesis 150-235% and, at 20-90 microM, inhibited DNA synthesis by 50%. Treatment of MCF-7 cells for 10 days with genistein or coumestrol showed continuous stimulation of DNA synthesis at low concentrations. Time-course experiments with genistein in MCF-7 cells showed effects to be reversed by 48-hour withdrawal of genistein at most concentrations. Induction of DNA synthesis in MCF-7 cells, but not in MDA-MB-231 cells, is consistent with an estrogenic effect of these compounds. Inhibition of estrogen-dependent and -independent breast cancer cells at high concentrations suggests additional mechanisms independent of the estrogen receptor. The current focus on the role of phytoestrogens in cancer prevention must take into account the biphasic effects observed in this study, showing inhibition of DNA synthesis at high concentrations but induction at concentrations close to probable levels in humans.

Effect of the menstrual cycle on energy and nutrient intake.

Midfollicular and midluteal dietary intakes of 18 women were evaluated between four and six ovulatory menstrual cycles. Phase lengths were established by basal body temperatures and urinary luteinizing hormone excretion. Midfollicular and midluteal diet records were collected 6-8 d after menstrual onset and 6-8 d after ovulation, respectively. Significant increases in energy [0.66 MJ (159 kcal), P = 0.003], protein (6.1 g, P = 0.02), carbohydrate (15.3 g, P = 0.04), and fat (8.6 g, P = 0.002) intakes were observed in midluteal phase when compared with midfollicular phase. Intakes of vitamin D, riboflavin, potassium, phosphorus, and magnesium also were significantly higher during midluteal phase (P < 0.05). These results support the regulation of food intake by menstrual cycle hormones and suggest that it is essential to consider phase of menstrual cycle in studies of nutrient intake performed in premenopausal women.

Effect of flax seed ingestion on the menstrual cycle.

Lignans are a group of phytochemicals shown to have weakly estrogenic and antiestrogenic properties. Two specific lignans, enterodiol and enterolactone, are absorbed after formation in the intestinal tract from plant precursors particularly abundant in fiber-rich food and are excreted in the urine. We evaluated the effect of the ingestion of flax seed powder, known to produce high concentrations of urinary lignans, on the menstrual cycle in 18 normally cycling women, using a balanced randomized cross-over design. Each subject consumed her usual omnivorous, low fiber (control) diet for 3 cycles and her usual diet supplemented with flax seed for another 3 cycles. The second and third flax cycles were compared to the second and third control cycles. Three anovulatory cycles occurred during the 36 control cycles, compared to none during the 36 flax seed cycles. Compared to the ovulatory control cycles, the ovulatory flax cycles were consistently associated with longer luteal phase (LP) lengths (mean +/- SEM, 12.6 +/- 0.4 vs. 11.4 +/- 0.4 days; P = 0.002). There were no significant differences between flax and control cycles for concentrations of either estradiol or estrone during the early follicular phase, midfollicular phase, or LP. Although flax seed ingestion had no significant effect on LP progesterone concentrations, the LP progesterone/estradiol ratios were significantly higher during the flax cycles. Midfollicular phase testosterone concentrations were slightly higher during flax cycles. Flax seed ingestion had no effect on early follicular phase concentrations of DHEA-S, PRL, or sex hormone-binding globulin. Our data suggest a significant specific role for lignans in the relationship between diet and sex steroid action, and possibly between diet and the risk of breast and other hormonally dependent cancers.