Maybe becuase scientific literature deviates from supplement company literature:
(1) Hormonal effects of soy in premenopausal women and men.
Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108, USA. firstname.lastname@example.org
Over the past few years, there has been increasing interest in the possible hormonal effects of soy and soy isoflavone consumption in both women and men. Soy consumption has been suggested to exert potentially cancer-preventive effects in premenopausal women, such as increased menstrual cycle length and sex hormone-binding globulin levels and decreased estrogen levels. There has been some concern that consumption of phytoestrogens might exert adverse effects on men's fertility, such as lowered testosterone levels and semen quality.
The studies in women have provided modest support for beneficial effects. One cross-sectional study showed serum estrogens to be inversely associated with soy intake. Seven soy intervention studies controlled for phase of menstrual cycle. These studies provided 32-200 mg/d of isoflavones and generally showed decreased midcycle plasma gonadotropins and trends toward increased menstrual cycle length and decreased blood concentrations of estradiol, progesterone and sex hormone-binding globulin.
A few studies also showed decreased urinary estrogens and increased ratios of urinary 2-(OH) to 16alpha-(OH) and 2-(OH) to 4-(OH) estrogens. Soy and isoflavone consumption does not seem to affect the endometrium in premenopausal women, although there have been weak estrogenic effects reported in the breast. Thus, studies in women have mostly been consistent with beneficial effects, although the magnitude of the effects is quite small and of uncertain significance. Only three intervention studies reported hormonal effects of soy isoflavones in men.
These recent studies in men consuming soyfoods or supplements containing 40--70 mg/d of soy isoflavones showed few effects on plasma hormones or semen quality. These data do not support concerns about effects on reproductive hormones and semen quality.
(2) Effect of soymilk consumption on serum estrogen and androgen concentrations in Japanese men.
Nagata C, Takatsuka N, Shimizu H, Hayashi H, Akamatsu T, Murase K.
Department of Public Health, Gifu University School of Medicine, Japan.
Soy consumption has been associated with a reduced risk of prostate cancer. The mechanism for this association may involve the effect of soy on the endocrine system. We conducted a randomized dietary intervention study to determine the effects of soy consumption on serum levels of steroid hormones in men. Thirty-five men were randomly assigned to either a soymilk-supplemented group or a control group.
The men in the soy-supplemented group were asked to consume 400 ml of soymilk daily for 8 weeks. The men in the control group maintained their usual diet. Blood samples were obtained just before the initiation of the dietary period and thereafter every two weeks for 12 weeks. Changes in hormone concentrations were analyzed and compared between the two groups using the mixed linear regression model against weeks from the start of the dietary period.
The mean (SD) soymilk intake estimated from dietary records during the dietary study period was 342.9 (SD, 74.2) ml in the soymilk-supplemented group. There was a significant difference between the two groups in terms of changes in serum estrone concentrations, which tended to decrease in the soy-supplemented group and increase in the control group over time. None of the other hormones measured (estradiol, total and free-testosterone, or sex hormone-binding globulin) showed any statistical difference between the two groups in terms of patterns of change. The results of the study indicate that soymilk consumption may modify circulating estrone concentrations in men.
Effect of different dietary protein composition on skeletal muscle atrophy by suspension hypokinesia/hypodynamia in rats.
Tada O, Yokogoshi H.
Laboratory of Nutritional Biochemistry, Graduate School of Nutritional and Environmental Sciences, The University of Shizuoka, Japan.
Under microgravity conditions similar to those in space, it is known that various nutritional and physiological changes in the body are induced. Especially in the aspect of nutrition, muscle atrophy is a characteristic phenomenon accompanying weightlessness. This study was conducted to investigate the ameliorated effect of muscle atrophy caused by suspension hypokinesia by using the soy protein isolate (SPI) as the protein source in comparison with casein.
Male Wistar strain rats (8 wk old) were divided into two groups, each suspended with a suspension harness, and fed on a 20% SPI diet or a 20% casein diet for 10 d. The body weights of the suspended rats fed casein or SPI decreased similarly. The weight of the gastrocnemius and soleus muscle were decreased by suspension hypokinesia; however, the degree of the decrease of the muscle weights, especially soleus muscles, of rats fed the SPI diet was smaller than that of rats fed the casein diet. Serum Ntau-methylhistidine concentration was significantly lower in rats fed the SPI diet than in rats fed the casein diet.
Similarly, the activities of muscle protein-degrading enzymes such as calpain and proteasome were significantly lower in rats fed the SPI diet than in rats fed the casein diet. Cathepsin B+L activities were not affected by the SPI or the casein diet. Therefore it is suggested that SPI caused a reduction of the proteolysis of myofibrillar protein in skeletal muscles through a reduction of calpain and proteasome activities, in consequence to ameliorate the muscle atrophy.
Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men.
Haub MD, Wells AM, Tarnopolsky MA, Campbell WW.
Department of Human Nutrition, Kansas State University, Manhattan, KS 66506, USA. email@example.com
BACKGROUND: Aging is associated with reductions in muscle mass and strength, but nutrition and exercise interventions can delay this progression and enhance the quality of life. OBJECTIVE: We examined whether the predominant source of protein consumed by older men influenced measures of muscle size and strength, body composition, resting energy expenditure, and skeletal muscle creatine concentrations in response to 12 wk of resistive training.
DESIGN: After consuming a lactoovovegetarian (LOV) diet for 2 wk, 21 men aged 65 +/- 5 y were randomly assigned to either consume a beef-containing (BC) diet (n = 10) or to continue the LOV diet (n = 11) throughout resistive training. The BC diet included 0.6 g protein. kg(-1). d(-1) from beef and the LOV diet included 0.6 g protein. kg(-1). d(-1) from textured vegetable protein (soy) sources. The remaining protein in the diets came from self-selected LOV sources.
RESULTS: The mean total protein intake for both groups ranged from 1.03 to 1.17 g. kg(-1). d(-1) during the intervention. Men in both groups had improvements (14-38%) in maximal dynamic strength of all the muscle groups trained with no significant difference between groups. With resistive training, cross-sectional muscle area of the vastus lateralis increased in both groups (4.2 +/- 3.0% and 6.0 +/- 2.6% for the LOV and BC groups, respectively) with no significant difference between groups.
Body composition, resting energy expenditure, and concentrations of muscle creatine, phosphocreatine, and total creatine did not differ significantly between groups or change over time. CONCLUSIONS: These data suggest that increases in muscle strength and size were not influenced by the predominant source of protein consumed by older men with adequate total protein intake.