Effects of replacing meat with soyabean in the diet on sex hormone concentrations in healthy adult males

Abstract

A randomised crossover dietary intervention study was performed to evaluate the effects of replacing meat protein in the diet with a soyabean product, tofu, on blood concentrations of testosterone, dihydrotestosterone, androstanediol glucuronide, oestradiol, sex hormone-binding globulin (SHBG), and the free androgen index (total testosterone concentration/SHBG concentrationÂ100; FAI). Forty-two healthy adult males aged 35±62 years were studied. Diets were isoenergetic, with either 150 g lean meat or 290 g tofu daily providing an equivalent amount of macronutrients, with only the source of protein differing between the two diets. Each diet lasted for 4 weeks, with a 2-week interval between interventions. Fasting blood samples were taken between 07.00 and 09.30 hours. Urinary excretion of genistein and daidzein was significantly higher after the tofu diet P , 0´001X Blood concentrations of sex hormones did not differ after the two diets, but the mean testosterone:oestradiol value was 10 % higher P 0´06 after the meat diet. SHBG was 3 % higher P 0´07Y whereas the FAI was 7 % lower P 0´06Y after the tofu diet compared with the meat diet. There was a significant correlation between the difference in SHBG and testosterone:oestradiol and weight change. Adjusting for weight change revealed SHBG to be 8´8 % higher on the tofu diet (mean difference 3 (95 % CI 0´7, 5´2) nmol/l; P 0´01 and testosterone:oestradiol to be significantly lower, P 0´049X Thus, replacement of meat protein with soyabean protein, as tofu, may have a minor effect on biologically-active sex hormones, which could influence prostate cancer risk. However, other factors or mechanisms may also be responsible for the different incidence rates in men on different diets.

Soy, phytoestrogens and their impact on reproductive health

“…Studies focusing on hormonal levels also found no clear effects (or borderline significance) when consuming tofu (70 mg/day isoflavones), soymilk (48 mg/day isoflavones), or soy products (22 mg/day isoflavones; Habito et al, 2000;Nagata et al, 2000Nagata et al, , 2001. A recent meta-analysis, which included studies that evaluated testosterone levels as a bio-indicator of risks for prostate cancer, suggested out of 32 reports that soy foods or isoflavone intake do not alter free testosterone levels (Hamilton-Reeves et al, 2010).…”

Soybean isoflavone exposure does not have feminizing effects on men: a critical examination of the clinical evidence

“…Nine studies were identified that examined the effects of isoflavone supplements or soy foods on 17b-E 2 and/or estrone levels in men (84)(85)(86)(87)(88)(89)(90)(91)(92). As shown in Table 1, three studies (85,86,92) included older (>40 years) and six (84,(87)(88)(89)(90)(91) included younger men.…”

Clinical and Biological Activity of Soy Protein Powder Supplementation in Healthy Male Volunteers

“…In healthy males, various soy formulations have been evaluated in several studies to determine its effectiveness in decreasing testosterone and ultimately its role in reducing the risk of prostate cancer (15)(16)(17)(18)(19)(20)(21)(22). Most of these studies did not document a significant reduction in circulating testosterone, with the exception of the study by Gardner-Thorpe (18), which used a high concentration of soy isoflavone, and the study by Dillingham (22), which showed a minor reduction of hormone levels.…”