Effects of wheat bran on blood and tissue hormone levels in adult female rats

Abstract

Arts CJM, Thijssen JHH. Effects of wheat bran on blood and tissue hormone levels in adult female rats.The protective effect of dietary fiber on breast cancer development might be explained by the interaction between dietary fiber and hormonal processes. We studied the effects of dietary fiber and the effects of a reduced energy intake on the exposure of mammary tissue to both estrogens and progesterone, as well as the blood plasma levels of these steroids and of LH and FSH. Adult female Fisher rats were fed ad libitum either a low-fiber diet (0.5% dietary fiber based on wheat flour) or a high-fiber diet (9.2% dietary fiber based on wheat bran). A third group was used to control for the reduced energy intake of the hi gh\ x=req-\ fiber group and was fed the low-fiber diet restricted. Energy intake was similar for the second and third groups. Four out of 14 rats of the high-fiber group and 4 out of 15 rats of the restricted low-fiber groups were not in cycle after seven weeks on the experimental diets, indicating that the estrous cycle was significantly affected by a reduced energy intake. Exposure of mammary tissue to estrogens did not differ among the groups, as measured by estrone, estradiol-17\g=b\,estriol and peroxidase activity. During the peak period, plasma LH levels were significantly higher in the high-fiber group than in the two low-fiber groups. FSH and progesterone plasma levels were unaffected by the experimental diets. It is concluded that dietary fiber affects the hormonal processes involved in breast cancer development. The increased LH levels indicate an increased estrogen production in the ad libitum high-fiber group. Cor JM Arts, TNO/Toxicology and Nutrition Institute, In various studies an inverse relation has been observed between dietary fiber intake and breast or mammary cancer. Lower plasma estrogen levels have been meas¬ ured in vegetarian postmenopausal women (1), and a reduced risk of breast cancer has been observed in women with a relatively high intake of dietary fiber (2). In two lifespan studies (3, 4), mammary cancer inci¬ dence was significantly lower in rats fed a high-fiber (HF) diet than in those on a low-fiber (LF) diet. Moreover, NMU-induced mammary tumors in rats fed a HF diet weighed significantly less than those in rats fed a LF diet (5,6). Estrogens have been reported to play a crucial role in mammary carcinogenesis. An increased exposure of the estrogen-sensitive tissue to estrogens would result in a higher risk of mammary cancer at the initiation or promotion phase (7). In a previous study (5), a clear interruption of the enterohepatic circulation of estrogens was observed, resulting in a three to fourfold higher fecal estrogen excretion in rats fed the HF diet than in those fed the LF diet, contrary to urinary estrone (Ei ) excretion, which was lower (p<0.05) in the HF group. Despite the increased fecal estrogen excretion, plasma estradiol-17ß (E2) levels were similar in both groups. This latter finding may be explained by a negative feedback mechanism, i.e. an increase...

Dietary fiber is associated with serum sex hormones and insulin-related peptides in postmenopausal breast cancer survivors

“…Dietary fiber increases the fecal excretion of estrogen [11] and binds estradiol [12] thereby reducing bio-available levels; and most studies in humans have found that estrogen levels decrease as dietary fiber increases [17,19,[34][35][36][37]. Dietary fiber may also influence estrogen levels through its regulation of body weight.…”