Phyto-oestrogens and the endometrium

Breast development in the first 2 years of life: an association with soy-based infant formulas

OBJECTIVE

To evaluate the estrogenic effect of soy-based formulas in female infants. These formulas contain significant amounts of phytoestrogens, compounds with structural similarity to estradiol.

PATIENTS AND METHODS

A cross-sectional study consisting of 694 female infants ages 3 to 24 months that consecutively attended 10 general pediatric clinics, none of them having been referred for breast development. The presence of breast buds served as a marker for the endocrine effect of soy-derived phytoestrogens.

RESULTS

Of the participants, 92 had consumed soy formulas for more than 3 months. Breast tissue was more prevalent in the second year of life in infants fed soy-based formula vs those that were breast-fed and those fed dairy-based formula (22.0% vs 10.3%; P = 0.02) with an odds ratio of 2.45 (95% confidence interval 1.11-5.39). No differences in breast bud prevalence were observed during the first year of life. Unlike infants on dairy-based formulas and breast-feeding, infants fed a soy-based formula did not demonstrate a decline in the prevalence of breast during the second year of life.

CONCLUSIONS

We suggest that phytoestrogens impose a preserving effect on breast tissue that is evolved in early infancy, leading eventually to a slower waning of infantile breast tissue.

Effects of dietary equol on body weight gain, intra-abdominal fat accumulation, plasma lipids, and glucose tolerance in ovariectomized Sprague-Dawley rats

OBJECTIVE

To evaluate the effects of dietary equol, a metabolite of the phytoestrogen daidzein, on body weight gain, intra-abdominal fat accumulation, plasma leptin, lipids, and glucose tolerance in ovariectomized rats and to compare them to the effects of 17beta-estradiol.

DESIGN

Twenty-eight female Sprague-Dawley rats were ovariectomized and fed soy-free chow with the addition of estradiol-3 benzoate (E2B) (10 mg/kg, n=10) or equol (400 mg/kg, n=10). The control group (n=8) received soy-free chow only. Weight and food intake were recorded once weekly. After 6 weeks, intra-abdominal fat was measured using computed tomography, and the intraperitoneal glucose tolerance test was performed. In the seventh week, the animals were killed, blood was collected for plasma, and uteri were removed.

RESULTS

Dietary equol significantly increased uterine mass. This effect was, however, 3.5 times lower in magnitude compared to E2B. Similar to E2B, dietary equol decreased weight gain, intra-abdominal fat accumulation, and plasma leptin levels. Equol-treated animals had also lower plasma total cholesterol and triglyceride levels compared to controls. E2B treatment also decreased plasma total cholesterol as well as high-density lipoprotein and low-density lipoprotein cholesterol. In the glucose tolerance test, the area under the curve was significantly smaller in the E2B- and equol-treated animals compared to controls. Also, E2B-treated animals had lower fasting plasma insulin levels.

CONCLUSIONS

In ovariectomized rats, dietary equol administration attenuates weight gain and shows favorable metabolic effects. However, because of its mild uterotrophic activity, its use in the prevention of postmenopausal weight gain and related metabolic disorders in women with an intact uterus is questionable in terms of safety and warrants further studies.

Circulating enterolactone and risk of endometrial cancer

It has been suggested that phytoestrogens protect against hormone-dependent cancers. Lignans are the main class of phytoestrogens in Western diets. We conducted a prospective study of endometrial cancer and circulating levels of the main human lignan, enterolactone. The design was a case-control study nested within 3 prospective cohort studies, in New York, Sweden and Italy. Serum or plasma samples had been collected at enrollment and stored at -80 degrees C. A total of 153 cases, diagnosed a median of 5.3 years after blood donation, and 271 matched controls were included. No difference in circulating enterolactone was observed between cases (median, 19.2 nmol/L) and controls (18.5 nmol/L). Adjusting for body mass index, the odds ratio for the top tertile of enterolactone, as compared to the lowest was 1.2 (95% CI, 0.7-2.0; p for trend = 0.53). Lack of association was observed in both pre- and postmenopausal women. No correlation was observed between enterolactone and circulating estrogens or SHBG in healthy postmenopausal women. These results do not support a protective role of circulating lignans, in the range of levels observed, against endometrial cancer.

Phytoestrogens: end of a tale?

Phytoestrogens are plant-derived hormone-like diphenolic compounds of dietary origin that are present at high levels in plasma of subjects living in areas with low atherosclerosis and cancer incidence. The term phytoestrogen is commonly applied to the soy isoflavones genistein, daidzein and glycitein. As outlined in a previous review article in this journal by Adlercreutz and Mazur 1, these compounds are weakly estrogenic and appear to influence the cardiovascular system, the production, metabolism and biological activity of sex-hormones, as well as malignant cell proliferation, differentiation and angiogenesis. Recently skepticism has developed concerning the true potential of phytoestrogens to beneficially modify these processes. A critical analysis of the early findings from supplementing the diet with soy protein has failed to confirm phytoestrogens as the responsible agent for beneficial cardiovascular effects, be it by way of lipid reduction, vasodilation or lipoprotein oxidation. Furthermore, contrasting data have been reported on the potential of phytoestrogens to prevent hormone-dependent cancers (e.g. breast and prostate) and to successfully treat post-menopausal complaints, an indication for which they are widely used. These potentially negative findings have led health authorities in several countries to suggest maximum daily intake levels for phytoestrogens. There is now growing interest in the use of soy products containing low levels of phytoestrogens and in research on other phytoestrogen free legumes such as lupin.