By: Diana Barnes-Brown for Uterus1
New research examining the effects of soy products on mice has shown that genistein, a major component of soy, can affect the fertility of mice when they are exposed to it in early life.
Genistein is known as a phytoestrogen, or plant estrogen, and can behave similarly to animals’ own estrogen once in the body. Soy products, being derived from the female part of the soy plant, are very rich in genistein. Human foods commonly made with soy products include baby formula and over-the-counter dietary protein supplements.
| Quick facts on soy food products:|
Soy-based food products contain roughly 6 to 9 grams of protein per serving, as compared with similar amounts in eggs and beans, and around 18 to 25 grams per serving of meat or fish.
Soybeans are a common ingredient in East Asian food products, and have been hailed worldwide in recent years as an excellent sustainable protein alternative to animal farming, which requires more land and yields less food than plant-based sources.
Phytoestrogens, or plant estrogens, are present in soybeans and other plant-based foods, and in recent years have been found to have similar positive and negative effects to animal estrogens in the body.
The National Institute of Environmental Health Sciences (NIEHS), a division of the National Institutes of Health, worked with an independent researcher from Syracuse University on the study, which is one of a growing number of similar studies that find soy product consumption could potentially lead to detrimental reproductive outcomes.
Dr. David A. Schwartz, the director of the NIEHS, noted that more research is needed before scientists can determine the exact effects of soy on human reproductive health, but that there is “some reason to be cautious” about human soy intake in the interim.
The study, conducted by Wendy Jefferson, Retha Newbold and Elizabeth Padilla-Banks, of the NIEHS and Melissa Pepling of Syracuse University’s Department of Biology, examined the reproductive effects of giving genistein to newborn baby mice. These figures were then compared with the control group of mice, which did not receive the treatment.
A previous study by the same group had shown that mice that had been exposed to genistein during their newborn days had problems with irregular menstrual cycles, ovulation and fertility as adults. The new study was an attempt to take a closer look at the mechanisms that may cause fertility and reproductive problems in adulthood by examining the effects of genistein on the ovaries during early development.
The mice were split into groups, which were injected with three different doses of genistein on the first through fifth days of life, and the reproductive effects were studied on the second through the sixth day. The doses of genistein were proportional to what would be ingested by a human infant fed on soy formula.
Mice treated with the highest doses of genistein were infertile, while mice treated with lower doses were subfertile, meaning fewer pregnancies and fewer offspring per litter. The mice that received the highest dose of genistein had oocytes (egg cells) that stayed in clusters, rather than separating and developing normally as in mice with healthy reproductive functioning. According to the researchers, oocytes that remain in clusters tend to become fertilized less frequently than unclustered oocytes.
In the study, the most significant finding was observed when ovaries of genistein-treated and non-treated mice were compared at an age of six days; only 36 percent of the oocytes in treated mice were unclustered, as compared to 57 percent of the oocytes of their untreated counterparts.
“We have shown that genistein alters ovarian differentiation during neonatal development,” wrote the researchers. “Ovaries from neonatal mice treated with genistein have more oocytes not enclosed in follicles, more oocytes persisting in nests, and retention of oocyte intercellular bridges.” In closing, the researchers noted that “disruption of these pathways can lead to alterations in the normal progression of ovarian development and subsequent normal ovarian function.”
While these findings have yet to be replicated in humans, they do add to growing concern that soy products – once considered a “miracle food” by those who placed dietary emphasis on health, animal rights and environmental sustainability – may carry with them significant consequences that must be understood.