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Soy foods may cause infertility

Posted Jul 24 2009 10:09pm

I know of a lot of people who are using soy in their diets. Some are attempting to start their families and when I read this I thought I would pass it along. I like the fact that this article gives the pros and cons of soy products. I would like to add, however, that I do not eat soy products and am not well versed in their uses so if anyone would like to share their experience with soy products, I would be more then happy to post their comments here!

Sharon LaMothe
Infertility Answers, Inc.

LaMothe Services, LLC

Soy foods may cause infertility

In a previous article on the effects of soy foods, soy supplements and soy-based infant formulas, I reviewed the positive and negative effects of soy as identified by researchers before 2005.

The positive effects included protection against prostate and breast cancer, and reduced cardiovascular disease, as well as non-pharmaceutical treatment of menopausal symptoms such as hot flushes.

On the negative side, there were indications of possible disruption of sexual development in babies who were fed soy-based formulas. There was also the warning that women with a tendency to oestrogen-sensitive breast cancer should avoid high doses of soy products.

More recent studies are now indicating that soy products may also cause infertility, particularly in men.

Endocrine disruptors
Soy foods and supplements contain plant compounds called phytoestrogens and scientists are now investigating if these chemical compounds act as endocrine disruptors – compounds that interfere with normal hormone function.

The latest Arbor Clinical Nutrition Update (2009) poses the question, “Can phytoestrogens cause infertility?” The review published by the Arbor Group lists a number of new studies that have shown various potentially negative effects caused by soy-product supplementation.

For example, a study of 99 men attending a fertility clinic found that those subjects who had the highest soy intake also had the lowest sperm counts compared to men who ate no soy foods.

In another study, researchers compared the effect of two scoops of pure soy protein powder (56g/day) on the testosterone levels of 12 healthy young men. After 4 weeks of using the soy protein powder, the average testosterone levels of the subjects had decreased by 19%. Once the men stopped taking the soy supplement, their testosterone levels returned to normal after about two weeks (Arbor, 2009).

In 1998, Santti and coworkers listed phytoestrogens as potential endocrine disruptors.

An endocrine disruptor binds to oestrogen receptors in the body and hampers production of normal sex hormones. Although there are many different chemicals that can be classified as endocrine disruptors (for example, breakdown products of pesticides and female hormones in our water supply and food chain), results of animal experiments indicate that normal sexual development and behaviour can be negatively influenced by phytoestrogens.

Researchers at the School of Medicine, Queen’s University Belfast, have also identified phytoestrogens as potential endocrine disruptors that may be contributing to the “increased incidence of male reproductive abnormalities and falling sperm counts” (West et al, 2005).

They point out that phytoestrogens, particularly from soy proteins, have become a major component in our typical Western diet. The use of soy-based infant formulas to treat babies that are allergic to cow’s milk is of special concern, because it's believed that the most vulnerable periods when the most serious, and possibly even irreversible damage to the developing sexual organs can occur, are the pre- and neonatal periods (West et al, 2005).

Female problems
Case studies of women who were taking high levels of soy supplements or foods showed that some women develop abnormal bleeding of the uterus, endometriosis and polyps. Removing soy products from their diets improved their symptoms (Chandrareddy et al, 2008).

The medical team reporting these case studies has called for additional research to determine the safety of phytoestrogens in soy supplements used by women, because although these supplements may be beneficial in some cases, they may also cause problems in other cases.

The boom in soy protein use
The past few decades have seen an unprecedented increase in the use of soy foods, soy supplements and soy products in the Western world. If you check practically any food label nowadays, you'll see that manufacturers have added soy protein, or “textured vegetable protein”, as it's also called.

For interest’s sake, I looked at 10 products in my kitchen, ranging from instant oats to biscuits to viennas, and 7 out of 10 products contained “textured vegetable protein”. In addition, you can now buy soy milk, soy ice cream or sorbet, and even ‘soy cheese’.

Then there are the hundreds of sports supplements that all contain vegetable protein or soy flour. In the baby-food category, there are plenty of soy-based formulas to choose from if your baby is allergic to cow’s milk. Finally, women can purchase a wide variety of post-menopausal self-medications to alleviate hot flushes and other unpleasant effects.

In view of the above, it's not incorrect to state that the modern Western diet is being flooded with soy protein and phytoestrogens. The reasons, among others, for this boom in soy protein in our foods and supplements are:

  • The perceived health effects.
  • The fact that textured vegetable protein is less expensive than meat, which is why most sausages, processed meats and hamburger patties contain ever-increasing amounts of vegetable protein.
  • Textured vegetable protein provides good food-processing characteristics (increased water retention, lighter products, etc).
  • It boosts the protein content, lowers the fat and cholesterol contents, and lowers the GI (glycaemic index) of the food.
  • It's used in special foods for people who have allergies to other proteins.
  • Growth of the vegetarian market.

So, while adding soy protein to food products and supplements has beneficial effects, the latest research indicates that we need more investigations to determine if excessive soy intake isn't potentially harmful. For example, it would be ironic if sportsmen who consume vast quantities of soy protein with their muscle-building supplements, are decreasing their testosterone levels. After all, testosterone helps to build lean muscle mass.

As the Arbor team (2009) concludes: from what we know at present, ingesting soy protein can on the one hand be beneficial to prevent hormone-linked cancers of the breast and prostate, but it may well also have negative effects and contribute to infertility.

While we wait for clearer guidelines to emerge from research studies with humans, it may be prudent to only eat moderate quantities of soy-containing foods, not to use soy-containing sports products, only to use soy-based infant formulas under the care of a paediatrician, and only to take soy-based menopausal supplements when prescribed by your gynaecologist.

(, DietDoc, July 2009)

Any questions? Ask DietDoc

(Arbor (2009).Can phytoestrogens cause infertility? Arbor Clinical Nutrition Updates, Issue 308:1-3, June 2009; Chandrareddy A et al. (2008). Adverse effects of phytoestrogens on reproductive health: a report of three cases. Complement Ther Clin Pract. 14(2):132-5; Santti R et al, (1998). Phytoestrogens: potential endocrine disruptors in males. Toxicol Ind Health, 14(1-2):223-37; West MC et al. (2005). Dietary oestrogens and male fertility potential. Hum Fertil, 8(3):197-207.)

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