One of the classic criticisms levied by industry at concerns about synthetic endocrine disrupting chemicals (EDCs) has been to point to all the plant compounds that are in the human diet that are also capable of acting as hormones. These plant compounds, called phytoestrogens, are especially abundant in foods like soy.

Early on in the debate about Our Stolen Future, industry spokespeople would trot out complex tables with calculations performed out to 4 decimal places showing that phytoestrogens were literally thousands of times more abundant in our food than are synthetic compounds. The tables looked very quantitative and precise, and proved to be formidable tools in public presentations for audiences not familiar with the science. What these tables really showed, however, was that it is possible to be very precise but completely wrong.

This argument appears less frequently now because it has been shown to be misguided. What comes in through the mouth doesn't necessarily make it to the fetus to influence fetal development.

• Most of the plant compounds are de-activated even before being absorbed by the gut, if they are absorbed at all. So they don't even make it into the bloodstream, much less to the fetus.
• Those that are absorbed into the blood are often deactivated or diminished in quantity by natural chemicals in the blood, called serum binding proteins, then act on the compounds that enter the blood. Serum binding proteins are highly effective at binding some compounds and not at others. On average, the binding proteins are more effective against plant phytoestrogens than synthetic EDCs. Fortunately, some EDCs are also "captured" by serum-binding proteins.
• EDCs typically have far longer half-lives in the human body than do phytoestrogens. Once ingested, the half-life of DDT can be a decade. Phytoestrogens are far less persistent. They don't hang around.
• Many, but not all, synthetic EDCs bioaccumulate. Their chemical characteristics result in their being stored in body fat. Over years of exposure, they reach concentrations that can be thousands of times higher than the levels found in the diet. Phytoestrogens, in contrast, do not bioaccumulate.

In essence, these differences between synthetic EDCs and phytoestrogens are not about synthetic vs natural per se, but about specific aspects of the chemistry of the molecules involved and the chemistry of the human body. People possess chemical defenses which protect against at least some of the phytoestrogens (see OSF Chapter 5).

In part because they avoid these defenses, persistent synthetic endocrine disruptors accumulate in body tissue to levels that are orders of magnitude of times higher than observed levels for phytoestrogens, and some are then transferred to the developing fetus. Framing the debate solely around the relative amounts of phytoestrogens vs. synthetic chemicals that are encountered in the diet also ignores the large exposures that can occur at the workplace or elsewhere independent of food.

Continuing research into this issue will no doubt reveal a far more complex picture concerning natural defenses vs. synthetic and natural hazards. Indeed, a key part of the ongoing research will explore why the body's defense mechanisms are effective against some but not all compounds. While far from the final word, these new results do, however, counter the claim that the presence of plant estrogens in the human diet is sufficient reason to dismiss concern about synthetic compounds. It is clearly not.

In the meantime, if you hear a speaker claiming that phytoestrogens make synthetic EDCs irrelevant, understand that this person is either way out-of-date as to how research on this has developed, shameless in their willingness to use disproven arguments, or both.

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