The estrogen debate

Dr. Daniel erroneously stated that Asians consume 9 to 36 grams of total soy foods--or 1/3 to 1 1/2 ounces of these foods--per day, based on her analysis of two sources. The first report she used is one with which I'm very familiar, since I commissioned this document while serving as a program director in the government's National Cancer Institute.

The author failed to understand this report, as well as another source she used to suggest that Japanese consume only 18 grams of soy food per day. In both cases, Dr. Daniel confused foods measured in their natural whole food weight (called wet weight) with those in the dehydrated (dry weight) state.

Dr. Daniel could have easily cited better estimates of soy food consumption in Asia by referring to the Food and Agriculture Organization's (FAO) website: http://apps.fao.org/default.jsp. According to this source, the average Japanese citizen consumes 8.6 grams of soy protein per day. This translates to about one serving of soy, since the average serving size provides about 7 to 10 grams of soy protein. Since the FAO averages soy intake among the entire population, including infants, children, and adults, it can be expected that soy intake among adults is actually even higher than this.

Eleven well-designed clinical studies failed to find any harmful effect of soy protein or isoflavones on thyroid function in healthy adults.

While soy foods are one of many protein-rich foods that can cause allergic reactions in some individuals (others are milk, eggs, and peanuts), the incidence of soy allergy is much lower than the incidence of allergies to many protein-rich foods Americans enjoy, and the allergic response to soy is generally much less severe. Obviously, those with allergic reactions to soy protein should avoid these foods, but this is something that affects only an extremely small percentage of the population.

It is true that soy isoflavones can bind to the same receptors in cells that bind the hormone estrogen. Soy isoflavones are not the same as estrogen. Experts on these compounds recognize that it is not possible to draw conclusions about the biological activities of soy based on the effects of the hormone estrogen.

Birth defects in male offspring have not been linked specifically to maternal consumption of soy foods or isoflavones.

Finally, numerous studies have compared the effects of soy consumption within Asia. This research shows that those Asians who consume more soy foods have lower rates of heart disease, prostate cancer, and osteoporosis than Asians with lower-than-average consumption of soy foods. Soy foods can be an excellent means of broadening a child's options for nutritious foods.

MARK MESSINA, PHD

Adjunct Associate Professor

Department of Nutrition

Loma Linda University

President, Nutrition Matters, Inc.

Port Townsend, Washington

Dr. Daniel responds: Although Dr. Messina's figures on soy consumption are far higher than those provided by other sources that he considers less reputable, they still provide a valuable corrective to the widely held misconception that Asians eat a great deal of soy. Dr. Messina's figure of soy protein at 8.6 grams per day is dramatically lower than the FDA's health claim recommending 25 grams per day. The amount he cites is also lower than the quantities of soy consumed by many vegetarians and others today.

Soy allergies are on the rise, and soy is now widely considered to be one of the top eight allergens. Some experts put it in the top four, This is a very serious and life-threatening problem in that soy is included in just about every processed food today.

Dr. Messina is correct that the subject of estrogens is highly complex. The important thing to remember is that plant estrogens are not "weak," can exert adverse effects, and have not been proven sale.

Birth defects have been linked to soy foods or soy isoflavones in every animal species studied. The human study linking hypospadias to maternal vegetarian diets concerned phytoestrogens. Soy is the only commonly eaten food that contains high quantities of phytoestrogens.

Until safety has been conclusively proven, I do not share Dr. Messina's belief that soy foods should constitute more than a minimal part of a child's diet.

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