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Beneficial Effects of Soy:

Soy contains valuable constituents, including protein, isoflavones, saponins, and phytosterols. Soy protein provides essential amino acids. Soy is low in fat and cholesterol-free. The isoflavones in soy, primarily genistein and daidzein, have been well researched by scientists for their antioxidant and phytoestrogenic properties. Saponins enhance immune function and bind to cholesterol to limit its absorption in the intestine. Phytosterols and other components of soy have been reported to lower cholesterol levels.

Because soy isoflavones exert mild effects like that of estrogen, they may be useful for treating symptoms associated with menopause. In one double-blind trial, supplementation with 60 grams of soy protein per day for 12 weeks led to a 45% decrease in the number of hot flashes, compared with a 30% reduction in the placebo group, a statistically significant difference. In addition, soy may help regulate hormone levels in premenopausal women.

The phytoestrogens in isoflavones may inhibit cancer-inducing estrogens. Because high estrogen levels are a risk factor for breast cancer, isoflavones may play a role in reducing this risk. Other studies have indicated that isoflavones may actually stimulate the growth of estrogen-dependent breast cancer cells. It has also been reported that high consumption of soy isoflavones may reduce the incidence of prostate cancer in men.

Also of potential benefit to women, isoflavones may support bone health and reduce the effects of osteoporosis. This benefit is being challenged. A well-designed study evaluated the use of ipriflavone, a synthetic isoflavone, in more than 470 postmenopausal women with osteoporosis. Ipriflavone did not prevent bone loss when compared to placebo.

Isoflavones may also support cardiovascular health through a variety of mechanisms. It may help lower cholesterol. Soy milk may help lower blood pressure. After 3 months the individuals consuming soy milk had a modest, but greater, decrease in blood pressure compared to those consuming cow's milk. These benefits could potentially reduce the risk of atherosclerosis and other cardiovascular diseases.

Soybeans and soy foods like tofu are the best dietary source of isoflavones. However, many soy protein concentrates and soy products processed with alcohol may not contain isoflavones. Be sure to check how any soy supplement has been processed. Water washing, while more labor intensive, is best.

Soy Quality Control Checklist

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Side Effects or Interactions

It has been suggested that too much soy can cause thyroid problems, and that soy is
contraindicated for individuals on thyroid medications. Soy intake has not been observed to adversely effect normal thyroid function in human studies.

While it is unlikely that the level of soy consumed by most adults would affect dosage levels of thyroid medications, potential interaction exists. One strategy is to take soy protein and medication at separate times. It is a good idea to also let one's physician know that supplemental soy is being taken so that thyroid levels can be routinely monitored.

Effects of soybeans and foods vs. soy protein isolates

A number of foods, including raw soy beans, members of the cabbage family, and others, contain pro-goitrogens. These substances stimulate the thyroid gland to enlarge, causing what is known as goiter. While unprocessed soy contains these goitrogenic factors, heat applied during the processing of soy protein isolate results in their removal.

Soy infant formula and thyroid dysfunction

While goitrogens can enhance the effects of iodine inadequacy, iodine deficiency is the primary cause of goiter. In the 1960's, there were some reports of goiter inducing-effects observed in soy-formula fed infants. This was related to the inadequate content of iodine in these formulas, not the soy itself. Today, iodine is routinely added to soy formulas.

Apart from the iodine content, the use of soy formula feeding in infancy has been associated in retrospective analyses with autoimmune thyroid disease, and there are ongoing theoretical questions and concerns about soy formula.

There are several reports of medication dosage problems in soy formula fed infants with congenital or hereditary hypothyroidism who were treated with thyroid replacement medication (e.g. synthroid). Soy apparently bound the thyroxine drug in the gastro-intestinal tract and decreased its absorption, requiring an increase in the drug dose.

It does not appear that these effects apply to adults for a number of reasons:

1. Infants respond differently to medications than do adults.
2. The sole diet of these infants was soy, while adults eat a varied diet.
3. There is not a high incidence of thyroid abnormalities in Asian countries where soy intake is common.

Effects of isoflavones and protein components of soy

In vitro (test tube) studies suggest that soy isoflavones may inhibit the action of enzymes involved in thyroid metabolism, namely thyroid peroxidase. It has been speculated that these actions might lead to thyroid problems. To date, however, no consistent changes in thyroid function as measured in several studies have been observed, and no metabolic dysfunction has been reported from human studies.

Soy protein contains a high ratio of arginine to lysine, two naturally occurring amino acid components of all protein. This ratio is thought to stimulate synthesis of the thyroid hormone, thyroxine. In animals (gerbils, hamsters and rats), increase in serum thyroxine levels has been noted when high levels of soy have been fed. In human studies, however, no clear relationship between thyroid hormone concentrations and soy protein ingestion has been noted.

Most importantly, in human studies, serum thyroxine levels have never been observed to rise outside the normal range. Soy researchers have stated that soy does not appear to impact thyroxine levels in humans.

Who Will Benefit From Consuming Soy?

Anyone concerned about:

• angina*
• diabetics* (Nutrition in the News: Protein Shakes Help Outsmart Diabetes )
• family history of breast cancer*
• enlarged prostate*
• cardiovascular disease*
• high cholesterol*
• high triglycerides*
• menopause*
• osteoporosis*
• premenstrual syndrome (PMS)*
• Pregnant women
• Nursing mothers

Biologically Complete Protein From Non-GMO Soy

*

These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.