Nutrition Articles

The Science Behind Soy

Confused about Soy? You're Not Alone.

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Weight Control
Although weight management is of great interest to many, very few studies have been conducted in this area. The bottom line: Currently, no studies to indicate that soy protein will enhance weight loss.

Infant Formula
If you search the Internet for “infant soy formula” you’ll find countless reported concerns that center on hormone-related changes observed in studies where animals consumed a high amount of isoflavones. There appears to be a lot of hype without scientific basis. Currently the world’s largest soy formula-feeding study is being conducted in the United States, releasing information as it becomes available. So far, it appears that healthy babies on soy formula grow as healthy children should grow and have normal brain functioning and development. The bottom line: While we wait for the final results of this study, parents should discuss breastfeeding and formula feeding with their infant’s health care provider.

Thyroid Function
The results of over 10 clinical trials demonstrate that soy foods and soy isoflavones have little or no effect on thryoid function in healthy adults. However, it has been discovered that individuals taking synthetic thyroid hormone medication may require about a 25% higher dosage of medication if they consume soy foods. Researchers have suggested that the increase in this medication requirement is due to an increase in the medication being excreted in the stool and/or a reduction in medication absorption—not due to a direct effect on the function of the thyroid. If you consume soy products and use thyroid medication, talk to your doctor for appropriate medical care. The bottom line: Soy doesn't appear to damage the thyroid in healthy people or people with thyroid problems. However, people on thyroid medication should talk to their doctors about soy consumption.

The Joy of Eating Soy
Based on the evidence to date, a variety of soy foods, whether fermented or nonfermented, can be included in the daily diet. Health claims stating that nonfermented soy foods contain toxins that block enzyme activity have not been documented by any scientific research. Here are some suggestions for individuals who choose to include soy in their diets.
  • Food is always better than pills. So in this case, eating soy foods is typically safer and more beneficial than soy supplements or pills.
  • For people who want to eat soy products, up to one to two servings per day is appropriate. Examples of a single serving include:
    • 1 cup soymilk
    • 1/2 cup tofu
    • 1/2 cup soy protein (tempeh)
    • 1/2 cup edamame
    • 1/2 cup roasted soy nuts
       
  • For people concerned about GMO (genetically modified organisms) or pesticide exposure, organic soy products are non-GMO and free of pesticides.
  • Be wary of ads and too-good-to-be-true claims for soy-based pills, powders and supplements.
  • For those with a high risk (or history) of estrogen-dependent cancer, soy may be the wrong food. Discuss possible soy consumption with your health care provider, along with medical history, risk factors and treatment options.
While it is not a miracle food, moderate amounts of soy can be part of a healthy diet. As the research on soy continues, it is best, like many things in life, to exercise moderation and caution.
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About The Author

Becky Hand Becky Hand
Becky is a registered and licensed dietitian with almost 20 years of experience. A certified health coach through the Cooper Institute with a master's degree in health education, she makes nutrition principles practical, easy-to-apply and fun. See all of Becky's articles.

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