Stanislaus County Health Services Agency
Soy: The Pros and Cons
Intensive research on soy has shown a number of identifiable benefits as well as a few cautionary flags, especially for using supplements.

About 25 grams of soy protein a day, with its naturally occurring isoflavones, has been found to reduce low density lipoprotein by about 10%.

If you want to add soy to your diet to lower your cholesterol and perhaps to gain other potential health benefits, you’ll need to start slowly.

Soy has been generating a lot of press in recent years. Yet soy is hardly new. Soy products have been around for thousands of years, mainly in Asia where soy is a dietary staple.

Much of soy’s appeal here stems from research showing that Asian peoples have lower rates of heart disease, breast and prostate cancer, fewer hip fractures and fewer hot flashes. It’s easy to oversimplify, however, and many other lifestyle factors such as fat intake and daily exercise levels may also play a role.

Intensive research on soy has shown a number of identifiable benefits to adding soy to our diets as well as a few cautionary flags, especially for using supplements.

Soybeans are highly nutritious. They provide high quality proteins, isoflavones and essential fatty acids. They are low in fat and have no cholesterol.

One of the main components researchers have focused on are isoflavones, particularly genestein and diadzein. These isoflavones in soy are phytoestrogens, weak estrogen-like substances made by plants. They are similar enough to estrogen that they are able to bind to estrogen receptors, possibly explaining how soy might protect against breast cancer, for example.

To date the most compelling evidence in favor of soy is its beneficial effect on cholesterol levels. After decades of study the Food and Drug Administration in October 1999 endorsed soy as a means of lowering cholesterol.

For a soy product to claim it can help lower cholesterol it must meet specific guidelines. Studies showed that it requires about 25 grams of soy protein with its naturally occurring isoflavones per day to reduce low density lipoprotein (LDL) by about 10 percent in individuals with LDL above 160. The closer to normal a person’s LDL level the smaller the beneficial effect.

A soy food claiming it can lower cholesterol must provide at least 6.25 grams of soy protein per single serving. This is about one quarter the daily amount required to show a benefit. The food must also be low in fat (having less than three grams), sodium, saturated fat and cholesterol.

The FDA allows similar claims of cholesterol-lowering effects for the soluble fiber in oat bran and psyllium.

Many Questions Unanswered
Because the chemical structure of isoflavones is similar to that of estrogen, isoflavones bind to estrogen receptors. By competing with estrogen the isoflavones are believed to dampen the effect of estrogen in the body.

This should have a positive effect on the risk of breast cancer which increases with exposure to estrogen. This theory has been supported by animal studies and by observational studies of Asian women who eat diets rich in soy and have lower rates of breast cancer than American women.

A number of recent studies have generated conflicting results. One study of women who were given soy supplements found that fluid from their breasts showed breast cell proliferation, a potential precursor for breast cancer development.

Animal studies also showed human breast cancers transplanted into mice grew at a faster rate when fed with soy isoflavones than controls.

These results and findings of a number of similar studies contradict the assumption that soy protects against breast cancer. Although it may be protective in some cases there may be other instances in which it promotes cancer growth. Further studies are needed and some medical experts caution women against changing their diets to take in very large quantities of soy, particularly in the form of supplements.

There is no evidence to show that soy-based foods eaten in moderation as part of a varied diet, are harmful.

Soy foods have shown promise in lowering the risk of osteoporosis in older women. A study conducted at the University of Illinois showed that soy protein was effective in decreasing the risk of osteoporosis and cardiovascular disease in postmenopausal women.

Apart from the estrogen-like effects of soy isoflavones, researchers believe that soy foods may help build healthy bones by increasing the body’s supply of calcium.

Most of the research on soy related to osteoporosis has been in animal studies and involves very high doses of soy protein. More human studies are needed to determine the usefulness of soy in lowering the risk of osteoporosis.

Although Asian women report fewer problems with hot flashes and other menopausal symptoms than their American counterparts, studies have found very little if any effect on hot flashes when soy was added to the diets of postmenopausal women in the United States.

Adding Soy To Your Diet
If you want to add soy to your diet to lower your cholesterol and perhaps to gain other potential health benefits, you’ll need to start slowly. If you try a soy food and don’t like it, don’t give up. Keep an open mind and try something else.

Tofu can virtually disappear into a dish, taking on the spicy flavors of chili, for example.

Just four ounces of tofu gives you 13 grams of soy protein. Studies showed cholesterol-lowering benefits of soy in those who ate 25 grams of soy protein per day.

Soy milk doesn’t taste like cow’s milk, but if you use 8 ounces in a fruit smoothie, you can get 10 grams of soy protein in a healthy snack. Many people also enjoy the taste of chocolate and vanilla flavored soy milk.

Just one quarter cup of roasted soy nuts gives 19.5 grams of soy protein. Soy nuts have a crunchy, pleasing texture and you can eat them alone or mix them with raisins and other nuts, seeds or dried fruits for a quick and healthy snack.

Muffins made with soy flour and soy protein bars also offer variety and an easy way to add soy without big changes to your diet.

Veggie burgers, soy dogs and soy cheeses can all be incorporated into meals. Try ordering soy-style dishes such as spicy bean curd and miso soup at Asian restaurants. If you like the dish, you can learn how to make it at home.

Any attempt to boost soy consumption long-term should aim for variety. If you rely on only one or two foods to change your diet you’ll get bored.

Most of the uncertainty surrounding soy concerns high doses of isoflavones taken in the form of pills or powders in quantities larger than provided by a normal diet.

By making soy foods part of a healthy, balanced diet you can improve your cholesterol levels and at the same time get the benefits of a low-fat, high quality protein.

John Henkel, “Soy: Health Claims for Soy Protein,” FDA Consumer, May-June 2000.
“FDA Approves Health Claim for Soy Protein,” Physician Assistant, April 2000.
Erik Goldman, “Soy May Help After Menopause, But Won’t Replace HRT,” Family Practice News, November1, 1999.
L. Helmuth, “Nutritionists Debate Soy’s Health Benefits,” Science News, April 1999.
Bonnie Liebman, “The Soy Story,” Nutrition Action Healthletter, September 1998.
Carol Saunders, “Sorting Out Health Claims About Soy,” Patient Care, December 15, 2000.
David Schardt, “Phytoestrogens for Menopause,” Nutrition Action Healthletter, January 2000.
“Soy Substances Slow Prostate Cancer Growth in Animals,” Cancer Weekly, November 15, 1999.
“When It Comes to Soy, Have We Overshot the Mark?” Tufts University Health and Nutrition Letter, May 2000.

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